16" DC Fan Low Power Consumption 3.5 Watts / Hour - 8 - low power consumption

TFT LCDvs OLED

Seino Y, Sasabe H, Pu YJ, Kido J . High-performance blue phosphorescent OLEDs using energy transfer from exciplex. Adv Mater 2014; 26: 1612–1616.

Kim KH, Lee K, Park SB, Song JK, Kim SN et al. Domain Divided Vertical Alignment Mode with Optimized Fringe Field Effect. Proceedings of the 18th IDRC, Asia Display 1998; 98: 383–386.

Several different families of liquid crystals are used in liquid crystal displays. The molecules used have to be anisotropic, and to exhibit mutual attraction. Polarizable rod-shaped molecules (biphenyls, terphenyls, etc.) are common. A common form is a pair of aromatic benzene rings, with a nonpolar moiety (pentyl, heptyl, octyl, or alkyl oxy group) on one end and polar (nitrile, halogen) on the other. Sometimes the benzene rings are separated with an acetylene group, ethylene, CH=N, CH=NO, N=N, N=NO, or ester group. In practice, eutectic mixtures of several chemicals are used, to achieve wider temperature operating range (−10..+60 °C for low-end and −20..+100 °C for high-performance displays). For example, the E7 mixture is composed of three biphenyls and one terphenyl: 39 wt.% of 4'-pentyl[1,1'-biphenyl]-4-carbonitrile (nematic range 24..35 °C), 36 wt.% of 4'-heptyl[1,1'-biphenyl]-4-carbonitrile (nematic range 30..43 °C), 16 wt.% of 4'-octoxy[1,1'-biphenyl]-4-carbonitrile (nematic range 54..80 °C), and 9 wt.% of 4-pentyl[1,1':4',1-terphenyl]-4-carbonitrile (nematic range 131..240 °C).[173]

We have briefly reviewed the recent progress of LCD and OLED technologies. Each technology has its own pros and cons. For example, LCDs are leading in lifetime, cost, resolution density and peak brightness; are comparable to OLEDs in ACR, viewing angle, power consumption and color gamut (with QD-based backlights); and are inferior to OLED in black state, panel flexibility and response time. Two concepts are elucidated in detail: the motion picture response time and ACR. It has been demonstrated that LCDs can achieve comparable image motion blur to OLEDs, although their response time is 1000 × slower than that of OLEDs (ms vs. μs). In terms of the ACR, our study shows that LCDs have a comparable or even better ACR than OLEDs if the ambient illuminance is >50 lux, even if its static CR is only 5000:1. The main reason is the higher brightness of LCDs. New trends for LCDs and OLEDs are also highlighted, including ultra-high peak brightness for HDR, ultra-high-resolution density for VR, ultra-low power consumption for AR and ultra-versatile functionality for vehicle display, transparent display and mirror display applications. The competition between LCDs and OLEDs is still ongoing. We believe these two TFT-based display technologies will coexist for a long time.

Jou JH, Kumar S, Agrawal A, Li TH, Sahoo S . Approaches for fabricating high efficiency organic light emitting diodes. J Mater Chem C 2015; 3: 2974–3002.

In 1972, the concept of the active-matrix thin-film transistor (TFT) liquid-crystal display panel was prototyped in the United States by T. Peter Brody's team at Westinghouse, in Pittsburgh, Pennsylvania.[46] In 1973, Brody, J. A. Asars and G. D. Dixon at Westinghouse Research Laboratories demonstrated the first thin-film-transistor liquid-crystal display (TFT LCD).[47][48] As of 2013[update], all modern high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays.[49] Brody and Fang-Chen Luo demonstrated the first flat active-matrix liquid-crystal display (AM LCD) in 1974, and then Brody coined the term "active matrix" in 1975.[42]

Kondakov DY, Sandifer JR, Tang CW, Young RH . Nonradiative recombination centers and electrical aging of organic light-emitting diodes: direct connection between accumulation of trapped charge and luminance loss. J Appl Phys 2003; 93: 1108–1109.

The origin and the complex history of liquid-crystal displays from the perspective of an insider during the early days were described by Joseph A. Castellano in Liquid Gold: The Story of Liquid Crystal Displays and the Creation of an Industry.[7] Another report on the origins and history of LCD from a different perspective until 1991 has been published by Hiroshi Kawamoto, available at the IEEE History Center.[27] A description of Swiss contributions to LCD developments, written by Peter J. Wild, can be found at the Engineering and Technology History Wiki.[28]

Baldo MA, Lamansky S, Burrows PE, Thompson ME, Forrest SR . Very high-efficiency green organic light-emitting devices based on electrophosphorescence. Appl Phys Lett 1999; 75: 4–6.

Jo JH, Jhe JH, Ryu SC, Lee KH, Shin JK . A novel curved LCD with highly durable and slim profile. SID Symp Dig Tech Pap 2010; 41: 1671–1674.

Schadt M, Seiberle H, Schuster A . Optical patterning of multi-domain liquid-crystal displays with wide viewing angles. Nature 1996; 381: 212–215.

Generally, each layer in an OLED is quite thin, and the total thickness of the whole device is <1 μm (substrates are not included). Thus the OLED is a perfect candidate for flexible displays. For an intrinsic organic material, its carrier mobility (<0.1 cm2 Vs−1) and free carrier concentration (1010 cm−3) are fairly low, limiting the device efficiency. Thus doping technology is commonly used42, 43. Additionally, to generate white light, two configurations can be considered: (1) patterned red, green and blue (RGB) OLEDs; and (2) a white OLED with RGB color filters (CFs). Both have pros and cons. In general, RGB OLEDs are mostly used for small-sized mobile displays, while white OLEDs with CFs are used for large TVs.

Oh-e M, Kondo K . Response mechanism of nematic liquid crystals using the in-plane switching mode. Appl Phys Lett 1996; 69: 623–625.

IPS mode was first proposed in 1973 by Soref15 but remained a scientific curiosity until the mid-1990s owing to the demand of touch panels33, 34. In an IPS cell, the LC directors are homogeneously aligned and the electric fields are in the lateral direction (Figure 2c). As the voltage increases, the strong in-plane fringing electric fields between the interdigital electrodes reorient the LC directors. Such a unique mechanism makes IPS a favorable candidate for touch panels because no ripple effect occurs upon touching the panel. However, the peak transmittance of IPS is relatively low (~75%) because the LC molecules above the electrodes cannot be effectively reoriented. This low transmittance region is called a dead zone5.

Käläntär K . A directional backlight with narrow angular luminance distribution for widening the viewing angle for an LCD with a front-surface light-scattering film. J Soc Inf Display 2012; 20: 133–142.

Scholz S, Kondakov D, Lüssem B, Leo K . Degradation mechanisms and reactions in organic light-emitting devices. Chem Rev 2015; 115: 8449–8503.

Illustration of the emission mechanisms of OLEDs: (a) fluorescence, (b) TTF, (c) phosphorescence, and (d) TADF. ISC, intersystem crossing; RISC, reverse intersystem crossing; TF, triplet fusion.

STN LCDs have to be continuously refreshed by alternating pulsed voltages of one polarity during one frame and pulses of opposite polarity during the next frame. Individual pixels are addressed by the corresponding row and column circuits. This type of display is called passive-matrix addressed, because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Slow response times and poor contrast are typical of passive-matrix addressed LCDs with too many pixels and driven according to the "Alt & Pleshko" drive scheme. Welzen and de Vaan also invented a non RMS drive scheme enabling to drive STN displays with video rates and enabling to show smooth moving video images on an STN display.[citation needed] Citizen, among others, licensed these patents and successfully introduced several STN based LCD pocket televisions on the market.[citation needed]

Lin HY, Chen KY, Ho YH, Fang JH, Hsu SC et al. Luminance and image quality analysis of an organic electroluminescent panel with a patterned microlens array attachment. J Optics 2010; 12: 085502.

DBEF polarizers using uniaxial oriented polymerized liquid crystals (birefringent polymers or birefringent glue) were invented in 1989 by Philips researchers Dirk Broer, Adrianus de Vaan and Joerg Brambring.[116] The combination of such reflective polarizers, and LED dynamic backlight control[100] make today's LCD televisions far more efficient than the CRT-based sets, leading to a worldwide energy saving of 600 TWh (2017), equal to 10% of the electricity consumption of all households worldwide or equal to 2 times the energy production of all solar cells in the world.[117][118]

The first color LCD televisions were developed as handheld televisions in Japan. In 1980, Hattori Seiko's R&D group began development on color LCD pocket televisions.[61] In 1982, Seiko Epson released the first LCD television, the Epson TV Watch, a wristwatch equipped with a small active-matrix LCD television.[62][63] Sharp Corporation introduced dot matrix TN-LCD in 1983.[52] In 1984, Epson released the ET-10, the first full-color, pocket LCD television.[64] The same year, Citizen Watch,[65] introduced the Citizen Pocket TV,[61] a 2.7-inch color LCD TV,[65] with the first commercial TFT LCD.[61] In 1988, Sharp demonstrated a 14-inch, active-matrix, full-color, full-motion TFT-LCD. This led to Japan launching an LCD industry, which developed large-size LCDs, including TFT computer monitors and LCD televisions.[66] Epson developed the 3LCD projection technology in the 1980s, and licensed it for use in projectors in 1988.[67] Epson's VPJ-700, released in January 1989, was the world's first compact, full-color LCD projector.[63]

Hitachi also improved the viewing angle dependence further by optimizing the shape of the electrodes (Super IPS). NEC and Hitachi become early manufacturers of active-matrix addressed LCDs based on the IPS technology. This is a milestone for implementing large-screen LCDs having acceptable visual performance for flat-panel computer monitors and television screens. In 1996, Samsung developed the optical patterning technique that enables multi-domain LCD. Multi-domain and In Plane Switching subsequently remain the dominant LCD designs through 2006.[75] In the late 1990s, the LCD industry began shifting away from Japan, towards South Korea and Taiwan,[66] and later on towards China.

Kondakov DY . Characterization of triplet-triplet annihilation in organic light-emitting diodes based on anthracene derivatives. J Appl Phys 2007; 102: 114504.

What is lcd tftvstft

In 1983, researchers at Brown, Boveri & Cie (BBC) Research Center, Switzerland, invented the super-twisted nematic (STN) structure for passive matrix-addressed LCDs. H. Amstutz et al. were listed as inventors in the corresponding patent applications filed in Switzerland on July 7, 1983, and October 28, 1983. Patents were granted in Switzerland CH 665491, Europe EP 0131216,[58] U.S. patent 4,634,229 and many more countries. In 1980, Brown Boveri started a 50/50 joint venture with the Dutch Philips company, called Videlec.[59] Philips had the required know-how to design and build integrated circuits for the control of large LCD panels. In addition, Philips had better access to markets for electronic components and intended to use LCDs in new product generations of hi-fi, video equipment and telephones. In 1984, Philips researchers Theodorus Welzen and Adrianus de Vaan invented a video speed-drive scheme that solved the slow response time of STN-LCDs, enabling high-resolution, high-quality, and smooth-moving video images on STN-LCDs.[citation needed] In 1985, Philips inventors Theodorus Welzen and Adrianus de Vaan solved the problem of driving high-resolution STN-LCDs using low-voltage (CMOS-based) drive electronics, allowing the application of high-quality (high resolution and video speed) LCD panels in battery-operated portable products like notebook computers and mobile phones.[60] In 1985, Philips acquired 100% of the Videlec AG company based in Switzerland. Afterwards, Philips moved the Videlec production lines to the Netherlands. Years later, Philips successfully produced and marketed complete modules (consisting of the LCD screen, microphone, speakers etc.) in high-volume production for the booming mobile phone industry.

Furno M, Meerheim R, Hofmann S, Lüssem B, Leo K . Efficiency and rate of spontaneous emission in organic electroluminescent devices. Phys Rev B 2012; 85: 115205.

HDR is an emerging technology that can significantly improve picture quality158, 159, 160. However, strictly speaking, HDR is not a single metric; instead, it is more like a technical standard or a format (e.g., HDR10, Dolby Vision, etc.), unifying the aforementioned metrics. In general, HDR requires a higher CR (CR≥100 000:1), deeper dark state, higher peak brightness, richer grayscale (≥10 bits) and more vivid color.

where Tf is the frame time (e.g., Tf=16.67 ms for 60 fps). Using this equation, we can easily obtain an MPRT as long as the LC response time and TFT frame rate are known. The results are plotted in Figure 5.

Lewis JS, Weaver MS . Thin-film permeation-barrier technology for flexible organic light-emitting devices. IEEE J Sel Top Quantum Electron 2004; 10: 45–57.

Jiao MZ, Ge ZB, Wu ST, Choi WK . Submillisecond response nematic liquid crystal modulators using dual fringe field switching in a vertically aligned cell. Appl Phys Lett 2008; 92: 111101.

To further enhance the lifetime of the blue OLED, the NTU group has developed new ETL and TTF-EML materials together with an optimized layer structure and double EML structure104. Figure 10a shows the luminance decay curves of such a blue OLED under different initial luminance values (5000, 10 000, and 15 000 nits). From Figure 10b, the estimated T50 at 1000 nits of this blue OLED is ~56 000 h (~6–7 years)104, 105. As new materials and novel device structures continue to advance, the lifetime of OLEDs will be gradually improved.

Xie RJ, Hirosaki N, Takeda T . Wide color gamut backlight for liquid crystal displays using three-band phosphor-converted white light-emitting diodes. Appl Phys Express 2009; 2: 022401.

Li YW, Lin CW, Chen KY, Fan-Chiang KH, Kuo HC et al. Front-lit LCOS for wearable applications. SID Symp Dig Tech Pap 2014; 45: 234–236.

As Figure 6 depicts, there are two types of surface reflections. The first one is from a direct light source, i.e., the sun or a light bulb, denoted as A1. Its reflection is fairly specular, and in practice, we can avoid this reflection (i.e., strong glare from direct sun) by simply adjusting the display position or viewing direction. However, the second reflection, denoted as A2, is quite difficult to avoid. It comes from an extended background light source, such as a clear sky or scattered ceiling light. In our analysis, we mainly focus on the second reflection (A2).

Greinert N, Schoenefeld C, Suess P, Klasen-Memmer M, Bremer M et al. Opening the door to new LCD applications via polymer walls. SID Symp Dig Tech Pap 2015; 46: 382–385.

The two leading flat-panel display technologies—liquid crystal displays and organic light-emitting diode displays—have been compared. Liquid crystal displays (LCDs) currently have the upper hand, but organic light-emitting diode (OLED) technology is rapidly catching up. Shin-Tson Wu of the University of Central Florida and colleagues have documented recent material and design advances in these two technologies and analyzed display performance with respect to six key metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility. They concluded that LCDs are superior in terms of cost, lifetime and brightness, whereas OLED displays offer better black states, flexibility, and faster response times. The technologies have similar ambient contrast ratio, image motion blur, color gamut, viewing angle and power consumption. Emerging applications include virtual and augmented reality wearable displays as well as displays with high dynamic ranges.

Xiang CY, Guo JX, Sun XW, Yin XJ, Qi GJ . A fast response, three-electrode liquid crystal device. Jpn J Appl Phys 2003; 42: 763.

A fast response time helps to mitigate motion image blur and boost the optical efficiency, but this statement is only qualitatively correct. When quantifying the visual performance of a moving object, motion picture response time (MPRT) is more representative, and the following equation should be used53, 54, 55, 56, 57, 58:

Tan GJ, Lee YH, Gou FW, Hu MG, Lan YF et al. Macroscopic model for analyzing the electro-optics of uniform lying helix cholesteric liquid crystals. J Appl Phys 2017; 121: 173102.

Critics of the report point out that it assumes that all of the NF3 produced would be released to the atmosphere. In reality, the vast majority of NF3 is broken down during the cleaning processes; two earlier studies found that only 2 to 3% of the gas escapes destruction after its use.[176] Furthermore, the report failed to compare NF3's effects with what it replaced, perfluorocarbon, another powerful greenhouse gas, of which anywhere from 30 to 70% escapes to the atmosphere in typical use.[176]

For mobile displays, such as smartphones, touch functionality is required. Thus the outer surface is often subject to fingerprints, grease and other contaminants. Therefore, only a simple grade AR coating is used, and the total surface reflectance amounts to ~4.4%. Let us use the FFS LCD as an example for comparison with an OLED. The following parameters are used in our simulations: the LCD peak brightness is 600 nits and CR is 2000:1, while the OLED peak brightness is 500 nits and CR is infinity. Figure 8a depicts the calculated results, where the intersection occurs at 107 lux, which corresponds to a very dark overcast day. If the newly proposed structure with an in-cell polarizer is used, the FFS LCD could attain a 3000:1 CR69. In that case, the intersection is decreased to 72 lux (Figure 8b), corresponding to an office building hallway or restroom lighting. For reference, a typical office light is in the range of 320–500 lux70. As Figure 8 depicts, OLEDs have a superior ACR under dark ambient conditions, but this advantage gradually diminishes as the ambient light increases. This was indeed experimentally confirmed by LG Display71. Display brightness and surface reflection have key roles in the sunlight readability of a display device.

Yamamoto E, Yui H, Katsuta S, Asaoka Y, Maeda T et al. Wide viewing LCDs using novel microstructure film. SID Symp Dig Tech Pap 2014; 45: 385–388.

Gao YT, Luo ZY, Zhu RD, Hong Q, Wu ST et al. A high performance single-domain LCD with wide luminance distribution. J Display Technol 2015; 11: 315–324.

In 2004, researchers at the University of Oxford demonstrated two new types of zero-power bistable LCDs based on Zenithal bistable techniques.[156] Several bistable technologies, like the 360° BTN and the bistable cholesteric, depend mainly on the bulk properties of the liquid crystal (LC) and use standard strong anchoring, with alignment films and LC mixtures similar to the traditional monostable materials. Other bistable technologies, e.g., BiNem technology, are based mainly on the surface properties and need specific weak anchoring materials.

What is lcd tftdisplay

Flexible displays have a long history and have been attempted by many companies, but this technology has only recently begun to see commercial implementations for consumer electronics135. A good example is Samsung’s flagship smartphone, the Galaxy S series, which has an OLED display panel that covers the edge of the phone. However, strictly speaking, it is a curved display rather than a flexible display. One step forward, a foldable AM-OLED has been demonstrated with the curvature radius of 2 mm for 100 000 repeated folds136. Owing to the superior flexibility of the organic materials, a rollable AM-OLED display driven by an organic TFT was fabricated137. By replacing the brittle indium-tin-oxide with a flexible Ag nanowire as the anode, a stretchable OLED for up to a 120% strain was demonstrated138.

Yao L, Langguth N, Schroth D, Maisch R . Driving forces-how mobility of tomorrow influences technologies of today. SID Symp Dig Tech Pap 2017; 48: 775–778.

Schadt M . Milestone in the history of field-effect liquid crystal displays and materials. Jpn J Appl Phys 2009; 48: 03B001.

Peng FL, Chen HW, Gou FW, Lee YH, Wand M et al. Analytical equation for the motion picture response time of display devices. J Appl Phys 2017; 121: 023108.

The power efficiency of an OLED is generally limited by the extraction efficiency (ηext~20%). To improve the power efficiency, multiple approaches can be used, such as a microlens array, a corrugated structure with a high refractive index substrate107, replacing the metal electrode (such as the Al cathode) with a transparent metal oxide108, increasing the distance from the emission dipole to the metal electrode109 or increasing the carrier concentration by material optimizations110. Experimentally, external quantum efficiencies as high as 63% have been demonstrated107, 108. Note that sometimes the light-extraction techniques result in haze and image blur, which deteriorate the ACR and display sharpness111, 112, 113. Additionally, fabrication complexity and production yield are two additional concerns. Figure 11 shows the power efficiencies of white, green, red and blue phosphorescent as well as blue fluorescent/TTF OLEDs over time. For OLEDs with fluorescent emitters in the 1980s and 1990s, the power efficiency was limited by the IQE, typically <10 lm W−1(Refs. 41, 114, 115, 116, 117, 118). With the incorporation of phosphorescent emitters in the ~2000 s, the power efficiency was significantly improved owing to the materials and device engineering45, 119, 120, 121, 122, 123, 124, 125. The photonic design of OLEDs with regard to the light extraction efficiency was taken into consideration for further enchantment of the power efficiency126, 127, 128, 129, 130. For a green OLED, a power efficiency of 290 lm W−1 was demonstrated in 2011 (Ref. 127), which showed a >100 × improvement compared with that of the basic two-layer device proposed in 1987 (1.5 lm W−1 in Ref. 41). A white OLED with a power efficiency >100 lm W−1 was also demonstrated, which was comparable to the power efficiency of a LCD backlight. For red and blue OLEDs, their power efficiencies are generally lower than that of the green OLED due to their lower photopic sensitivity function, and there is a tradeoff between color saturation and power efficiency. Note, we separated the performances of blue phosphorescent and fluorescent/TTF OLEDs. For the blue phosphorescent OLEDs, although the power efficiency can be as high as ~80 lm W−1, the operation lifetime is short and color is sky-blue. For display applications, the blue TTF OLED is the favored choice, with an acceptable lifetime and color but a much lower power efficiency (16 lm W−1) than its phosphorescent counterpart131, 132. Overall, over the past three decades (1987–2017), the power efficiency of OLEDs has improved dramatically, as Figure 11 shows.

The viewing angle is another important property that defines the viewing experience at large oblique angles, which is quite critical for multi-viewer applications. OLEDs are self-emissive and have an angular distribution that is much broader than that of LCDs. For instance, at a 30° viewing angle, the OLED brightness only decreases by 30%, whereas the LCD brightness decrease exceeds 50%. To widen an LCD’s viewing angle, three options can be used. (1) Remove the brightness-enhancement film in the backlight system. The tradeoff is decreased on-axis brightness147. (2) Use a directional backlight with a front diffuser148, 149. Such a configuration enables excellent image quality regardless of viewing angle; however, image blur induced by a strong diffuser should be carefully treated. (3) Use QD arrays as the color filters20, 150, 151, 152. This design produces an isotropic viewing cone and high-purity RGB colors. However, preventing ambient light excitation of QDs remains a technical challenge20.

Mori H, Itoh Y, Nishiura Y, Nakamura T, Shinagawa Y . Performance of a novel optical compensation film based on negative birefringence of discotic compound for wide-viewing-angle twisted-nematic liquid-crystal displays. Jpn J Appl Phys 1997; 36: 143–147.

Bourzac K . Quantum dots go on display: adoption by TV makers could expand the market for light-emitting nanocrystals. Nature 2013; 493: 283.

Transmission spectra of color filters and emission spectra of (a) YAG WLED, (b) KSF WLED, (c) QDEF and (d) Vivid Color LED. KSF, potassium silicofluoride; QDEF, quantum dot enhancement film; WLED, white light-emitting diode; YAG, yttrium aluminum garnet.

Chen HF, Ha TH, Sung JH, Kim HR, Han BH . Evaluation of LCD local-dimming-backlight system. J Soc Inf Display 2010; 18: 57–65.

Daly S, Kunkel T, Sun X, Farrell S, Crum P . Viewer preferences for shadow, diffuse, specular, and emissive luminance limits of high dynamic range displays. SID Symp Dig Tech Pap 2013; 44: 563–566.

The chemical formula of the liquid crystals used in LCDs may vary. Formulas may be patented.[4] An example is a mixture of 2-(4-alkoxyphenyl)-5-alkylpyrimidine with cyanobiphenyl, patented by Merck and Sharp Corporation. The patent that covered that specific mixture has expired.[5]

LCDs are available to display arbitrary images (as in a general-purpose computer display) or fixed images with low information content, which can be displayed or hidden: preset words, digits, and seven-segment displays (as in a digital clock) are all examples of devices with these displays. They use the same basic technology, except that arbitrary images are made from a matrix of small pixels, while other displays have larger elements.

Takeda A, Kataoka S, Sasaki T, Chida H, Tsuda H et al. A super-high image quality multi-domain vertical alignment LCD by new rubbing-less technology. SID Symp Dig Tech Pap 1998; 29: 1077–1080.

Chen HW, Zhu RD, Li MC, Lee SL, Wu ST . Pixel-by-pixel local dimming for high-dynamic-range liquid crystal displays. Opt Express 2017; 25: 1973–1984.

Twisted nematic displays contain liquid crystals that twist and untwist at varying degrees to allow light to pass through. When no voltage is applied to a TN liquid crystal cell, polarized light passes through the 90-degrees twisted LC layer. In proportion to the voltage applied, the liquid crystals untwist changing the polarization and blocking the light's path. By properly adjusting the level of the voltage almost any gray level or transmission can be achieved.

Geffroy B, Le Roy P, Prat C . Organic light‐emitting diode (OLED) technology: materials, devices and display technologies. Polym Int 2006; 55: 572–582.

ITU. Parameter Values for the HDTV Standards for Production and International Programme Exchange. Geneva, Switzerland: ITU; 2002 ITU-R Recommendation BT.709-5.

Sun YR, Forrest SR . High-efficiency white organic light emitting devices with three separate phosphorescent emission layers. Appl Phys Lett 2007; 91: 263503.

Today, most LCD screens are being designed with an LED backlight instead of the traditional CCFL backlight, while that backlight is dynamically controlled with the video information (dynamic backlight control). The combination with the dynamic backlight control, invented by Philips researchers Douglas Stanton, Martinus Stroomer and Adrianus de Vaan, simultaneously increases the dynamic range of the display system (also marketed as HDR, high dynamic range television or FLAD, full-area local area dimming).[109][110][100]

The basic structure of an OLED display, proposed by Tang and VanSlyke41 in 1987, consists of organic stacks sandwiched between anode and cathode, as shown in Figure 3a. Electrons and holes are injected from electrodes to organic layers for recombination and light emission; hence, an OLED display is an emissive display, unlike an LCD. Currently, multi-layer structures in OLEDs with different functional materials are commonly used, as shown in Figure 3b. The emitting layer (EML), which is used for light emission, consists of dopant and host materials with high quantum efficiency and high carrier mobility. Hole-transporting layer (HTL) and electron-transporting layer (ETL) between the EML and electrodes bring carriers into the EML for recombination. Hole- and electron-injection layers (HIL and EIL) are inserted between the electrodes and the HTL and ETL interface to facilitate carrier injection from the conductors to the organic layers. When applying voltage to the OLED, electrons and holes supplied from the cathode and anode, respectively, transport to the EML for recombination to give light.

Calculated ACR as a function of different ambient light conditions for LCD and OLED TVs. Here we assume that the LCD peak brightness is 1200 nits and OLED peak brightness is 600 nits, with a surface reflectance of 1.2% for both the LCD and OLED. (a) LCD CR: 5000:1, OLED CR: infinity; (b) LCD CR: 20 000:1, OLED CR: infinity.

The EML is the core of an OLED. Based on the emitters inside, OLED devices can be categorized into four types: fluorescence, triplet-triplet fluorescence (TTF), phosphorescence, and thermally activated delayed fluorescence (TADF)41, 44, 45, 46, 47.

In 2016, Panasonic developed IPS LCDs with a contrast ratio of 1,000,000:1, rivaling OLEDs. This technology was later put into mass production as dual layer, dual panel or LMCL (Light Modulating Cell Layer) LCDs. The technology uses 2 liquid crystal layers instead of one, and may be used along with a mini-LED backlight and quantum dot sheets.[83][84]

Hack M, Weaver MS, Brown JJ . Status and opportunities for phosphorescent OLED lighting. SID Symp Dig Tech Pap 2017; 48: 187–190.

As these new applications are emerging, LCDs and OLEDs have new opportunities as well as new challenges. Let us take a vehicle display as an example: high brightness, good sunlight readability, and a wide working temperature range are required184. To follow this trend, LC mixtures with an ultra-high clearing temperature (>140 °C) have been recently developed, ensuring that the LCD works properly even at some extreme temperatures185. OLEDs have an attractive form factor for vehicle displays, but their performance needs to qualify under the abovementioned harsh working conditions. Similarly, for transparent displays or mirror displays, LCDs and OLEDs have their own merits and demerits186, 187, 188, 189. They should aim at versatile functions based on their own strengths.

Zhu RD, Chen HW, Wu ST . Achieving 12-bit perceptual quantizer curve with liquid crystal display. Opt Express 2017; 25: 10939–10946.

Lee C, Kim JJ . Enhanced light out-coupling of OLEDs with low haze by inserting randomly dispersed nanopillar arrays formed by lateral phase separation of polymer blends. Small 2013; 9: 3858–3863.

Kim SS, You BH, Cho JH, Kim DG, Berkeley BH et al. An 82-in. ultra-definition 120-Hz LCD TV using new driving scheme and advanced Super PVA technology. J Soc Inf Display 2009; 17: 71–78.

Tanaka D, Sasabe H, Li YJ, Su SJ, Takeda T et al. Ultra high efficiency green organic light-emitting devices. Jpn J Appl Phys 2007; 46: L10–L12.

Kimura K, Onoyama Y, Tanaka T, Toyomura N, Kitagawa H . New pixel driving circuit using self-discharging compensation method for high- resolution OLED micro displays on a silicon backplane. J Soc Inf Display 2017; 25: 167–176.

Chen HW, Zhu RD, Käläntär K, Wu ST . Quantum dot-enhanced LCDs with wide color gamut and broad angular luminance distribution. SID Symp Dig Tech Pap 2016; 47: 1413–1416.

In-plane switching is an LCD technology that aligns the liquid crystals in a plane parallel to the glass substrates. In this method, the electrical field is applied through opposite electrodes on the same glass substrate, so that the liquid crystals can be reoriented (switched) essentially in the same plane, although fringe fields inhibit a homogeneous reorientation. This requires two transistors for each pixel instead of the single transistor needed for a standard thin-film transistor (TFT) display. The IPS technology is used in everything from televisions, computer monitors, and even wearable devices, especially almost all LCD smartphone panels are IPS/FFS mode. IPS displays belong to the LCD panel family screen types. The other two types are VA and TN. Before LG Enhanced IPS was introduced in 2001 by Hitachi as 17" monitor in Market, the additional transistors resulted in blocking more transmission area, thus requiring a brighter backlight and consuming more power, making this type of display less desirable for notebook computers. Panasonic Himeji G8.5 was using an enhanced version of IPS, also LGD in Korea, then currently the world biggest LCD panel manufacture BOE in China is also IPS/FFS mode TV panel.

Levermore P, Schenk T, Tseng HR, Wang HJ, Heil H et al. Ink-jet-printed OLEDs for display applications. SID Symp Dig Tech Pap 2016; 47: 484–486.

Yu IH, Song IS, Lee JY, Lee SH . Intensifying the density of a horizontal electric field to improve light efficiency in a fringe-field switching liquid crystal display. J Phys D Appl Phys 2006; 39: 2367–2372.

Schematic diagram of the (a) TN mode, (b) VA mode, (c) IPS mode and (d) FFS mode. The LC director orientations are shown in the voltage-off (left) and voltage-on (right) states.

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LCDs are manufactured in cleanrooms borrowing techniques from semiconductor manufacturing and using large sheets of glass whose size has increased over time. Several displays are manufactured at the same time, and then cut from the sheet of glass, also known as the mother glass or LCD glass substrate. The increase in size allows more displays or larger displays to be made, just like with increasing wafer sizes in semiconductor manufacturing. The glass sizes are as follows:

VA was first invented in 1971 by Schiekel and Fahrenschon14 but did not receive widespread attention until the late 1990s, when multi-domain VA (MVA) mode was proposed to solve the viewing angle problem26, 27, 28. In the VA mode, an LC with a negative Δɛ<0 is used and the electric field is in the longitudinal direction. In the initial state (V=0), the LC directors are aligned in the vertical direction (Figure 2b). As the voltage exceeds a threshold, the LC directors are gradually tilted so that the incident light transmits through the crossed polarizers. Film-compensated MVA mode has a high on-axis contrast ratio (CR; >5000:1), wide viewing angle and fairly fast response time (5 ms). Thus it is widely used in large TVs29, 30. Recently, curved MVA LCD TVs have become popular because VA mode enables the smallest bending curvature compared with other LCDs31, 32.

FFS mode was proposed in 1998 by three Korean scientists: SH Lee, SL Lee, and HY Kim21. Soon after its invention, FFS became a popular LCD mode due to its outstanding features, including high transmittance, wide viewing angle, weak color shift, built-in storage capacitance, and robustness to touch pressure35, 36, 37. Basically, FFS shares a similar working principle with IPS, but the pixel and common electrodes are separated by a thin passivation layer (Figure 2d). As a result, the electrode width and gap are able to be much smaller than those of IPS, leading to much stronger fringe fields covering both the electrode and gap regions. Thus the dead zone areas are reduced. In general, both positive (p-FFS) and negative (n-FFS) Δɛ LCs can be used in the FFS mode38, 39. Currently, n-FFS is preferred for mobile applications because its transmittance is higher than that of p-FFS (98 vs. 88%)40.

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In 1888,[29] Friedrich Reinitzer (1858–1927) discovered the liquid crystalline nature of cholesterol extracted from carrots (that is, two melting points and generation of colors) and published his findings.[30] In 1904, Otto Lehmann published his work "Flüssige Kristalle" (Liquid Crystals). In 1911, Charles Mauguin first experimented with liquid crystals confined between plates in thin layers.

Two triplet excitons may fuse to form one singlet exciton through the so-called triplet fusion process, as shown in Figure 4b, and relaxes to the energy from the singlet state, called TTF, which improves the theoretical limit of the IQE to 62.5%.

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Schematic diagram of an OLED. (a) Basic structure proposed by Tang and VanSlyke in 1987. (b) Multi-layer structure employed in current OLED products. EIL, electron-injection layer; ETL, electron-transporting layer; EML, emitting layer; HTL, hole-transporting layer; HIL, hole-injection layer.

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In addition to brightness, color, grayscale and the CR also vary with the viewing angle, known as color shift and gamma shift. In these aspects, LCDs and OLEDs have different mechanisms. For LCDs, they are induced by the anisotropic property of the LC material, which could be compensated for with uniaxial or biaxial films5. For OLEDs, they are caused by the cavity effect and color-mixing effect153, 154. With extensive efforts and development, both technologies have fairly mature solutions; currently, color shift and gamma shift have been minimized at large oblique angles.

Kim KH, Liao JL, Lee SW, Sim B, Moon CK et al. Crystal organic light-emitting diodes with perfectly oriented non-doped Pt-based emitting layer. Adv Mater 2016; 28: 2526–2532.

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With the introduction of heavy metal atoms (such as Ir and Pt) into the emitters, strong spin-orbital coupling greatly reduces the triplet lifetime to ~μs, which results in efficient phosphorescent emission. The singlet exciton experiences intersystem crossing to the triplet state for light emission, achieving a 100% IQE, as shown in Figure 4c. Owing to the long radiative lifetime (~μs) in a phosphorescent OLED, the triplet may interact with another triplet and polaron (triplet-triplet annihilation and triplet-polaron annihilation, respectively), which results in efficiency roll-off under high current driving48. Such processes may create hot excitons and hot polarons to shorten the operation lifetime, especially for blue-emitting devices, as will be discussed in the next section49.

Kim HJ, Shin MH, Lee JY, Kim JH, Kim YJ . Realization of 95% of the Rec. 2020 color gamut in a highly efficient LCD using a patterned quantum dot film. Opt Express 2017; 25: 10724–10734.

(a) Luminance decay curves for the blue OLED with different initial luminance values. (b) Estimated T50 under different initial luminance values.

In 2011, LG claimed the smartphone LG Optimus Black (IPS LCD (LCD NOVA)) has the brightness up to 700 nits, while the competitor has only IPS LCD with 518 nits and double an active-matrix OLED (AMOLED) display with 305 nits. LG also claimed the NOVA display to be 50 percent more efficient than regular LCDs and to consume only 50 percent of the power of AMOLED displays when producing white on screen.[142] When it comes to contrast ratio, AMOLED display still performs best due to its underlying technology, where the black levels are displayed as pitch black and not as dark gray. On August 24, 2011, Nokia announced the Nokia 701 and also made the claim of the world's brightest display at 1000 nits. The screen also had Nokia's Clearblack layer, improving the contrast ratio and bringing it closer to that of the AMOLED screens.

Zhu RD, Chen HW, Kosa T, Coutino P, Tan GJ et al. High-ambient-contrast augmented reality with a tunable transmittance liquid crystal film and a functional reflective polarizer. J Soc Inf Display 2016; 24: 229–233.

Samsung introduced UFB (Ultra Fine & Bright) displays back in 2002, utilized the super-birefringent effect. It has the luminance, color gamut, and most of the contrast of a TFT-LCD, but only consumes as much power as an STN display, according to Samsung. It was being used in a variety of Samsung cellular-telephone models produced until late 2006, when Samsung stopped producing UFB displays. UFB displays were also used in certain models of LG mobile phones.

Chen PY, Chen CL, Chen CC, Tsai L, Ting HC et al. 65-inch inkjet printed organic light-emitting display panel with high degree of pixel uniformity. SID Symp Dig Tech Pap 2014; 45: 396–398.

The peak brightness of LCDs could be boosted to 2000 nits or even higher by simply using a high-power backlight. OLEDs are self-emissive, so their peak brightness would trade with lifetime. As a result, more advanced OLED materials and novel structural designs are highly desirable in the future. Another reason to boost peak brightness is to increase sunlight readability. Especially for some outdoor applications, such as public displays, peak brightness is critical to ensure good readability under strong ambient light. As discussed in the section of ‘CR and ACR’, high brightness leads to a high ACR, except that the power consumption will increase.

In practical applications, red and green phosphorescent emitters are the mainstream for active matrix (AM) OLEDs due to their high IQE. While, for blue emitters, TTF is mostly used because of its longer operation lifetime51. However, recently, TADF materials have been rapidly emerging and are expected to have widespread applications in the near future.

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A standard television receiver screen, a modern LCD panel, has over six million pixels, and they are all individually powered by a wire network embedded in the screen. The fine wires, or pathways, form a grid with vertical wires across the whole screen on one side of the screen and horizontal wires across the whole screen on the other side of the screen. To this grid each pixel has a positive connection on one side and a negative connection on the other side. So the total amount of wires needed for a 1080p display is 3 x 1920 going vertically and 1080 going horizontally for a total of 6840 wires horizontally and vertically. That's three for red, green and blue and 1920 columns of pixels for each color for a total of 5760 wires going vertically and 1080 rows of wires going horizontally. For a panel that is 28.8 inches (73 centimeters) wide, that means a wire density of 200 wires per inch along the horizontal edge.

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In October 2011, Toshiba announced 2560 × 1600 pixels on a 6.1-inch (155 mm) LCD panel, suitable for use in a tablet computer,[81] especially for Chinese character display. The 2010s also saw the wide adoption of TGP (Tracking Gate-line in Pixel), which moves the driving circuitry from the borders of the display to in between the pixels, allowing for narrow bezels.[82]

As summarized in Table 1, these four LCD modes have their own unique features and are used for different applications. For example, TN has the advantages of low cost and high optical efficiency; thus, it is mostly used in wristwatches, signage and laptop computers, for which a wide view is not absolutely necessary. MVA mode is particularly attractive for large TVs because a fast response time, high CR and wide viewing angle are required to display motion pictures. On the other hand, IPS and FFS modes are used in mobile displays, where low power consumption for a long battery life and pressure resistance for touch screens are critical.

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To compare the power consumption of LCDs and OLEDs with the same resolution density, the displayed contents should be considered as well. In general, OLEDs are more efficient than LCDs for displaying dark images because black pixels consume little power for an emissive display, while LCDs are more efficient than OLEDs at displaying bright images. Currently, a ~65% average picture level is the intersection point between RGB OLEDs and LCDs134. For color-filter-based white OLED TVs, this intersection point drops to ~30%. As both technologies continue to advance, the crossover point will undoubtedly change with time.

To investigate the ACR, we have to clarify the reflectance first. A large TV is often operated by remote control, so touchscreen functionality is not required. As a result, an anti-reflection coating is commonly adopted. Let us assume that the reflectance is 1.2% for both LCD and OLED TVs. For the peak brightness and CR, different TV makers have their own specifications. Here, without losing generality, let us use the following brands as examples for comparison: LCD peak brightness=1200 nits, LCD CR=5000:1 (Sony 75″ X940E LCD TV); OLED peak brightness=600 nits, and OLED CR=infinity (Sony 77″ A1E OLED TV). The obtained ACR for both LCD and OLED TVs is plotted in Figure 7a. As expected, OLEDs have a much higher ACR in the low illuminance region (dark room) but drop sharply as ambient light gets brighter. At 63 lux, OLEDs have the same ACR as LCDs. Beyond 63 lux, LCDs take over. In many countries, 60 lux is the typical lighting condition in a family living room. This implies that LCDs have a higher ACR when the ambient light is brighter than 60 lux, such as in office lighting (320–500 lux) and a living room with the window shades or curtain open. Please note that, in our simulation, we used the real peak brightness of LCDs (1200 nits) and OLEDs (600 nits). In most cases, the displayed contents could vary from black to white. If we consider a typical 50% average picture level (i.e., 600 nits for LCDs vs. 300 nits for OLEDs), then the crossover point drops to 31 lux (not shown here), and LCDs are even more favorable. This is because the on-state brightness plays an important role to the ACR, as Equation (2) shows.

Recently, an LCD panel with an in-cell polarizer was proposed to decouple the depolarization effect of the LC layer and color filters69. Thus the light leakage was able to be suppressed substantially, leading to a significantly enhanced CR. It has been reported that the CR of a VA LCD could be boosted to 20 000:1. Then we recalculated the ACR, and the results are shown in Figure 7b. Now, the crossover point takes place at 16 lux, which continues to favor LCDs.

The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968.[42] Lechner, F.J. Marlowe, E.O. Nester and J. Tults demonstrated the concept in 1968 with an 18x2 matrix dynamic scattering mode (DSM) LCD that used standard discrete MOSFETs.[43]

The optical effect of a TN device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, TN displays with low information content and no backlighting are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). As most of 2010-era LCDs are used in television sets, monitors and smartphones, they have high-resolution matrix arrays of pixels to display arbitrary images using backlighting with a dark background. When no image is displayed, different arrangements are used. For this purpose, TN LCDs are operated between parallel polarizers, whereas IPS LCDs feature crossed polarizers. In many applications IPS LCDs have replaced TN LCDs, particularly in smartphones. Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).

Some of these issues relate to full-screen displays, others to small displays as on watches, etc. Many of the comparisons are with CRT displays.

Chen HW, Peng FL, Gou FW, Lee YH, Wand M et al. Nematic LCD with motion picture response time comparable to organic LEDs. Optica 2016; 3: 1033–1034.

Vertical-alignment displays are a form of LCDs in which the liquid crystals naturally align vertically to the glass substrates. When no voltage is applied, the liquid crystals remain perpendicular to the substrate, creating a black display between crossed polarizers. When voltage is applied, the liquid crystals shift to a tilted position, allowing light to pass through and create a gray-scale display depending on the amount of tilt generated by the electric field. It has a deeper-black background, a higher contrast ratio, a wider viewing angle, and better image quality at extreme temperatures than traditional twisted-nematic displays.[148] Compared to IPS, the black levels are still deeper, allowing for a higher contrast ratio, but the viewing angle is narrower, with color and especially contrast shift being more apparent, and the cost of VA is lower than IPS (but higher than TN).[149]

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The energy between the singlet and triplet can be reduced (<0.1 eV) by minimizing the exchange energy50; thus the triplet can jump back to the singlet state by means of thermal energy (reverse intersystem crossing) for fluorescence emission, which is called TADF, as shown in Figure 4d. Achieving a 100% IQE is possible for TADF emission without a heavy atom in the organic material, which reduces the material cost and is more flexible for organic molecular design.

In this review paper, we present recent progress on LCDs and OLEDs regarding materials, device structures to final panel performances. First, in Section II, we briefly describe the device configurations and operation principles of these two technologies. Then, in Section III, we choose six key metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility, to evaluate LCDs and OLEDs. Their future perspectives are discussed in Section IV, including high dynamic range (HDR), virtual reality/augmented reality (VR/AR) and smart displays with versatile functions.

For conventional LCDs employing a WLED backlight, the yellow spectrum generated by YAG (yttrium aluminum garnet) phosphor is too broad to become highly saturated RGB primary colors, as shown in Figure 9a77. As a result, the color gamut is only ~50% Rec. 2020. To improve the color gamut, more advanced backlight units have been developed, as summarized in Table 2. The first choice is the RG-phosphor-converted WLED78, 79. From Figure 9b, the red and green emission spectra are well separated; still, the green spectrum (generated by β-sialon:Eu2+ phosphor) is fairly broad and red spectrum (generated by K2SiF6:Mn4+ (potassium silicofluoride, KSF) phosphor) is not deep enough, leading to 70%–80% Rec. 2020, depending on the color filters used.

Huang YG, Chen HW, Tan GJ, Tobata H, Yamamoto SI et al. Optimized blue-phase liquid crystal for field-sequential-color displays. Opt Mater Express 2017; 7: 641–650.

Power efficiency of white, red, green and phosphorescent blue and fluorescent/TTF blue OLEDs over time. Data are compiled from Refs. 41, 45, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133.

Wyatt D, Chen HW, Wu ST . Wide-color-gamut LCDs with vivid color LED technology. SID Symp Dig Tech Pap 2017; 48: 992–995.

LCDs with quantum dot enhancement film or quantum dot color filters were introduced from 2015 to 2018. Quantum dots receive blue light from a backlight and convert it to light that allows LCD panels to offer better color reproduction.[85][86][87][88][89][90] Quantum dot color filters are manufactured using photoresists containing quantum dots instead of colored pigments,[91] and the quantum dots can have a special structure to improve their application onto the color filter. Quantum dot color filters offer superior light transmission over quantum dot enhancement films.[92]

Yamazaki A, Wu CL, Cheng WC, Badano A . Spatial resolution characteristics of organic light-emitting diode displays: a comparative analysis of MTF for handheld and workstation formats. SID Symp Dig Tech Pap 2013; 44: 419–422.

Hsiao K, Tang GF, Yu G, Zhang ZW, Xu XJ et al. Development and analysis of technical challenges in the world's largest (110-in.) curved LCD. SID Symp Dig Tech Pap 2015; 46: 1059–1062.

Ishinabe T, Obonai Y, Fujikake H . A foldable ultra-thin LCD using a coat-debond polyimide substrate and polymer walls. SID Symp Dig Tech Pap 2016; 47: 83–86.

Monochrome and later color passive-matrix LCDs were standard in most early laptops (although a few used plasma displays[122][123]) and the original Nintendo Game Boy[124] until the mid-1990s, when color active-matrix became standard on all laptops. The commercially unsuccessful Macintosh Portable (released in 1989) was one of the first to use an active-matrix display (though still monochrome). Passive-matrix LCDs are still used in the 2010s for applications less demanding than laptop computers and TVs, such as inexpensive calculators. In particular, these are used on portable devices where less information content needs to be displayed, lowest power consumption (no backlight) and low cost are desired or readability in direct sunlight is needed.

Known as fringe field switching (FFS) until 2003,[143] advanced fringe field switching is similar to IPS or S-IPS offering superior performance and color gamut with high luminosity. AFFS was developed by Hydis Technologies Co., Ltd, Korea (formally Hyundai Electronics, LCD Task Force).[144] AFFS-applied notebook applications minimize color distortion while maintaining a wider viewing angle for a professional display. Color shift and deviation caused by light leakage is corrected by optimizing the white gamut which also enhances white/gray reproduction. In 2004, Hydis Technologies Co., Ltd licensed AFFS to Japan's Hitachi Displays. Hitachi is using AFFS to manufacture high-end panels. In 2006, HYDIS licensed AFFS to Sanyo Epson Imaging Devices Corporation. Shortly thereafter, Hydis introduced a high-transmittance evolution of the AFFS display, called HFFS (FFS+). Hydis introduced AFFS+ with improved outdoor readability in 2007. AFFS panels are mostly utilized in the cockpits of latest commercial aircraft displays. However, it is no longer produced as of February 2015.[145][146][147]

From Figure 5, we can gain several important physical insights: (1) Increasing the frame rate is a simple approach to suppress image motion blur, but its improvement gradually saturates. For example, if the LC response time is 10 ms, then increasing the frame rate from 30 to 60 fps would significantly reduce the MPRT. However, as the TFT frame rate continues to increase to 120 and 240 fps, then the improvement gradually saturates. (2) At a given frame rate, say 120 fps, as the LC response time decreases, the MPRT decreases almost linearly and then saturates. This means that the MPRT is mainly determined by the TFT frame rate once the LC response time is fast enough, i.e., τ≪Tf. Under such conditions, Equation (1) is reduced to MPRT≈0.8Tf. (3) When the LC response is <2 ms, its MPRT is comparable to that of an OLED at the same frame rate, e.g., 120 fps. Here we assume the OLED’s response time is 0.

An LCD’s resolution density is determined by the TFTs and color filter arrays. In SID 2017, Samsung demonstrated an LCD panel with a resolution of 2250 ppi for VR applications. The pitches of the sub-pixel and pixel are 3.76 and 11.28 μm, respectively. Meanwhile, field sequential color provides another promising option to triple the LCD resolution density168, 169. However, more advanced LC mixtures and fast response LCD modes are needed to suppress the color breakup issue170, 171, 172, 173, 174, 175, 176, 177, 178, 179. For OLED microdisplays, eMagin proposed a novel direct patterning approach to enable 2645 ppi RGB organic emitters on a CMOS backplane180. Similar performance has been obtained by Sony. They developed a 0.5-inch AM-OLED panel with 3200 ppi using well-controlled color filter arrays181.

Yoo O, Nam S, Choi J, Yoo S, Kim KJ et al. Contrast enhancement based on advanced local dimming system for high dynamic range LCDs. SID Symp Dig Tech Pap 2017; 48: 1667–1669.

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The next type of lifetime is operational lifetime. Owing to material degradation, OLED luminance will decrease and voltage will increase after long-term driving98. For red, yellow and green phosphorescent OLEDs, their lifetime values at 50% luminance decrease (T50) can be as long as >80 000 h with a 1000 cd m−2 luminance99, 100, 101. Nevertheless, the operational lifetime of the blue phosphor is far from satisfactory. Owing to the long exciton lifetime (~μs) and wide bandgap (~3 eV), triplet-polaron annihilation occurs in the blue phosphorescent OLED, which generates hot polarons (~6 eV; this energy is higher than some bond energies, e.g., 3.04 eV for the C-N single bond), leading to a short lifetime. To improve its lifetime, several approaches have been proposed, such as designing a suitable device structure to broaden the recombination zone, stacking two or three OLEDs or introducing an exciton quenching layer. The operation lifetime of a blue phosphorescent OLED can be improved to 3700 h (T50, half lifetime) with an initial luminance of 1000 nits. However, this is still ~20 × shorter than that of red and green phosphorescent OLEDs101, 102, 103.

Blue phase mode LCDs have been shown as engineering samples early in 2008, but they are not in mass-production. The physics of blue phase mode LCDs suggest that very short switching times (≈1 ms) can be achieved, so time sequential color control can possibly be realized and expensive color filters would be obsolete.[citation needed]

First, upon electrical excitation, 25% singlets and 75% triplets are formed with higher and lower energy, respectively. In a fluorescent OLED, only singlets decay radiatively through fluorescence with an ~ns exciton lifetime, which sets the theoretical limit of the internal quantum efficiency (IQE) to 25%, as shown in Figure 4a.

Komatsu R, Nakazato R, Sasaki T, Suzuki A, Senda N et al. Repeatedly foldable book-type AMOLED display. SID Symp Dig Tech Pap 2014; 45: 326–329.

Ghosh A, Donoghue EP, Khayrullin I, Ali T, Wacyk I et al. Directly patterened 2645 Ppi full color OLED microdisplay for head mounted wearables. SID Symp Dig Tech Pap 2016; 47: 837–840.

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What is TFTdisplay in mobile

Park JS, Chae H, Chung HK, Lee SI . Thin film encapsulation for flexible AM-OLED: a review. Semicond Sci Technol 2011; 26: 034001.

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LCDs do not produce light on their own, so they require external light to produce a visible image.[93][94] In a transmissive type of LCD, the light source is provided at the back of the glass stack and is called a backlight. Active-matrix LCDs are almost always backlit.[95][96] Passive LCDs may be backlit but many are reflective as they use a reflective surface or film at the back of the glass stack to utilize ambient light. Transflective LCDs combine the features of a backlit transmissive display and a reflective display.

Cost is another key factor for consumers. LCDs have been the topic of extensive investigation and investment, whereas OLED technology is emerging and its fabrication yield and capability are still far behind LCDs. As a result, the price of OLEDs is about twice as high as that of LCDs, especially for large displays. As more investment is made in OLEDs and more advanced fabrication technology is developed, such as ink-jet printing155, 156, 157, their price should decrease noticeably in the near future.

Display technology has gradually but profoundly shaped the lifestyle of human beings, which is widely recognized as an indispensable part of the modern world1. Presently, liquid crystal displays (LCDs) are the dominant technology, with applications spanning smartphones, tablets, computer monitors, televisions (TVs), to data projectors2, 3, 4, 5. However, in recent years, the market for organic light-emitting diode (OLED) displays has grown rapidly and has started to challenge LCDs in all applications, especially in the small-sized display market6, 7, 8. Lately, ‘LCD vs. OLED: who wins?’ has become a topic of heated debate9.

On December 4, 1970, the twisted nematic field effect (TN) in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261 Archived March 9, 2021, at the Wayback Machine) with Wolfgang Helfrich and Martin Schadt (then working for the Central Research Laboratories) listed as inventors.[35] Hoffmann-La Roche licensed the invention to Swiss manufacturer Brown, Boveri & Cie, its joint venture partner at that time, which produced TN displays for wristwatches and other applications during the 1970s for the international markets including the Japanese electronics industry, which soon produced the first digital quartz wristwatches with TN-LCDs and numerous other products. James Fergason, while working with Sardari Arora and Alfred Saupe at Kent State University Liquid Crystal Institute, filed an identical patent in the United States on April 22, 1971.[44] In 1971, the company of Fergason, ILIXCO (now LXD Incorporated), produced LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption. Tetsuro Hama and Izuhiko Nishimura of Seiko received a US patent dated February 1971, for an electronic wristwatch incorporating a TN-LCD.[45] In 1972, the first wristwatch with TN-LCD was launched on the market: The Gruen Teletime which was a four digit display watch.

LCDs are non-emissive, and their invention can be traced back to the 1960s and early 1970s10, 11, 12, 13, 14, 15. With extensive material research and development, device innovation and heavy investment on advanced manufacturing technologies, thin-film transistor (TFT) LCD technology has gradually matured in all aspects; some key hurdles, such as the viewing angle, response time and color gamut, have been overcome5. Compared with OLEDs, LCDs have advantages in lifetime, cost, resolution density and peak brightness16. On the other hand, OLEDs are emissive; their inherent advantages are obvious, such as true black state, fast response time and an ultra-thin profile, which enables flexible displays8, 9. As for color performance, OLEDs have a wider color gamut over LCDs employing a white light-emitting diode (WLED) as a backlight. Nevertheless, LCD with a quantum dot (QD) backlight has been developed and promoted17, 18, 19, 20. The full width at half maximum (FWHM) of green and red QDs is only 25 nm. As a result, a QD-enhanced LCD has a wider color gamut than an OLED. Generally speaking, both technologies have their own pros and cons. The competition is getting fierce; therefore, an objective systematic analysis and comparison on these two superb technologies is in great demand.

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Liquid crystal (LC) materials do not emit light; therefore, a backlight unit is usually needed (except in reflective displays) to illuminate the display panel. Figure 1 depicts an edge-lit TFT-LCD. The incident LED passes through the light-guide plate and multiple films and is then modulated by the LC layer sandwiched between two crossed polarizers5. In general, four popular LCD operation modes are used depending on the molecular alignments and electrode configurations: (1) twisted nematic (TN) mode, (2) vertical alignment (VA) mode, (3) in-plane switching (IPS) mode, and (4) fringe-field switching (FFS) mode13, 14, 15, 21. Below, we will briefly discuss each operation mode.

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Dead pixel policies are often hotly debated between manufacturers and customers. To regulate the acceptability of defects and to protect the end user, ISO released the ISO 13406-2 standard, which was made obsolete in 2008 with the release of ISO 9241, specifically ISO-9241-302, 303, 305, 307:2008 pixel defects. However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways. LCD panels are more likely to have defects than most ICs due to their larger size.[153]

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To evaluate the performance of display devices, several metrics are commonly used, such as response time, CR, color gamut, panel flexibility, viewing angle, resolution density, peak brightness, lifetime, among others. Here we compare LCD and OLED devices based on these metrics one by one.

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The color performance of a RGB OLED is mainly governed by the three independent RGB EMLs. Currently, both deep blue fluorescent OLEDs87 and deep red phosphorescent OLEDs88 have been developed. The corresponding color gamut is >90% Rec. 2020. Apart from material development89, the color gamut of OLEDs could also be enhanced by device optimization. For example, a strong cavity could be formed between a semitransparent and reflective layer. This selects certain emission wavelengths and hence reduces the FWHM90. However, the tradeoff is increased color shift at large viewing angles91.

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Vivid color is another critical requirement of all display devices72. Until now, several color standards have been proposed to evaluate color performance, including sRGB, NTSC, DCI-P3 and Rec. 202073, 74, 75, 76. It is believed that Rec. 2020 is the ultimate goal, and its coverage area in color space is the largest, nearly twice as wide as that of sRGB. However, at the present time, only RGB lasers can achieve this goal.

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LCDs can either be normally on (positive) or off (negative), depending on the polarizer arrangement. For example, a character positive LCD with a backlight has black lettering on a background that is the color of the backlight, and a character negative LCD has a black background with the letters being of the same color as the backlight.

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Both LCD and OLED are HDR-compatible. Currently, the best HDR LCDs can produce brighter highlights than OLEDs, but OLEDs have better overall CRs thanks to their superior black level. To enhance an LCD’s CR, a local dimming backlight is commonly used, but its dimming accuracy is limited by the number of LED segmentations161, 162, 163. Recently, a dual-panel LCD system was proposed for pixel-by-pixel local dimming164, 165. In an experiment, an exceedingly high CR (>1 000 000:1) and high bit-depth (>14 bits) were realized at merely 5 volts. In 2017, such a dual-panel LCD was demonstrated by Panasonic, aiming at medical and vehicular applications. At 2018 consumer electronics show, Innolux demonstrated a 10.1″ LCD with an active matrix mini-LED backlight. The size of each mini-LED is 1 mm and pitch length is 2 mm. In total, there are 6720 local dimming zones. Such a mini-LED based LCD offers several attractive features: CR>1 000 000:1, peak brightness=1500 nits, HDR: 10-bit mini-LED and 8-bit LCD, and thin profile.

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The production of LCD screens uses nitrogen trifluoride (NF3) as an etching fluid during the production of the thin-film components. NF3 is a potent greenhouse gas, and its relatively long half-life may make it a potentially harmful contributor to global warming. A report in Geophysical Research Letters suggested that its effects were theoretically much greater than better-known sources of greenhouse gasses like carbon dioxide. As NF3 was not in widespread use at the time, it was not made part of the Kyoto Protocol and was deemed "the missing greenhouse gas".[174] NF3 was added to the Kyoto Protocol for the second compliance period during the Doha Round.[175]

Currently, both LCDs and OLEDs are commercialized and compete with each other in almost every display segment. They are basically two different technologies (non-emissive vs. emissive), but as a display, they share quite similar perspectives in the near future. Here we will focus on three aspects: HDR, VR/AR and smart displays with versatile functions.

Some LCD panels have defective transistors, causing permanently lit or unlit pixels which are commonly referred to as stuck pixels or dead pixels respectively. Unlike integrated circuits (ICs), LCD panels with a few defective transistors are usually still usable. Manufacturers' policies for the acceptable number of defective pixels vary greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea.[150] As of 2005,[update] Samsung adheres to the less restrictive ISO 13406-2 standard.[151] Other companies have been known to tolerate as many as 11 dead pixels in their policies.[152]

The LCD panel is powered by LCD drivers that are carefully matched up with the edge of the LCD panel at the factory level. The drivers may be installed using several methods, the most common of which are COG (Chip-On-Glass) and TAB (Tape-automated bonding) These same principles apply also for smartphone screens that are much smaller than TV screens.[119][120][121] LCD panels typically use thinly-coated metallic conductive pathways on a glass substrate to form the cell circuitry to operate the panel. It is usually not possible to use soldering techniques to directly connect the panel to a separate copper-etched circuit board. Instead, interfacing is accomplished using anisotropic conductive film or, for lower densities, elastomeric connectors.

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Bistable LCDs do not require continuous refreshing. Rewriting is only required for picture information changes. In 1984 HA van Sprang and AJSM de Vaan invented an STN type display that could be operated in a bistable mode, enabling extremely high resolution images up to 4000 lines or more using only low voltages.[131] Since a pixel may be either in an on-state or in an off state at the moment new information needs to be written to that particular pixel, the addressing method of these bistable displays is rather complex, a reason why these displays did not make it to the market. That changed when in the 2010 "zero-power" (bistable) LCDs became available. Potentially, passive-matrix addressing can be used with devices if their write/erase characteristics are suitable, which was the case for ebooks which need to show still pictures only. After a page is written to the display, the display may be cut from the power while retaining readable images. This has the advantage that such ebooks may be operated for long periods of time powered by only a small battery.

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Until Gen 8, manufacturers would not agree on a single mother glass size and as a result, different manufacturers would use slightly different glass sizes for the same generation. Some manufacturers have adopted Gen 8.6 mother glass sheets which are only slightly larger than Gen 8.5, allowing for more 50- and 58-inch LCDs to be made per mother glass, specially 58-inch LCDs, in which case 6 can be produced on a Gen 8.6 mother glass vs only 3 on a Gen 8.5 mother glass, significantly reducing waste.[22] The thickness of the mother glass also increases with each generation, so larger mother glass sizes are better suited for larger displays. An LCD module (LCM) is a ready-to-use LCD with a backlight. Thus, a factory that makes LCD modules does not necessarily make LCDs, it may only assemble them into the modules. LCD glass substrates are made by companies such as AGC Inc., Corning Inc., and Nippon Electric Glass.

In the 2020s, China became the largest manufacturer of LCDs and Chinese firms had a 40% share of the global market.[76]: 126  Chinese firms that developed into world industry leaders included BOE Technology, TCL-CSOT, TIANMA, and Visionox.[76]: 126  Local governments had a significant role in this growth, including as a result of their investments in LCD manufacturers via state-owned investment companies.[76]: 126  China had previously imported significant amounts of LCDs, and the growth of its LCD industry decreased prices for other consumer products that use LCDs and led to growth in other sectors like mobile phones.[76]: 126

Power consumption is equally important as other metrics. For LCDs, power consumption consists of two parts: the backlight and driving electronics. The ratio between these two depends on the display size and resolution density. For a 55″ 4K LCD TV, the backlight occupies approximately 90% of the total power consumption. To make full use of the backlight, a dual brightness enhancement film is commonly embedded to recycle mismatched polarized light106. The total efficiency could be improved by ~60%.

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In 1972 North American Rockwell Microelectronics Corp introduced the use of DSM LCDs for calculators for marketing by Lloyds Electronics Inc, though these required an internal light source for illumination.[50] Sharp Corporation followed with DSM LCDs for pocket-sized calculators in 1973[51] and then mass-produced TN LCDs for watches in 1975.[52] Other Japanese companies soon took a leading position in the wristwatch market, like Seiko and its first 6-digit TN-LCD quartz wristwatch, and Casio's 'Casiotron'. Color LCDs based on Guest-Host interaction were invented by a team at RCA in 1968.[53] A particular type of such a color LCD was developed by Japan's Sharp Corporation in the 1970s, receiving patents for their inventions, such as a patent by Shinji Kato and Takaaki Miyazaki in May 1975,[54] and then improved by Fumiaki Funada and Masataka Matsuura in December 1975.[55] TFT LCDs similar to the prototypes developed by a Westinghouse team in 1972 were patented in 1976 by a team at Sharp consisting of Fumiaki Funada, Masataka Matsuura, and Tomio Wada,[56] then improved in 1977 by a Sharp team consisting of Kohei Kishi, Hirosaku Nonomura, Keiichiro Shimizu, and Tomio Wada.[57] However, these TFT-LCDs were not yet ready for use in products, as problems with the materials for the TFTs were not yet solved.

Segment LCDs can also have color by using Field Sequential Color (FSC LCD). This kind of displays have a high speed passive segment LCD panel with an RGB backlight. The backlight quickly changes color, making it appear white to the naked eye. The LCD panel is synchronized with the backlight. For example, to make a segment appear red, the segment is only turned ON when the backlight is red, and to make a segment appear magenta, the segment is turned ON when the backlight is blue, and it continues to be ON while the backlight becomes red, and it turns OFF when the backlight becomes green. To make a segment appear black, the segment is always turned ON. An FSC LCD divides a color image into 3 images (one Red, one Green and one Blue) and it displays them in order. Due to persistence of vision, the 3 monochromatic images appear as one color image. An FSC LCD needs an LCD panel with a refresh rate of 180 Hz, and the response time is reduced to just 5 milliseconds when compared with normal STN LCD panels which have a response time of 16 milliseconds.[133][134] FSC LCDs contain a Chip-On-Glass driver IC can also be used with a capacitive touchscreen. This technique can also be applied in displays meant to show images, as it can offer higher light transmission and thus potential for reduced power consumption in the backlight due to omission of color filters in LCDs.[135]

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This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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Currently, displays are no longer limited to traditional usages, such as TVs, pads or smartphones. Instead, they have become more diversified and are used in smart windows, smart mirrors, smart fridges, smart vending machines and so on. They have entered all aspects of our daily lives.

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In 1922, Georges Friedel described the structure and properties of liquid crystals and classified them in three types (nematics, smectics and cholesterics). In 1927, Vsevolod Frederiks devised the electrically switched light valve, called the Fréedericksz transition, the essential effect of all LCD technology. In 1936, the Marconi Wireless Telegraph company patented the first practical application of the technology, "The Liquid Crystal Light Valve". In 1962, the first major English language publication Molecular Structure and Properties of Liquid Crystals was published by Dr. George W. Gray.[31] In 1962, Richard Williams of RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what are now called "Williams domains" inside the liquid crystal.[32]

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Also worth mentioning here is ultra-high brightness. Mostly, people pay more attention to the required high CR (CR>100 000:1) of HDR but fail to notice that CR is jointly determined by the dark state and peak brightness. For example, a 12-bit Perceptual Quantizer curve is generated for a range up to 10 000 nits, which is far beyond what current displays can provide166, 167.

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In addition to the aforementioned six display metrics, other parameters are equally important. For example, high-resolution density has become a standard for all high-end display devices. Currently, LCD is taking the lead in consumer electronic products. Eight-hundred ppi or even >1000 ppi LCDs have already been demonstrated and commercialized, such as in the Sony 5.5″ 4k Smartphone Xperia Z5 Premium. The resolution of RGB OLEDs is limited by the physical dimension of the fine-pitch shadow mask. To compete with LCDs, most OLED displays use the PenTile RGB subpixel matrix scheme146. The effective resolution density of an RGB OLED mobile display is~500 ppi. In the PenTile configuration, the blue subpixel has a larger size than the green and red subpixels. Thus a lower current is needed to achieve the required brightness, which is helpful for improving the lifetime of the blue OLED. On the other hand, owing to the lower efficiency of the blue TTF OLED compared with the red and green phosphorescent ones, this results in higher power consumption. To further enhance the resolution density, multiple approaches have been developed, as will be discussed later.

Many manufacturers would replace a product even with one defective pixel. Even where such guarantees do not exist, the location of defective pixels is important. A display with only a few defective pixels may be unacceptable if the defective pixels are near each other. LCD panels also commonly have a defect known as clouding, dirty screen effect, or, less commonly, mura, which involves uneven patches of luminance on the panel. It is most visible in dark or black areas of displayed scenes.[154] As of 2010,[update] most premium branded computer LCD panel manufacturers specify their products as having zero defects.

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where Ton (Toff) represents the on-state (off-state) brightness of an LCD or OLED and A is the intensity of reflected light by the display device.

Immersive VR/AR are two emerging wearable display technologies with great potential in entertainment, education, training, design, advertisement and medical diagnostics. However, new opportunities arise along with new challenges. VR head-mounted displays require a resolution density as high as >2000 ppi to eliminate the so-called screen door effect and generate more realistic immersive experiences.

In the late 1960s, pioneering work on liquid crystals was undertaken by the UK's Royal Radar Establishment at Malvern, England. The team at RRE supported ongoing work by George William Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals, which had correct stability and temperature properties for application in LCDs.[41]

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What is lcd tftused for

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If we want to further suppress image blur to an unnoticeable level (MPRT<2 ms), decreasing the duty ratio (for LCDs, this is the on-time ratio of the backlight, called scanning backlight or blinking backlight) is mostly adopted59, 60, 61. However, the tradeoff is reduced brightness. To compensate for the decreased brightness due to the lower duty ratio, we can boost the LED backlight brightness. For OLEDs, we can increase the driving current, but the penalties are a shortened lifetime and efficiency roll-off62, 63, 64.

A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liquid crystals do not emit light directly[1] but instead use a backlight or reflector to produce images in color or monochrome.[2]

TFT LCDvs AMOLED

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Recently, ‘Liquid crystal display (LCD) vs. organic light-emitting diode (OLED) display: who wins?’ has become a topic of heated debate. In this review, we perform a systematic and comparative study of these two flat panel display technologies. First, we review recent advances in LCDs and OLEDs, including material development, device configuration and system integration. Next we analyze and compare their performances by six key display metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility. In this section, we focus on two key parameters: motion picture response time (MPRT) and ambient contrast ratio (ACR), which dramatically affect image quality in practical application scenarios. MPRT determines the image blur of a moving picture, and ACR governs the perceived image contrast under ambient lighting conditions. It is intriguing that LCD can achieve comparable or even slightly better MPRT and ACR than OLED, although its response time and contrast ratio are generally perceived to be much inferior to those of OLED. Finally, three future trends are highlighted, including high dynamic range, virtual reality/augmented reality and smart displays with versatile functions.

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As for AR applications, lightweight, low power and high brightness are mainly determined by the display components. LC on silicon can generate high brightness182, but its profile is too bulky and heavy with the implementation of a polarization beam splitter. Removing the polarization beam splitter with a front light guide would be the appropriate solution183. However, integrating RGB LEDs with this light guide remains a significant challenge. Additionally, RGB LEDs, especially green LEDs, are not efficient enough. OLEDs have thin profiles, but their peak brightness and power efficiency are still far from satisfactory, especially for such AR devices, as they are mostly used outdoors, meaning high brightness is commonly required to increase the ACR of displayed images.

In 1990, under different titles, inventors conceived electro optical effects as alternatives to twisted nematic field effect LCDs (TN- and STN- LCDs). One approach was to use interdigital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates.[68][69] To take full advantage of the properties of this In Plane Switching (IPS) technology further work was needed. After thorough analysis, details of advantageous embodiments are filed in Germany by Guenter Baur et al. and patented in various countries.[70][71] The Fraunhofer Institute ISE in Freiburg, where the inventors worked, assigns these patents to Merck KGaA, Darmstadt, a supplier of LC substances. In 1992, shortly thereafter, engineers at Hitachi work out various practical details of the IPS technology to interconnect the thin-film transistor array as a matrix and to avoid undesirable stray fields in between pixels.[72][73] The first wall-mountable LCD TV was introduced by Sharp Corporation in 1992.[74]

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LCDs have limited flexibility. A curved TV is practical but going beyond that is rather difficult with rigid and thick glass substrates139. Fortunately, this obstacle has been removed with the implementation of a thin plastic substrate140, 141, 142. In 2017, a 12.1″ rollable LCD using organic TFT, called OLCD, was demonstrated, and its radius of curvature is 60 mm143. To maintain a uniform cell gap, a polymer wall was formed within the LC layer144. Additionally, it is reported that LCDs could be foldable with a segmented backlight. This is a good choice, but until now, no demo or real device has been demonstrated. Combining two bezel-less LCDs together is another solution to enable a foldable display, but this technology is still under development145.

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It is worth mentioning that, although IQE could be as high as 100% in theory, due to the refractive index difference the emission generated inside the OLED experiences total internal reflection, which reduces the extraction efficiency. Taking a bottom emission OLED with a glass substrate (n~1.5) and an indium-tin-oxide anode (n~1.8) as an example, the final extraction efficiency is only ~20%52.

In 2007 the image quality of LCD televisions surpassed the image quality of cathode-ray-tube-based (CRT) TVs.[77] In the fourth quarter of 2007, LCD televisions surpassed CRT TVs in worldwide sales for the first time.[78] LCD TVs were projected to account 50% of the 200 million TVs to be shipped globally in 2006, according to Displaybank.[79][80]

We thank Guanjun Tan and Ruidong Zhu for helpful discussions and AFOSR for partial financial support under contract No. FA9550-14-1-0279.

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Calculated ACR as a function of different ambient light conditions for LCD and OLED smartphones. Reflectance is assumed to be 4.4% for both LCD and OLED. (a) LCD CR: 2000:1, OLED CR: infinity; (b) LCD CR: 3000:1, OLED CR: infinity. (LCD peak brightness: 600 nits; OLED peak brightness: 500 nits).

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High-resolution color displays, such as modern LCD computer monitors and televisions, use an active-matrix structure. A matrix of thin-film transistors (TFTs) is added to the electrodes in contact with the LC layer. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is selected, all of the column lines are connected to a row of pixels and voltages corresponding to the picture information are driven onto all of the column lines. The row line is then deactivated and the next row line is selected. All of the row lines are selected in sequence during a refresh operation. Active-matrix addressed displays look brighter and sharper than passive-matrix addressed displays of the same size, and generally have quicker response times, producing much better images. Sharp produces bistable reflective LCDs with a 1-bit SRAM cell per pixel that only requires small amounts of power to maintain an image.[132]

Here we focus on two types of lifetime: storage and operational. To enable a 10-year storage lifetime, according to the analysis94, the water vapor permeation rate and oxygen transmission rate for an OLED display should be <1 × 10−6 g (m2-day)−1 and 1 × 10−5 cm3 (m2-day)−1, respectively. To achieve these values, organic and/or inorganic thin films have been developed to effectively protect the OLED and lengthen its storage lifetime. Meanwhile, it is compatible to flexible substrates and favors a thinner display profile95, 96, 97.

In 2015 LG Display announced the implementation of a new technology called M+ which is the addition of white subpixel along with the regular RGB dots in their IPS panel technology.[137]

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LCDs are used in a wide range of applications, including LCD televisions, computer monitors, instrument panels, aircraft cockpit displays, and indoor and outdoor signage. Small LCD screens are common in LCD projectors and portable consumer devices such as digital cameras, watches, calculators, and mobile telephones, including smartphones. LCD screens have replaced heavy, bulky and less energy-efficient cathode-ray tube (CRT) displays in nearly all applications.

Most color LCD systems use the same technique, with color filters used to generate red, green, and blue subpixels. The LCD color filters are made with a photolithography process on large glass sheets that are later glued with other glass sheets containing a thin-film transistor (TFT) array, spacers and liquid crystal, creating several color LCDs that are then cut from one another and laminated with polarizer sheets. Red, green, blue and black colored photoresists (resists) are used to create color filters. All resists contain a finely ground powdered pigment, with particles being just 40 nanometers across. The black resist is the first to be applied; this will create a black grid (known in the industry as a black matrix) that will separate red, green and blue subpixels from one another, increasing contrast ratios and preventing light from leaking from one subpixel onto other surrounding subpixels.[6] After the black resist has been dried in an oven and exposed to UV light through a photomask, the unexposed areas are washed away, creating a black grid. Then the same process is repeated with the remaining resists. This fills the holes in the black grid with their corresponding colored resists.[7][8][9] Black matrices made in the 1980s and 1990s when most color LCD production was for laptop computers, are made of Chromium due to its high opacity, but due to environmental concerns, manufacturers shifted to black colored photoresist with carbon pigment as the black matrix material.[10][11][12] Another color-generation method used in early color PDAs and some calculators was done by varying the voltage in a Super-twisted nematic LCD, where the variable twist between tighter-spaced plates causes a varying double refraction birefringence, thus changing the hue.[13] They were typically restricted to 3 colors per pixel: orange, green, and blue.[14]

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A color filter array is another effective approach to enhance the color gamut of an OLED. For example, in 2017, AUO demonstrated a 5-inch top-emission OLED panel with 95% Rec. 2020. In this design, so-called symmetric panel stacking with a color filter is employed to generate purer RGB primary colors92. Similarly, SEL developed a tandem white top-emitting OLED with color filters to achieve a high color gamut (96% Rec. 2020) and high resolution density (664 pixels per inch (ppi) simultaneously93.

The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure (prism sheet) to gain the light into the desired viewer directions and reflective polarizing films that recycle the polarized light that was formerly absorbed by the first polarizer of the LCD (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman),[111] generally achieved using so called DBEF films manufactured and supplied by 3M.[112] Improved versions of the prism sheet have a wavy rather than a prismatic structure, and introduce waves laterally into the structure of the sheet while also varying the height of the waves, directing even more light towards the screen and reducing aliasing or moiré between the structure of the prism sheet and the subpixels of the LCD. A wavy structure is easier to mass-produce than a prismatic one using conventional diamond machine tools, which are used to make the rollers used to imprint the wavy structure into plastic sheets, thus producing prism sheets.[113] A diffuser sheet is placed on both sides of the prism sheet to distribute the light of the backlight uniformly, while a mirror is placed behind the light guide plate to direct all light forwards. The prism sheet with its diffuser sheets are placed on top of the light guide plate.[114][97] The DBEF polarizers consist of a large stack of uniaxial oriented birefringent films that reflect the former absorbed polarization mode of the light.[115]

Displays having a passive-matrix structure use super-twisted nematic STN (invented by Brown Boveri Research Center, Baden, Switzerland, in 1983; scientific details were published[125]) or double-layer STN (DSTN) technology (the latter of which addresses a color-shifting problem with the former), and color-STN (CSTN), in which color is added by using an internal color filter. STN LCDs have been optimized for passive-matrix addressing. They exhibit a sharper threshold of the contrast-vs-voltage characteristic than the original TN LCDs. This is important, because pixels are subjected to partial voltages even while not selected. Crosstalk between activated and non-activated pixels has to be handled properly by keeping the RMS voltage of non-activated pixels below the threshold voltage as discovered by Peter J. Wild in 1972,[126] while activated pixels are subjected to voltages above threshold (the voltages according to the "Alt & Pleshko" drive scheme).[127] Driving such STN displays according to the Alt & Pleshko drive scheme require very high line addressing voltages. Welzen and de Vaan invented an alternative drive scheme (a non "Alt & Pleshko" drive scheme) requiring much lower voltages, such that the STN display could be driven using low voltage CMOS technologies.[60] White-on-blue LCDs are STN and can use a blue polarizer, or birefringence which gives them their distinctive appearance.[128][129][130]

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As mentioned earlier, TFT LCDs are a fairly mature technology. They can be operated for >10 years without noticeable performance degradation. However, OLEDs are more sensitive to moisture and oxygen than LCDs. Thus their lifetime, especially for blue OLEDs, is still an issue. For mobile displays, this is not a critical issue because the expected usage of a smartphone is approximately 2–3 years. However, for large TVs, a lifetime of >30 000 h (>10 years) has become the normal expectation for consumers.

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The zenithal bistable device (ZBD), developed by Qinetiq (formerly DERA), can retain an image without power. The crystals may exist in one of two stable orientations ("black" and "white") and power is only required to change the image. ZBD Displays is a spin-off company from QinetiQ who manufactured both grayscale and color ZBD devices. Kent Displays has also developed a "no-power" display that uses polymer stabilized cholesteric liquid crystal (ChLCD). In 2009 Kent demonstrated the use of a ChLCD to cover the entire surface of a mobile phone, allowing it to change colors, and keep that color even when power is removed.[155]

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TFTdisplay vsLCD

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TFT LCDvs IPS

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Most of the new M+ technology was employed on 4K TV sets which led to a controversy after tests showed that the addition of a white sub pixel replacing the traditional RGB structure had also been accompanied by a reduction in resolution by around 25%. This meant that a "4K" M+ TV would not display the full UHD TV standard. The media and internet users called them "RGBW" TVs because of the white sub pixel. Although LG Display has developed this technology for use in notebook display, outdoor and smartphones, it became more popular in the TV market because of the announced "4K UHD" resolution but still being incapable of achieving true UHD resolution defined by the CTA as 3840x2160 active pixels with 8-bit color. This negatively impacted the rendering of text, making it a bit fuzzier, which was especially noticeable when a TV is used as a PC monitor.[138][139][140][141]

In 1964, George H. Heilmeier, who was working at the RCA laboratories on the effect discovered by Richard Williams, achieved the switching of colors by field-induced realignment of dichroic dyes in a homeotropically oriented liquid crystal. Practical problems with this new electro-optical effect made Heilmeier continue to work on scattering effects in liquid crystals and finally the achievement of the first operational liquid-crystal display based on what he called the dynamic scattering mode (DSM). Application of a voltage to a DSM display switches the initially clear transparent liquid crystal layer into a milky turbid state. DSM displays could be operated in transmissive and in reflective mode but they required a considerable current to flow for their operation.[35][36][37][38] George H. Heilmeier was inducted in the National Inventors Hall of Fame[39] and credited with the invention of LCDs. Heilmeier's work is an IEEE Milestone.[40]

Recently, a new LED technology, called the Vivid Color LED, was demonstrated86. Its FWHM is only 10 nm (Figure 9d), which leads to an unprecedented color gamut (~98% Rec. 2020) together with specially designed color filters. Such a color gamut is comparable to that of laser-lit displays but without laser speckles. Moreover, the Vivid Color LED is heavy-metal free and shows good thermal stability. If the efficiency and cost can be further improved, it would be a perfect candidate for an LCD backlight.

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, often made of indium tin oxide (ITO) and two polarizing filters (parallel and perpendicular polarizers), the axes of transmission of which are (in most of the cases) perpendicular to each other. Without the liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. Before an electric field is applied, the orientation of the liquid-crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic (TN) device, the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This induces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.

The 90° TN mode was first published in 1971 by Schadt and Helfrich13. In the voltage-off state, the LC director twists 90° continually from the top to the bottom substrates (Figure 2a), introducing a so-called polarization rotation effect. As the voltage exceeds a threshold (Vth), the LC directors start to unwind and the polarization rotation effect gradually diminishes, leading to decreased transmittance. This TN mode has a high transmittance and low operation voltage (~5 Vrms), but its viewing angle is somewhat limited22. To improve the viewing angle and extend its applications to desktop computers and TVs, some specially designed compensation films, such as discotic film or Fuji film, are commonly used23, 24. Recently, Sharp developed a special micro-tube film to further widen the viewing angle and ambient contrast ratio (ACR) for TN LCDs25.

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Displays for a small number of individual digits or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment.[15] In contrast, full alphanumeric or variable graphics displays are usually implemented with pixels arranged as a matrix consisting of electrically connected rows on one side of the LC layer and columns on the other side, which makes it possible to address each pixel at the intersections. The general method of matrix addressing consists of sequentially addressing one side of the matrix, for example by selecting the rows one-by-one and applying the picture information on the other side at the columns row-by-row. For details on the various matrix addressing schemes see passive-matrix and active-matrix addressed LCDs.

A QD-enhanced backlight (e.g., quantum dot enhancement film, QDEF) offers another option for a wide color gamut20, 80, 81. QDs exhibit a much narrower bandwidth (FWHM~20–30 nm) (Figure 9c), so that high purity RGB colors can be realized and a color gamut of ~90% Rec. 2020 can be achieved. One safety concern is that some high-performance QDs contain the heavy metal Cd. To be compatible with the restriction of hazardous substances, the maximum cadmium content should be under 100 ppm in any consumer electronic product82. Some heavy-metal-free QDs, such as InP, have been developed and used in commercial products83, 84, 85.

High CR is a critical requirement for achieving supreme image quality. OLEDs are emissive, so, in theory, their CR could approach infinity to one. However, this is true only under dark ambient conditions. In most cases, ambient light is inevitable. Therefore, for practical applications, a more meaningful parameter, called the ACR, should be considered65, 66, 67, 68:

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In this period, Taiwanese, Japanese, and Korean manufacturers were the dominant firms in LCD manufacturing.[76]: 126  From 2001 to 2006, Samsung and five other major companies held 53 meetings in Taiwan and South Korea to fix prices in the LCD industry.[76]: 127  These six companies were fined 1.3 billion dollars by the United States, 650 million Euro by the European Union, and 350 million RMB by China's National Development and Reform Commission.[76]: 127

The last finding is somehow counter to the intuition that a LCD should have a more severe motion picture image blur, as its response time is approximately 1000 × slower than that of an OLED (ms vs. μs). To validate this prediction, Chen et al.58 performed an experiment using an ultra-low viscosity LC mixture in a commercial VA test cell. The measured average gray-to-gray response time is 1.29 ms by applying a commonly used overdrive and undershoot voltage method. The corresponding average MPRT at 120 fps is 6.88 ms, while that of an OLED is 6.66 ms. These two results are indeed comparable. If the frame rate is doubled to 240 fps, both LCDs and OLEDs show a much faster but still similar MPRT values (3.71 vs. 3.34 ms). Thus the above finding is confirmed experimentally.

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Schematic diagram of an LCD. BEF, brightness enhancement film; BLU, backlight unit; DBEF, dual brightness enhancement film; LGP, light guide plate.

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