Doped Organic Light-emitting Diodes Research Articles

Copper(I) TADF exciplexes via Metal-Perturbed Through-Space charge transfer for efficient OLEDs

Organo-copper(I) emitters are promising cost-effective candidates as triplet-harvesting dopants in organic light-emitting diodes (OLEDs). To date, the mainstream design of Cu(I) emitters depends on ligand engineering to modify intramolecular charge transfer and thus modulate the related optoelectronic properties. However, little is known on luminescent Cu(I) systems based on intermolecular charge transfer. For the first time, the proof-of-concept Cu(I) exciplexes were developed employing a triazine-containing molecule DMIC-TRZ as an acceptor and several Cu(I)-based carbene-metal-amide (CMA) complexes as donors. The formation of these exciplexes is strongly associated with d-orbital participation of Cu atom on the highest occupied molecular orbital of CMA complexes to match with the acceptor DMIC-TRZ. These Cu(I) exciplexes not only displayed donor-dependent emission colors spanning from sky blue to red but also exhibited distinct thermally activated delayed fluorescence (TADF) via copper(I)-perturbed through-space charge transfer (TSCT). The OLEDs adopting the Cu(I) exciplexes as emitters delivered good external quantum efficiency (EQE) of up to 10.9%. Furthermore, the use of these Cu(I) exciplexes as hosts for multi-resonance TADF emitters delivered narrowband electroluminescence with high EQEs of up to 24.9%, superior to the reference OLEDs based on the common host.

Efficient deep-red Aggregate-Induced emission material and “Hot-exciton” electroluminescence

Organic deep-red fluorescent materials have a wide range of applications in organic light-emitting diodes (OLEDs), biological imaging, night-vision equipment, and other fields. Here, we designed and synthesized a new deep-red emissive donor–acceptor (D-A) compound TPANZPPICN, whose non-doped OLED achieves stable pure deep-red electroluminescence (EL) at 692 nm with a maximum external quantum efficiency (EQE) of 2.67 % in non-doped OLED and a maximum EQE of 7.96 % at 660 nm in doped OLED. Magneto-electroluminescence (MEL) measurements reveal a negative response in the doped OLED, which is a significant character of reversed intersystem crossing (RISC) on high-lying excited states. Both theoretical calculations and experimental results confirm that the hot-exciton mechanism is responsible for the high efficiency EL of doped OLED, which proves to be a novel approach to realize the efficient deep-red organic fluorescent OLEDs.

Hybridization of short-range and long-range charge transfer excited states in multiple resonance emitter

Multiple resonance (MR) thermally activated delayed fluorescence emitters have been actively studied as pure blue dopants for organic light-emitting diodes (OLEDs) because of excellent color purity and high efficiency. However, the reported MR emitter, 2,5,13,16-tetra-tert-butylindolo[3,2,1-jk]indolo[1′,2′,3′:1,7]indolo[2,3-b]carbazole (tDIDCz) based on bis-fused indolocarbazole framework could not demonstrate efficient triplet-to-singlet spin crossover. In this work, we report two isomeric MR emitters designed to promote triplet exciton harvesting by reconstructing the electronic structure of tDIDCz. To manage excited states, strong electron donors were introduced at the 2,5-/1,6-position of tDIDCz. As a result, 2,5-positions managed tDIDCz shows long-range charge transfer characteristics while preserving the MR nature. Quantum chemical calculation demonstrates direct spin-orbit coupling by long-range charge transfer and spin-vibronic coupling assisted reverse intersystem crossing by short-range charge transfer simultaneously contribute to triplet-to-singlet spin crossover. Consequently, high performance blue OLED recorded a high external quantum efficiency of 30.8% at a color coordinate of (0.13, 0.13).

Enhanced triplet-triplet fusion for high efficiency and long lifetime of multiresonant pure blue organic light emitting diodes

Multiresonant (MR) narrowband emitters became extensive attention as a blue fluorescent dopant for organic light-emitting diodes (OLEDs) due to their high color purity and large photoluminescence quantum yields (PLQY), but they show poor operational lifetime. Herein, we present a double emissive layer (DEML) architecture to enhance the efficiency and lifetime of pure blue fluorescent OLEDs for MR type emitters. Mainly the DEML are divided into recombination zone and triplet–triplet fusion (TTF) zone based on different triplet energy hosts. Notably, we achieved a tremendous TTF ratio of 32.4% for MR-type dopant, which is close to the theoretical maximum of 37.5%. Furthermore, fabricated fluorescent devices based on DEML structure manifested tremendous maximum external quantum efficiency (EQEmax) of nearly 11% and revealed a longer lifetime (LT95) of 79 h at 1000 cd/m2 due to efficient triplet harvesting, which is almost double compared to the single host device. We believe that our findings can pave the way for enhancement in EQE and lifetime for blue OLEDs.

Improving Electroluminescence Efficiency by Linear Polar Host Capable of Promoting Horizontal Dipole Orientation for Dopant

In doped organic light-emitting diodes (OLEDs), the host materials play an important role in emitting layers. Most studies about host materials mainly focus on their energy levels and carrier transport behaviors, while less attention is paid to their influence on the dipole orientation of dopants, which closely associate with the light out-coupling efficiency (ηout ) of the device. Herein, a linear polar host material (l-CzTRZ) consisting of carbazole donor, triazine acceptor, and the conjugated para-terphenyl skeleton is developed and its crystal and electronic structures, thermal and electrochemical stabilities, optical property, and carrier transport ability are investigated. l-CzTRZ prefers ordered horizontal orientation and favors electron transport in neat film. More importantly, it can promote horizontal dipole orientation for the dopants via dipole-dipole interaction, furnishing an excellent horizontal dipole ratio of 91.5% and thus a high ηout of 43% for the phosphorescent dopant (PO-01-TB). Consequently, the OLED with l-CzTRZ host and PO-01-TB dopant attains state-of-the-art electroluminescence efficiencies of 135.5cd A-1 , 135.7 lm W-1 and 41.3%, with a small roll-off of 9.7% at 5000cdm-2 luminance. The presented significant impact of the host on the dipole orientation of the dopant shall enlighten the design of host materials to improve OLED performance.

Face-to-face order-packed mode promotes thermally activated delayed fluorescence to achieve stronger aggregation-induced emission

Two novel aggregation-induced delayed fluorescence materials (AIDF) FCP-BP-PXZ [9- (4-Fluorophenyl) -9H-carbazole-3-yl] [4- (10H-phenoxazine-10-yl) phenyl] methane and FCP-BP-PTZ [9- (4-Fluorophenyl) -9H-carbazole-3-yl] [4- (10H-penzothiazin-10-yl) phenyl] methane were synthesized. Experiments and molecular dynamics (MD) simulations revealed that FCP-BP-PXZ exhibits orderly face-to-face arrangement stacking mode, which inhibits non-radiation inactivation channel and reduces energy loss by restricting larger vibration and rotation of the molecule due to abundant intermolecular hydrogen bonds and strong intermolecular π-π interactions. FCP-BP-PTZ 's performance was hampered by erratic relaxation aggregation. The maximal external quantum efficiency (EQE max ) of non-doped and doped organic light-emitting diodes (OLEDs) constructed on FCP-BP-PXZ was 11.2% and 18.2%, respectively. Furthermore, at a brightness of 1000 cd m −2 , non-doped and doped devices had a low turn-on voltage of 3.0–3.5 V, with 2.0% and 3.3% efficiency roll-off, owing to the microsecond-scale delayed lifetime. The FCP-BP-PXZ -based non-doped device, in particular, achieved a brightness of 62,390 cd m −2 , which was crucial in non-doped yellow OLEDs.

Low efficiency roll-off thermally activated delayed fluorescence emitters for non-doped OLEDs: Substitution effect of thioether and sulfone groups

The non-doped organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) materials are attracting increasing attentions due to the excellent performance and simple fabrication. We report an effective design strategy of TADF emitters to improve the non-doped performance by adjusting the valence state of the S atom in TADF molecules and utilizing the steric hindrance effect. Two novel TADF materials PT-BZ-DMAC and PS-BZ-DMAC were designed and synthesized with benzophenone acceptor and acridine donor. In particular, the thioether or sulfone group was attached to benzophenone. Remarkably, the bluish-green TADF-OLED with non-doped PT-BZ-DMAC turned on at 2.5 V and realized a maximum external quantum efficiency (EQE) of 17.34%, which was comparable with its doped OLED (17.71%) but showed much slower roll-off. At 100 and 1000 cd m−2, the non-doped PT-BZ-DMAC device still maintained acceptable efficiencies at 14.65% and 12.59%. In contrast, sulfone-modified PS-BZ-DMAC exhibited good efficiency of 20.55% only in doped OLED. The single crystal analysis and DFT calculation revealed that the phenyl thioether unit in PT-BZ-DMAC hardly contributes to the LUMO or the electronic transitions, instead determines the highly twisted geometry and acts as the barrier group, finally improving the performance of PT-BZ-DMAC in neat film device.

Ultra‐Deep‐Blue Aggregation‐Induced Delayed Fluorescence Emitters: Achieving Nearly 16% EQE in Solution‐Processed Nondoped and Doped OLEDs with CIEy < 0.1

AbstractUltra‐deep‐blue aggregation‐induced delayed fluorescence (AIDF) emitters (TB‐tCz and TB‐tPCz) bearing organoboron‐based cores as acceptors and 3,6‐substituted carbazoles as donors are presented. The thermally activated delayed fluorescence (TADF) properties of the two emitters are confirmed by theoretical calculations and time‐resolved photoluminescence experiments. TB‐tCz and TB‐tPCz exhibit fast reverse intersystem crossing rate constants owing to efficient spin–orbit coupling between the singlet and triplet states. When applied in solution‐processed organic light‐emitting diodes (OLEDs), the TB‐tCz‐ and TB‐tPCz‐based nondoped devices exhibit ultra‐deep‐blue emissions of 416–428 nm and high color purity owing to their narrow bandwidths of 42.2–44.4 nm, corresponding to the Commission International de l´Eclairage color coordinates of (x = 0.16–0.17, y = 0.05–0.06). They show a maximum external quantum efficiency (EQEmax) of 8.21% and 15.8%, respectively, exhibiting an unprecedented high performance in solution‐processed deep‐blue TADF‐OLEDs. Furthermore, both emitters exhibit excellent device performances (EQEmax = 14.1–15.9%) and color purity in solution‐processed doped OLEDs. The current study provides an AIDF emitter design strategy to implement high‐efficiency deep‐blue OLEDs in the future.

Circularly Polarized Thermally Activated Delayed Fluorescence Emitters in Through-Space Charge Transfer on Asymmetric Spiro Skeletons.

This work describes a strategy to produce circularly polarized thermally activated delayed fluorescence (CP-TADF). A set of two structurally similar organic emitters SFST and SFOT are constructed, whose spiro architectures containing asymmetric donors result in chirality. Upon grafting within the spiro frameworks, the donor and acceptor are fixed proximally in a face-to-face manner. This orientation allows intramolecular through-space charge transfer (TSCT) to occur in both emitters, leading to TADF properties. The donor units in SFST and SFOT have a sulfur and oxygen atom, respectively; such a subtle difference has great impacts on their photophysical, chiroptical, and electroluminescence (EL) properties. SFOT exhibits greatly enhanced EL performance in doped organic light-emitting diodes, with external quantum efficiency (EQE) up to 23.1%, owing to the concurrent manipulation of highly photoluminescent quantum efficiency (PLQY, ∼90%) and high exciton utilization. As a comparison, the relatively larger sulfur atom in SFST introduces heavy atom effects and leads to distortion of the molecular backbone that lengthens the donor-acceptor distance. SFST thus has lower PLQY and faster nonradiative decay rate. The collective consequence is that the EQE value of SFST, i.e., 12.5%, is much lower than that of SFOT. The chirality of these two spiro emitters results in circularly polarized luminescence. Because SFST has a more distorted molecular architecture than SFOT, the luminescence dissymmetry factor (|glum|) of circularly polarized luminescence of one enantiomer of the former, namely, either (S)-SFST or (R)-SFST, is almost twice that of (S)-SFOT/(R)-SFOT. Moreover, the CP organic light-emitting diodes (CP-OLEDs) show obvious circularly polarized electroluminescence (CPEL) signals with gEL of 1.30 × 10-3 and 1.0 × 10-3 for (S)-SFST and (S)-SFOT, respectively.

High-Performance Solution-Processed Red Thermally Activated Delayed Fluorescence OLEDs Employing Aggregation-Induced Emission-Active Triazatruxene-Based Emitters

Two novel red thermally activated delayed fluorescence (TADF) emitters (TAT-DBPZ and TAT-FDBPZ) were developed by incorporating triazatruxene (TAT) as the electron donor (D) and dibenzo[a,c]phenazine (DBPZ) or fluorine-substituted dibenzo[a,c]phenazine (FDBPZ) as the electron acceptor (A). Both compounds showed aggregation-induced emission (AIE) behaviors and bright red emission in neat films. Benefited from the rigid and large planar conjugated structures of TAT and DBPZ, TAT-DBPZ and TAT-FDBPZ realized high photoluminescence quantum yields (PLQYs) in solid states. Meanwhile, the large steric hindrance between TAT and DBPZ segments produced small singlet-triplet energy splitting (EST), leading to short delayed fluorescence lifetimes and high reverse intersystem crossing (RISC) rate (106 s-1) for both compounds. The solution-processable doped organic light-emitting diodes (OLEDs) based on TAT-DBPZ achieved a high external quantum efficiency (EQE) of 15.4% with a red emission peak at 604 nm, which was one of the highly efficient solution-processable red TADF OLEDs. TAT-FDBPZ based doped devices also showed a red emission peak at 611 nm with a maximum EQE of 9.2% and low efficiency roll-off ratios of 1.0% at 100 cd m-2 and 19% at 1000 cd m-2. Furthermore, their solution-processable non-doped devices displayed EQEs of 5.6% and 2.9% with the red-shifted emission peaks at 626 nm and 641 nm, respectively. These results indicate the huge potential of utilization of triazatruxene as donor unit to achieve highly efficient and low efficiency roll-off solution-processable red TADF OLEDs.

Towards blue AIE/AIEE: Synthesis and Applications in OLEDs of Tetra-/Triphenylethenyl Substituted 9,9-Dimethylacridine Derivatives.

Aiming to design blue fluorescent emitters with high photoluminescence quantum yields in solid-state, nitrogen-containing heteroaromatic 9,9-dimethylacridine was refined by tetraphenylethene and triphenylethene. Six tetra-/triphenylethene-substituted 9,9-dimethylacridines were synthesized by the Buchwald-Hartwig method with relatively high yields. Showing effects of substitution patterns, all emitters demonstrated high fluorescence quantum yields of 26–53% in non-doped films and 52–88% in doped films due to the aggregation induced/enhanced emission (AIE/AIEE) phenomena. In solid-state, the emitters emitted blue (451–481 nm) without doping and deep-blue (438–445 nm) with doping while greenish-yellow emission was detected for two compounds with additionally attached cyano-groups. The ionization potentials of the derivatives were found to be in the relatively wide range of 5.43–5.81 eV since cyano-groups were used in their design. Possible applications of the emitters were demonstrated in non-doped and doped organic light-emitting diodes with up to 2.3 % external quantum efficiencies for simple fluorescent devices. In the best case, deep-blue electroluminescence with chromaticity coordinates of (0.16, 0.10) was close to blue color standard (0.14, 0.08) of the National Television System Committee.

Cyclometalated Ir(iii) complexes towards blue-emissive dopant for organic light-emitting diodes: fundamentals of photophysics and designing strategies

The fundamental photophysics of cyclometalated Ir(iii) complexes and surveys design strategies for efficient blue phosphorescent Ir(iii) complexes are summarised.

Synthesis of Linear and V-Shaped Carbazolyl-Substituted Pyridine-3,5-dicarbonitriles Exhibiting Efficient Bipolar Charge Transport and E-Type Fluorescence.

With the aim of developing all-organic bipolar semiconductors with high charge mobility and efficient E-type fluorescence (so-called TADF) as environmentally friendly light-emitting materials for optoelectronic applications, four noble metals-free dyes with linear and V-shapes were designed using accepting pyridine-3,5-dicarbonitrile and donating carbazole units. By exploiting a donor-acceptor design strategy and using moieties with different donating and accepting abilities, TADF emitters with a wide variety of molecular weights were synthesized to achieve the optimum combination of charge-transporting and fluorescent properties in one TADF molecule. Depending on molecule structures, different TADF emitters capable of emitting in the range from 453 to 550 nm with photoluminescence quantum yields up to 98 % for the solutions in oxygen-free toluene were obtained. All compounds showed bipolar charge-transport. Hole mobility of 2.8×10-3 cm2 /Vs at 7×105 V cm-1 was observed for the compound containing two di-tert-butyl-substituted carbazole moieties. The compounds were tested in both non-doped and doped organic light-emitting diodes using different hosts. It was shown that the developed TADF emitters are suitable for different color devices with electroluminescence ranging from blue to yellow and with brightness, maximum current and external quantum efficiencies exceeding 10 000 cd m-2 , 15 cd/A, and 7 %, respectively.

Synthesis of 1,3-Azaphospholes with Pyrrolo[1,2- a]quinoline Skeleton and Their Optical Applications.

A facile synthesis of 1,3-azaphospholes with a pyrrolo[1,2- a]quinoline skeleton has been described. These new annulated 1,3-azaphospholes exhibit good photoelectric performance and can be used as the emitting dopant in organic light-emitting diodes (OLEDs) and dye for bioimaging.

A Novel Benzo[d,e]Chromene for Organic Light Emitting Diodes (OLEDs)

Organic light emitting diodes (OLEDs) have been known for the next generation of display technology. In this work, we synthesized four benzo[d,e]chromene derivatives (BS01-BS04) varying the position of fluorine atom for OLED application. The compounds were characterized by 1H and 13C NMR, FTIR and mass spectroscopy. Their photoluminescence properties were studied which showed the thermally activated delayed fluorescence (TADF) character from intramolecular charged transfer (ICT) transition. The compounds were used as a dopant for OLEDs in the structure of ITO/NPB/BS01-BS04/Bphen/LiF/Al. The BS02 device exhibited green colour with the current efficiency at 1.28 cd/A and the power efficiency at 0.47 Im/W.

Doping chloro boron subnaphthalocyanines and chloro boron subphthalocyanine in simple OLED architectures yields warm white incandescent-like emissions

We have incorporated chloro boron subphthalocyanine (Cl-BsubPc) and chloro boron subnapthalocyanines (Cl-ClnBsubNcs) into organic light emitting diodes (OLEDs) that enabled an overall warm white emission with CIE coordinates close to that of a 60 W incandescent lightbulb. More specifically, we have shown that Cl-BsubPc and Cl-ClnBsubNcs can be used as dopant emitters in a simple host-dopant architecture, and we have compared the use of NPB and Alq3 as potential hosts for these materials. When doped into Alq3, Cl-BsubPc shows a strong orange emission, and Cl-ClnBsubNcs shows a moderately strong red emission. We have further demonstrated that Cl-BsubPc and Cl-ClnBsubNcs can be co-doped into the same layer giving combined orange and red emission peaks. A “cascade” energy transfer mechanism of sequential absorption and re-emission is proposed. Device performance characteristics such as luminance, current efficiency, photoluminescence efficiency, and external quantum efficiency are tabulated. Additionally, in view of ongoing research into white emitting OLEDs for indoor lighting purposes, the Colour Rendering Index (CRI), R9 values, and CIE co-ordinates for these devices are also discussed. We conclude from this study that the BsubNc chromophore has potential application as a red dopant in OLEDs including for indoor lighting. Additionally, given the scope for axial and peripheral derivatization of the BsubNc motif, we believe that this chromophore has many unexplored molecular design handles that will affect its ultimate performance and application in OLEDs and other opto-electronic devices.

AIEE-active blue-emitting molecules derived from methoxyl-decorated triarylcyclopentadienes: Synthesis, crystal structures, photophysical and electroluminescence properties

Five highly efficient blue-emitting triarylcyclopentadiene derivatives 1–5 were designed and synthesized by introducing phenyl, methoxyphenyl, methoxybiphenyl and methoxynaphthyl groups to cyclopentadiene backbone, respectively. These compounds possess good thermal stability with decomposition temperatures of 264–340 °C and exhibit intense blue fluorescence with maximum emission peaked at 457–470 nm. All compounds emit weak fluorescence in solution, but they become strong emitters in the aggregated state indicating typical aggregation-induced emission enhancement (AIEE) properties. AIEE behaviour was further confirmed by fluorescent changes depended on temperature and solution viscosity as well as time-resolved fluorescence lifetime measurements. Unexpected substituent effect on aggregation structures and fluorescent properties of 1–5 was also observed. Single-crystal structure analysis revealed that highly twisted conformations and bulky substituents on cyclopentadiene core could dramatically suppress the intermolecular π-π interactions leading to intense blue emission of these compounds in aggregates. Furthermore, the non-doped and doped organic light-emitting diodes (OLEDs) using compounds 2 and 5 as the emitting layers have been fabricated, respectively. A non-doped OLED with compound 5 displays good electroluminescent performance with a light-blue emission and a maximum luminance of 3886 cd/m2.

Photophysical and Electroluminescent Properties of PtAg2 Acetylide Complexes Supported with meso- and rac-Tetraphosphine.

1,2-Bis[[(diphenylphosphino)methyl](phenyl)phosphino]ethane (dpmppe) was prepared as a new tetraphosphine, and the corresponding rac and meso stereoisomers were successfully separated in view of their solubility difference in acetone. The substitution of PPh3 into Pt(PPh3)2(C≡CR)2 (R = aryl) with rac- or meso-dpmppe gives Pt(rac-dpmppe)(C≡CR)2 or Pt(meso-dpmppe)(C≡CR)2, respectively. Using Pt(rac-dpmppe)(C≡CR)2 or Pt(meso-dpmppe)(C≡CR)2 as a precursor, PtAg2 heterotrinuclear cluster complexes were synthesized and characterized by X-ray crystallography. Depending on the conformations of tetraphosphine, the structures of PtAg2 complexes supported with rac- and meso-dpmppe are quite different. The higher molecular rigidity of rac-dpmppe-supported PtAg2 complexes results in stronger phosphorescent emission than that of PtAg2 species with meso-dpmppe. The high phosphorescent quantum yields (as high as 90.5%) in doping films warrant these PtAg2 complexes as excellent phosphorescent dopants in organic light-emitting diodes (OLEDs). The peak current and external quantum efficiencies in solution-processed OLEDs are 61.0 cd A-1 and 18.1%, respectively. Electroluminescence was elaborately modulated by modifying the substituent in aromatic acetylide and the conformations in tetraphosphine so as to achieve cyan, green, green-yellow, yellow, and orange-red emission.

Engineering the Interconnecting Position of Star-Shaped Donor-π-Acceptor Molecules Based on Triazine, Spirofluorene, and Triphenylamine Moieties for Color Tuning from Deep Blue to Green.

Pi-conjugated organic molecules featuring the donor-bridge-acceptor (D-π-A) structure have been widely used in semiconducting materials owing to their rigid structure, good thermal stability, excellent charge transfer, and high emission efficiency. To investigate the effect of the D-π-A molecular structure on the photophysical properties, in this contribution, three star-shaped D-π-A isomers based on the 2,4,6-triphenyl-1,3,5-triazine, spirofluorene, and triphenylamine moieties, that is, p-TFTPA, mp-TFTPA, and m-TFTPA, were synthesized by elaborately engineering the interconnecting position in the building-block units. The optophysical properties of these compounds were systematically explored by experiments and theory calculations. Definitively, changing the interconnecting position in these molecules played a significant role in the degree of π conjugation, which resulted in tunable emission colors from deep blue to green. Moreover, these isomers were employed as emissive dopants in organic light-emitting diodes. The highest external quantum efficiency of 2.3 % and current efficiency of 6.2 cd A(-1) were achieved by using the p-TFTPA based device. This research demonstrates a feasible way to realize blue emitters by engineering D-π-A conjugation.

Review of organic light-emitting diodes with thermally activated delayed fluorescence emitters for energy-efficient sustainable light sources and displays

Thermally activated delayed fluorescence (TADF) is an emerging hot topic. Even though this photophysical mechanism itself has been described more than 50 years ago and optoelectronic devices with organic matter have been studied, improved, and even commercialized for decades now, the realization of the potential of TADF organic light-emitting diodes (OLEDs) happened only recently. TADF has been proven to be an attractive and very efficient alternative for phosphorescent materials, such as dopants in OLEDs, light-emitting electrochemical cells as well as potent emitters for chemiluminescence. In this review, the TADF concept is introduced in terms that are also understandable for nonchemists. The basic concepts behind this mechanism as well as state-of-the-art examples are discussed. In addition, the future economic impact, especially for the lighting and display market, is addressed here. We conclude that TADF materials are especially helpful to realize efficient, durable deep blue and white displays.