Facile Photo‐Crosslinking of Azide‐Containing Hole‐Transporting Polymers for Highly Efficient,Solution‐Processed,Multilayer Organic Light Emitting Devices

A novel framework of azide containing photo‐crosslinkable, conducting copolymer, that is, poly(azido‐styrene)‐random‐poly(triphenylamine) (X‐PTPA), is reported as a hole‐transporting material for efficient solution‐processed, multi‐layer, organic light emitting diodes (OLEDs). A facile and energy‐efficient crosslinking process is demonstrated with UV irradiation (254 nm, 2 mW/cm²) at a short exposure time (5 min). By careful design of X‐PTPA, in which 5 mol% of the photo‐crosslinkable poly(azido‐styrene) is copolymerized with hole‐transporting poly(triphenylamine) (X‐PTPA‐5), the adverse effect of the crosslinking of azide moieties is prevented to maximize the performances of X‐PTPA‐5. Since the photo‐crosslinking chemistry of azide molecules does not involve any photo‐initiators, superior hole‐transporting ability is achieved, producing efficient devices. To evaluate the performances of X‐PTPA‐5 as a hole‐transporting/electron‐blocking layer, Ir(ppy)₃‐based, solution‐processable OLEDs are fabricated. The results show high EQE (11.8%), luminous efficiency (43.7 cd/A), and power efficiency (10.4 lm/W), which represent about twofold enhancement over the control device without X‐PTPA‐5 film. Furthermore, micro‐patterned OLEDs with the photo‐crosslinkable X‐PTPA‐5 can be fabricated through standard photolithography. The versatility of this approach is also demonstrated by introducing the same azide moiety into other hole‐transporting materials such as poly(carbazole) (X‐PBC).     

Solution‐Processed Thermally Activated Delayed Fluorescent OLED with High EQE as 31% Using High Triplet Energy Crosslinkable Hole Transport Materials

Solution‐processed organic light‐emitting diodes (OLEDs) with thermally activated delayed fluorescent (TADF) material as emitter have attracted much attention because of their low cost and high performance. However, exciton quench at the interface between the hole injection layer, poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and emitting layer (EML) in devices can lead to low device performance. Here, a novel high triplet energy (2.89 eV) and crosslinkable hole‐transporting material grafted with oxetane groups, N,N‐bis(4‐(6‐((3‐ethyloxetan‐3‐yl)methoxy)hexyloxy)phenyl)‐3,5‐di(9H‐carbazol‐9‐yl)benzenamine (Oxe‐DCDPA)), as crosslinked hole transport layer (HTL) into the interface of PEDOT:PSS layer and EML is proposed for prevention of exciton quenching, and among the reported devices with single HTL in solution‐processed TADF‐OLED, the highest external quantum efficiency (EQE)/luminous efficiency (η_L) of 26.1%/94.8 cd A^?1 and 24.0%/74.0 cd A^?1 are achieved for green emission (DACT‐II as emitter) and bluish‐green emission (DMAC‐TRZ as emitter), respectively. Further improvement, using double HTLs, composed of N,N′‐bis(4‐(6‐((3‐ethyloxetan‐3‐yl)methoxy))‐hexylphenyl)‐N,N′‐diphenyl‐4,4′‐diamine with high hole mobility and Oxe‐DCDPA with high triplet energy, leads to the highest EQE/η_L of 30.8%/111.9 cd A^?1 and 27.2%/83.8 cd A^?1 for green emission and bluish‐green emission, respectively. These two devices show the high maximum brightness of 81 100 and 70 000 cd m^?2, respectively.     

Highly Thermal Stable and Efficient Organic Photovoltaic Cells with Crosslinked Networks Appending Open‐Cage Fullerenes as Additives

Highly thermal stable organic bulk heterojunction (OBHJ) photovoltaic cells are demonstrated with crosslinkable open‐cage fullerenes ( COF ) as additives in the active layer. Partial incorporation of COF , ≈10–15 wt% with weight ratio of P3HT: PC₆₁BM = 1:0.9, builds up three‐dimensional local borders upon heating treatment at 150 °C for 10 min. This process induces crosslinking chemical reaction through activating the styryl moiety in COF and reduces phase aggregation rates of fullerenes materials. Supported by statistics of devices degradation data analysis and optical microscopy study, the devices with COF show longer lifetime with keeping their efficiency (t = 144 h) under accelerated heating test at 150 °C, while PCE of normal devices without COF drop dramatically. These results demonstrate that the thermally crosslinkable COF is an excellent additive for highly thermal stable and durable OPVs applications.     

Utilizing a Spiro TADF Moiety as a Functional Electron Donor in TADF Molecular Design toward Efficient “Multichannel” Reverse Intersystem Crossing

Designing thermally activated delayed fluorescence (TADF) materials with an efficient reverse intersystem crossing (RISC) process is regarded as the key to actualize efficient organic light‐emitting diodes (OLEDs) with low efficiency roll‐off. Herein, a novel molecular design strategy is reported where a typical TADF material 10‐phenyl‐10H, 10′H‐spiro[acridine‐9, 9′‐anthracen]‐10′‐one (ACRSA) is utilized as a functional electron donor to design TADF materials of 2,4,6‐triphenyl‐1,3,5‐triazine(TRZ)‐p‐ACRSA and TRZ‐m‐ACRSA. It is unique that the intramolecular charge transfer of the ACRSA moiety and the intramolecular and through‐space intermolecular charge transfer between the TRZ and ACRSA moieties, provide a “multichannel” effect to enhance the rate of the reverse intersystem crossing process (k_risc) exceeding 10^?6 s^?1. TADF OLEDs based on TRZ‐p‐ACRSA as an emitter show a maximum external quantum efficiency (EQE) of 28% with reduced efficiency roll‐off (EQEs of 27.5% and 22.1% at 100 and 1000 cd m^?2, respectively). Yellow phosphorescent OLEDs utilizing TRZ‐p‐ACRSA as a host material show record‐high EQE of 25.5% and power efficiency of 115 lm W^?1, while phosphorescent OLEDs based on TRZ‐m‐ACRSA show further lower efficiency roll‐off with EQEs of 25.2%, 24.3%, and 21.5% at 100, 1000, and 10 000 cd m^?2, respectively.     

Low-temperature cross-linkable hole transporting materials through chemical doping for solution-processed green PHOLEDs

Since the inter-layer mutual solubility is an obstacle to the development of solution-processed OLED, cross-linking is considered to be the best method to obtain solvent resistance. Vinyl is the most widely reported crosslinking group, but a problem raised that crosslinking usually need a high temperature. Here, two vinyl-crosslinked hole transporting materials, 3,3'-(1,3,4-oxadiazole-2,5-diyl)bis (N-phenyl-N-(4-vinylphenyl)aniline) (OXZ-VPAN), 3,3'-(4-phenyl-4H-1,2,4-triazole-3,5-diyl)bis (N-phenyl-N-(4-vinylphenyl)aniline) (TRZ-VPAN) were designed and synthesized. The introduction of pentaerythritol tetra(3-mercaptopropionate) (PETMP) and vinyl groups by thiol-ene reaction to reduce the crosslinking temperature. As a result, crosslinking can be achieved at 120 °C with the solvent resistance higher than 99%. The surface morphology of the films before and after crosslinking were characterized by atomic force microscope, and it was found that the roughness of the film was improved after dopped with PETMP. The solution-processed green phosphorescent OLEDs devices based on the obtained HTM exhibit excellent performance. Maximum current efficiency of 57.1 cd A⁻¹ and external quantum efficiency of 16.0% (Ir (mppy)₃) are obtained when OXZ-VPAN served as HTL. This low temperature feasible cross-linking process to prepare HTLs promotes the development solution-processed OLEDs.     

Multifunctional Crosslinkable Iridium Complexes as Hole Transporting/Electron Blocking and Emitting Materials for Solution‐Processed Multilayer Organic Light‐Emitting Diodes

Here, a new series of crosslinkable heteroleptic iridium (III) complexes for use in solution processed phosphorescent organic light emitting diodes (OLEDs) is reported. These iridium compounds have the general formula of (PPZ‐VB)₂Ir(CˆN), where PPZ‐VB is phenylpyrazole (PPZ) vinyl benzyl (VB) ether; and the CˆN ligands represent a family of four different cyclometallating ligands including 1‐phenylpyrazolyl (PPZ) (1), 2‐(4,6‐difluorophenyl)pyridyl (DFPPY) (2), 2‐(p‐tolyl)pyridyl (TPY) (3), and 2‐phenylquinolyl (PQ) (4). With the incorporation of two crosslinkable VB ether groups, these compounds can be fully crosslinked after heating at 180 °C for 30 min. The crosslinked films exhibit excellent solvent resistance and film smoothness which enables fabrication of high‐performance multilayer OLEDs by sequential solution processing of multiple layers. Furthermore, the photophysical properties of these compounds can be easily controlled by simply changing the cyclometallating CˆN ligand in order to tune the triplet energy within the range of 3.0–2.2 eV. This diversity makes these materials not only suitable for use in hole transporting and electron blocking but also as emissive layers of several colors. Therefore, these compounds are applied as effective materials for all‐solution processed OLEDs with (PPZ‐VB)₂IrPPZ (1) acting as hole transporting and electron blocking layer and host material, as well as three other compounds, (PPZ‐VB)₂IrDFPPY ( 2 ), (PPZ‐VB)₂IrTPY(3), and (PPZ‐VB)₂IrPQ( 4 ), used as crosslinkable phosphorescent emitters.     

Phosphorescent dye-doped hole transporting layer for organic light-emitting diodes

Hole transport materials are critical to the performance of organic light-emitting diodes (OLEDs). While 1,1-bis(di-4-tolylaminophenyl)cyclohexane (TAPC) with a high triplet energy is widely used for high efficiency phosphorescent OLEDs, devices using TAPC as a hole transport layer (HTL) have a short operating lifetime due to the build-up of trapped charges at the TAPC/emitting layer (EML) interface during device operation. In this work, to solve the operating stability problem, instead of using conventional HTLs, we use a(fac-tris(2-phenylpyridine)iridium (III))(Ir(ppy)₃) doped layer as an HTL to replace the conventional HTLs. Because of the hole injecting and transporting abilities of the phosphorescent dye, holes can be directly injected into the emitting layer without an injection barrier. OLEDs based on a phosphorescent dye-doped HTL show significant improvement in operational stability without loss of efficiency.     

Synthesis and characterisation of a modified crosslinkable polyurethane non-linear optical polymer

The hydroxyl groups formed during the reaction of DGEBA (diglycidyl ether of bisphenol A) and aniline are used for the first time to form crosslinkable polyurethane. The very active diisocyanate groups as a pure reagent are only introduced to the reaction system at the last step of the crosslinking reaction, which greatly improves the preparation procedure. A very good film-forming property was found and a d₃₃ value as high as 320 pm V⁻ was measured for the poled polymer film. Copyright © 2000 John Wiley & Sons, Ltd.     

Efficient Organic Light‐Emitting Diodes based on Sublimable Charged Iridium Phosphorescent Emitters

The synthesis and characterization of two new phosphorescent cationic iridium(III) cyclometalated diimine complexes with formula [Ir( L )₂(N‐N)]⁺(PF₆^–) ( HL = (9,9‐diethyl‐7‐pyridinylfluoren‐2‐yl)diphenylamine); N‐N = 4,4′‐dimethyl‐2,2′‐bipyridine ( 1 ), 4,7‐dimethyl‐1,10‐phenanthroline ( 2 )) are reported. Both complexes are coordinated by cyclometalated ligands consisting of hole‐transporting diphenylamino (DPA)‐ and fluorene‐based 2‐phenylpyridine moieties. Structural information on these heteroleptic complexes has been obtained by using an X‐ray diffraction study of complex 2 . Complexes 1 and 2 are morphologically and thermally stable ionic solids and are good yellow phosphors at room temperature with relatively short lifetimes in both solution and solid phases. These robust iridium complexes can be thermally vacuum‐sublimed and used as phosphorescent dyes for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs). These devices doped with 5 wt % 1 can produce efficient electrophosphorescence with a maximum brightness of up to 15 610 cd m^–2 and a peak external quantum efficiency of ca. 7 % photons per electron that corresponds to a luminance efficiency of ca. 20 cd A^–1 and a power efficiency of ca. 19 lm W^–1. These results show that charged iridium(III) materials are useful alternative electrophosphors for use in evaporated devices in order to realize highly efficient doped OLEDs.     

Achieving High‐Performance Nondoped OLEDs with Extremely Small Efficiency Roll‐Off by Combining Aggregation‐Induced Emission and Thermally Activated Delayed Fluorescence

Luminescent materials with thermally activated delayed fluorescence (TADF) can harvest singlet and triplet excitons to afford high electroluminescence (EL) efficiencies for organic light‐emitting diodes (OLEDs). However, TADF emitters generally have to be dispersed into host matrices to suppress emission quenching and/or exciton annihilation, and most doped OLEDs of TADF emitters encounter a thorny problem of swift efficiency roll‐off as luminance increases. To address this issue, in this study, a new tailor‐made luminogen (dibenzothiophene‐benzoyl‐9,9‐dimethyl‐9,10‐dihydroacridine, DBT‐BZ‐DMAC) with an unsymmetrical structure is synthesized and investigated by crystallography, theoretical calculation, spectroscopies, etc. It shows aggregation‐induced emission, prominent TADF, and interesting mechanoluminescence property. Doped OLEDs of DBT‐BZ‐DMAC show high peak current and external quantum efficiencies of up to 51.7 cd A^?1 and 17.9%, respectively, but the efficiency roll‐off is large at high luminance. High‐performance nondoped OLED is also achieved with neat film of DBT‐BZ‐DMAC, providing excellent maxima EL efficiencies of 43.3 cd A^?1 and 14.2%, negligible current efficiency roll‐off of 0.46%, and external quantum efficiency roll‐off approaching null from peak values to those at 1000 cd m^?2. To the best of the authors' knowledge, this is one of the most efficient nondoped TADF OLEDs with small efficiency roll‐off reported so far.     

Sub‐3 V ZnO Electrolyte‐Gated Transistors and Circuits with Screen‐Printed and Photo‐Crosslinked Ion Gel Gate Dielectrics: New Routes to Improved Performance

A facile, high‐resolution patterning process is introduced for fabrication of electrolyte‐gated transistors (EGTs) and circuits using a photo‐crosslinkable ion gel and stencil‐based screen printing. The photo‐crosslinkable gel is based on a triblock copolymer incorporating UV‐sensitive terminal azide functionality and a common ionic liquid. Using this material in conjunction with conventional photolithography and stenciling techniques, well‐defined 0.5–1 μm thick ion gel films are patterned on semiconductor channels as narrow as 10 μm. The resulting n‐type ZnO EGTs display high electron mobility (>2 cm² Vs^?1) and on/off current ratios (>10⁵). Further, EGT‐based inverters exhibit static gains >23 at supply voltages below 3 V, and five‐stage EGT ring oscillator circuits display dynamic propagation delays of 50 μs per stage. In general, the screen printing and photo‐crosslinking strategy provides a clean room‐compatible method to fabricate EGT circuits with improved sensitivity (gain) and computational power (gain × oscillating frequency). Detailed device analysis indicates that significantly shorter delay times, of order 1 μs, can be obtained by improving the ion gel conductance.     

Crosslinkable TAPC‐Based Hole‐Transport Materials for Solution‐Processed Organic Light‐Emitting Diodes with Reduced Efficiency Roll‐Off

1‐Bis[4‐[N,N‐di(4‐tolyl)amino]phenyl]‐cyclohexane (TAPC) has been widely used in xerography and organic light‐emitting diodes (OLEDs), but derivatives are little known. Here, a new series of solution‐processable, crosslinkable hole conductors based on TAPC with varying highest occupied molecular orbital (HOMO) energies from ?5.23 eV to ?5.69 eV is implemented in blue phosphorescent OLEDs. Their superior perfomance compared with the well‐known N4,N4,N4′,N4′‐tetraphenylbiphenyl‐4,4′‐diamine (TPDs) analogues regarding hole‐injection and mobility, electron and exciton blocking capabilities, efficiency, and efficiency roll‐off is demonstrated. Overall, the TAPC‐based devices feature higher luminous and power efficiency over a broader range of brightness levels and reduced efficiency roll off. A systematic broadening of the emission zone is observed as the hole‐injection barrier between the anode and the hole‐transporting layer increased.     

Block Copolymer Permeable Membrane with Visualized High‐Density Straight Channels of Poly(ethylene oxide)

A simple fabrication, scalable to centimeter scale, of a permeable membrane made of block copolymer containing molecular transport channels is demonstrated by coating photo‐crosslinkable liquid‐crystalline block copolymer, consisting of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) bearing stilbene (Stb) mesogens in the side chains (PEO₁₁₄‐b‐PMA(Stb)₅₂), onto a sacrificial cellulose acetate film substrate. After thermal annealing, perpendicularly aligned and hexagonally arranged PEO cylindrical domains with a surface density of 10¹¹ cm^?2 were formed and then fixed efficiently by photo‐crosslinking the stilbene moieties in the PMA(Stb) domains by [2 + 2] dimerization. The fully penetrating straight PEO cylindrical domains across the 480‐nm‐thick membrane were well‐defined and visualized as molecule‐transport channels. After exfoliated by removal of the cellulose acetate layer, the membrane could be transferred onto another substrate by either scooping or a horizontal lifting method. Throughout the processes, the fully penetrating PEO channels across the membrane are preserved to open at both ends. A simple permeation experiment demonstrates that rhodamine dyes permeate efficiently through the PEO cylindrical channels of the annealed membrane but not across a non‐annealed one.     

Low Roll‐Off and High Efficiency Orange Organic Light Emitting Diodes with Controlled Co‐Doping of Green and Red Phosphorescent Dopants in an Exciplex Forming Co‐Host

An exciplex forming co‐host is introduced in order to fabricate orange organic light‐emitting diodes (OLEDs) with high efficiency, low driving voltage and an extremely low efficiency roll‐off, by the co‐doping of green and red emitting phosphorescence dyes in the host. The orange OLEDs achieves a low turn‐on voltage of 2.4 V, which is equivalent to the triplet energy gap of the phosphorescent‐green emitting dopant, and a very high external quantum efficiency (EQE) of 25.0%. Moreover, the OLEDs show low efficiency roll‐off with an EQE of over 21% at 10 000 cdm^?2. The device displays a very good orange color (CIE of (0.501, 0.478) at 1000 cdm^?2) with very little color shift with increasing luminance. The transient electroluminescence of the OLEDs indicate that both energy transfer and direct charge trapping takes place in the devices.     

Synthesis,Characterization, and Field‐Effect Transistor Performance of Thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene Derivatives

The synthesis, characterization, and field‐effect transistor (FET) properties of a new class of thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene derivatives are described. The optical spectra of their films show the presence of stronger interactions between molecules in the solid state. Thermal analyses reveal that the three materials are thermally stable and have no phase transitions at low temperature. The crystal structures are determined, and show π‐stacked structures and intermolecular S···S contacts. These organic materials exhibit p‐type FET behavior with hole mobilities as high as 0.14 cm² V^?1 s^?1 and an on/off current ratio of 10⁶. These results indicate that thieno[3,2‐b]thieno [2′,3′:4,5]thieno[2,3‐d]thiophene, as a linear π‐conjugated system, is an effective building block for developing high‐performance organic semiconductors.     

Exciton–Exciton Annihilation in Thermally Activated Delayed Fluorescence Emitter

Recent studies have demonstrated that in thermally activated delayed fluorescence (TADF) materials, efficient reverse intersystem crossing occurs from nonradiative triplet exited states to radiative singlet excited states due to a small singlet–triplet energy gap. This reverse intersystem crossing significantly influences exciton annihilation processes and external quantum efficiency roll‐off in TADF based organic light‐emitting diodes (OLEDs). In this work, a comprehensive exciton quenching model is developed for a TADF system to determine singlet–singlet, singlet–triplet, and triplet–triplet annihilation rate constants. A well‐known TADF molecule, 3‐(9,9‐dimethylacridin‐10(9H)‐yl)‐9H‐xanthen‐9‐one (ACRXTN), is studied under intensity‐dependent optical and electrical pulse excitation. The model shows singlet–singlet annihilation dominates under optically excited decays, whereas singlet–triplet annihilation and triplet–triplet annihilation have strong contribution in electroluminescence decays under electrical pulse excitation. Furthermore, the efficiency roll‐off characteristics of ACRXTN OLEDs at steady state is investigated through simulation. Finally, singlet and triplet diffusion length are calculated from annihilation rate constants.     

Thermally Activated Delayed Fluorescence Conjugated Polymers with Backbone‐Donor/Pendant‐Acceptor Architecture for Nondoped OLEDs with High External Quantum Efficiency and Low Roll‐Off

Most thermally activated delayed fluorescence (TADF) emitters have to be doped in the host for fabricating efficient organic light‐emitting diodes (OLEDs) and always suffer from quick efficiency roll‐off at high brightness, which severely affect their commercial application in display and lighting fields. In the work, a series of the polymers are synthesized by copolymerization of two carbazole monomers and one acridine derivative monomer containing benzophenone acceptor group. The obtained polymers therefore possess a conjugated backbone with carbazole/acridine moieties and benzophenone pendant to form the twisted donor/acceptor structure. Consequently, the TADF features inherited from the acridine derivative are maintained and improved by managing the content of acridine derivative monomer in the polymers. Solution‐processed OLEDs obtained from using neat polymer films exhibit comparable performance with organic TADF small molecules, achieving a maximum external quantum efficiency (EQE) of 18.1% and a very slow roll‐off with EQE of 17.8% at the luminance of 1000 cd m⁻².     

An Effective Approach toward Yellow-to-Orange Multi-Resonance TADF Emitters by Integrating Strong Electron Donor into B/N-Based Polycyclic Architecture: High Performance OLEDs with Nearly 40% EQE

B/N-based multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters and the corresponding narrow band emissive organic light-emitting diodes (OLEDs) exhibit great potential for next-generation high-resolution displays. Nonetheless, designing MR-TADF emitters with emission wavelength over 550 nm remains challenging. Herein, an effective approach toward yellow-to-orange MR-TADF emitters by integrating a strong electron-donating indolophenazine building block into the B/N-doped polycyclic aromatic hydrocarbons is proposed. The investigation of photophysical properties reveals that the electron-donating difference between the donor segments of MR framework has a dramatic influence on the luminescent features, including the emission wavelength and full-width at half-maximum (FWHM). These TADF emitters display excellent photophysical characteristics such as near-unity photoluminescence quantum yields and almost 100% horizontal dipole ratio. As a result, yellow and orange OLEDs employing these emitters achieve state-of-the-art device performances with an ultrahigh external quantum efficiency of up to nearly 40%, power efficiency of 163 lm W⁻¹, and luminance close to 120 000 cd m⁻², which set a record among MR-TADF based OLEDs with emission peaks over 550 nm. More impressively, the fabricated device presents outstanding operational stability of LT₉₉ over 110 h at the initial brightness of 3000 cd m⁻².     

Platinum Binuclear Complexes as Phosphorescent Dopants for Monochromatic and White Organic Light‐Emitting Diodes

Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula C^∧NPt(μ‐pz)₂PtC^∧N (where C^∧N = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C^2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m^–2, a brightness of 3900 Cd m^–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (～ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (～ 5 %) and brightness (～ 600 Cd m^–2 at 10 V).     

Highly Efficient Three Primary Color Organic Single‐Crystal Light‐Emitting Devices with Balanced Carrier Injection and Transport

Organic single crystals have a great potential in the field of organic optoelectronics because of their advantages of high carrier mobility and high thermal stability. However, the application of the organic single crystals in light‐emitting devices (OLEDs) has been limited by single‐layered structure with unbalanced carrier injection and transport. Here, fabrication of a multilayered‐structure crystal‐based OLED constitutes a major step toward balanced carrier injection and transport by introducing an anodic buffer layer and electron transport layer into the device structure. Three primary color single‐crystal‐based OLEDs based on the multilayered structure and molecular doping exhibit a maximum luminance and current efficiency of 820 cd cm^?2 and 0.9 cd A^?1, respectively, which are the highest performance to date for organic single‐crystal‐based OLEDs. This work paves the way toward high‐performance organic optoelectronic devices based on the organic single crystals.