Excellent Electroluminescence Research Articles

Metal Halide Perovskite Single Crystals toward Electroluminescent Applications

AbstractMetal halide perovskite single crystals (MHP SCs) have attracted extensive attention due to their superior properties, such as higher carrier mobility, longer carrier diffusion length, and better stability than their polycrystalline counterparts. In particular, the suppression of ion migration and Auger recombination endows MHP SCs with excellent electroluminescence (EL) properties, thus holding great potential for highly efficient and stable light‐emitting devices. In this review, general overview of MHP crystal structures are begin, and highlight the merits of MHP SCs in terms of outstanding optoelectronic properties and high stability. Then, appropriate growth methods of high‐quality, thickness‐controlled MHP SCs for EL device applications are systematically summarized. Subsequently, recent advancements in developing MHP SC‐based perovskite light‐emitting diodes (PeLEDs) are discussed, and the effective strategies to further enhance the device performance are reviewed. Moreover, the potential application of MHP SCs for electrically pumped lasers is highlighted. Finally, the review is concluded with a detailed account of the current challenges and a perspective on the key approaches and opportunities on the optimization of SC growth, the improvement of device performance and the integration of SC‐based optoelectronic devices.

Improving the Electroluminescence Properties of New Chrysene Derivatives with High Color Purity for Deep-Blue OLEDs.

Two blue-emitting materials, 4-(12-([1,1':3',1″-terphenyl]-5'-yl)chrysen-6-yl)-N,N-diphenylaniline (TPA-C-TP) and 6-([1,1':3',1″-terphenyl]-5'-yl)-12-(4-(1,2,2-triphenylvinyl)phenyl)chrysene (TPE-C-TP), were prepared with the composition of a chrysene core moiety and terphenyl (TP), triphenyl amine (TPA), and tetraphenylethylene (TPE) moieties as side groups. The maximum photoluminescence (PL) emission wavelengths of TPA-C-TP and TPE-C-TP were 435 and 369 nm in the solution state and 444 and 471 nm in the film state. TPA-C-TP effectively prevented intermolecular packing through the introduction of TPA, a bulky aromatic amine group, and it showed an excellent photoluminescence quantum yield (PLQY) of 86% in the film state. TPE-C-TP exhibited aggregation-induced emission; the PLQY increased dramatically from 0.1% to 78% from the solution state to the film state. The two synthesized materials had excellent thermal stability, with a high decomposition temperature exceeding 460 °C. The two compounds were used as emitting layers in a non-doped device. The TPA-C-TP device achieved excellent electroluminescence (EL) performance, with Commission Internationale de L'Eclairage co-ordinates of (0.15, 0.07) and an external quantum efficiency of 4.13%, corresponding to an EL peak wavelength of 439 nm.

Novel green/red oxyfluoride phosphors with excellent optical properties for near-UV excited white light emitting diode

Novel eye-sensitive Ba3Nb2O2F12(H2O)2:Tb3+ green and Ba3Nb2O2F12(H2O)2:Mn4+ red oxyfluoride phosphors with extremely strong absorption in the UV region were designed and synthesized by simple co-precipitation strategy. Particularly, Tb3+ ions were doped in this matrix for the first time, which greatly improves their absorption efficiency in the near ultraviolet region (367 nm) and emits sharp green light (544 nm). In addition, the Ba3Nb2O2F12(H2O)2:Mn4+ red phosphors have strong zero phonon line (ZPL) emission at 625 nm, which is conducive to improving the sensitivity of human eye and color purity. Meanwhile, the optical properties of the red phosphor are significantly enhanced via doping K+ cations as charge compensators. Crystal field environment and nephelauxetic effect of the as-prepared phosphors before and after K+ cation doping were systematically analyzed. Moreover, these synthesized red/green phosphors have good thermal stability and moisture resistance. Remarkably, the as-prepared Ba3Nb2O2F12(H2O)2:5%Mn4+ or K0.9Ba2.1Nb2O2F12(H2O)2:5%Mn4+ red phosphors can be directly mixed with the as-synthesized Ba3Nb2O2F12(H2O)2:13%Tb3+ green phosphor coating on 365 nm near-ultraviolet LED chip to package WLED devices with excellent electroluminescence performance. These findings are conducive to opening an avenue for screening the unique structure of optical materials.

All-fluorescent white organic light-emitting diodes employing a deep-blue HLCT material simultaneously as emitter and host achieving excellent electroluminescence performance with efficiency roll-off

Simultaneously achieving high efficiency and small efficiency roll-off remains a huge challenge for white organic light-emitting diodes (OLEDs), which greatly restricts their industrial application in the lighting field. Recently developed hybridized local and charge transfer (HLCT) materials have a “hot exciton” channel, which can maximize the utilization rate of excitons and suppress efficiency roll-off via rapid reverse intersystem crossing (RISC) from high-lying triplet state (Tn, n ≥ 2) to singlet state (S1). In this work, employing blue HLCT material pCzAnN as the sensitizing host, by precise concentration management, the traditional fluorescent C545T- and DCJTB-based green and orange-red OLEDs are first fabricated, which achieve the maximum external quantum efficiency (EQE) exceeding the theoretical limit of 5 %, reaching 8.51 % and 6.64 %, respectively. On this basis, by strategic device structure design, all-fluorescent two- and three-color white OLEDs are demonstrated having pCzAnN simultaneously as blue emitter and sensitizing host of C545T and DCJTB. The resulting two- and three-color white devices obtain maximum EQE beyond 5 %. What's more, all three-color white devices exhibit extremely small efficiency roll-off, where the efficiency drops are less than 1 % at a practical luminance of 1000 cd/m2, which is comparable to the best works reported in the literatures. At the same time, the optimized three-color white device realizes ideal white emission, in which the electroluminescence (EL) spectra contain three almost equal intensity emission wavebands accompanied by a high color rendering index of 87. Stable EL spectra under a wide luminance range (3863 ∼ 27710 cd/m2) indicate a huge potential application. We believe this work can provide new idea for developing high-efficiency and low roll-off white OLEDs in the future.

Molecular Engineering Modulating the Singlet-Triplet Energy Splitting of Indolocarbazole-Based TADF Emitters Exhibiting AIE Properties for Nondoped Blue OLEDs with EQE of Nearly 20.

The development of efficient blue thermally activated delayed fluorescence (TADF) emitters with an aggregation-induced emission (AIE) nature, for the construction of organic light-emitting diodes (OLEDs), is still insufficient. This can be attributed to the challenges encountered in molecular design, including the inherent trade-off between radiative decay and reverse intersystem crossing (RISC), as well as small singlet-triplet energy splitting (ΔEST) and the requirement for high photoluminescence quantum yields (ΦPL). Herein, we present the design of three highly efficient blue TADF molecules with AIE characteristics by combining π-extended donors with different acceptors to modulate the differences in the electron-donating and electron-withdrawing abilities. This approach not only ensures high emission efficiency by suppressing close π-π stacking, weakening nonradiative relaxation, and enhancing radiative transition but also maintains the equilibrium ratio between the triplet and singlet excitons by facilitating the process of RISC. These emitters exhibit AIE and TADF properties, featuring quick radiative rates and low nonradiative rates. The ΦPL of these emitters reached an impressive 88%. Based on their excellent comprehensive performance, nondoped PICzPMO and PICzPMO OLEDs achieved excellent electroluminescence performance, exhibiting maximum external quantum efficiency (EQEmax) of up to 19.5%, while the doped device achieved a higher EQEmax of 20.8%. This work demonstrated that by fusing π-extended large rigid donors with different acceptors, it is possible to regulate the difference in electron-donating and electron-withdrawing abilities, resulting in a small ΔEST, high ΦPL, and fast RISC process, which is a highly feasible strategy for designing efficient TADF molecules.

Simultaneously Realizing High Efficiency and High Color Rendering Index for Hybrid White Organic Light-Emitting Diodes by Ultra-Thin Design of Delayed Fluorescence Sensitized Phosphorescent Layers.

In consideration of energy economization and light quality, concurrently attaining high external quantum efficiency (ηext ) and high color rendering index (CRI) is of high significance for the commercialization of hybrid white organic light-emitting diodes (WOLEDs) but is challenging. Herein, a blue luminescent molecule (2PCz-XT) consisting of a xanthone acceptor and two 3,6-diphenylcarbazole donors is prepared, which exhibits strong delayed fluorescence, short delayed fluorescence lifetime, and excellent electroluminescence property, and can sensitize green, orange, and red phosphorescent emitters efficiently. By employing 2PCz-XT as sensitizer and phosphorescent emitters as dopants, efficient two-color and three-color WOLED architectures with ultra-thin phosphorescent emitting layers (EMLs) are proposed and constructed. By incorporating a thin interlayer to modulate exciton recombination zone and reduce exciton loss, high-performance three-color hybrid WOLEDs are finally achieved, providing a high ηext of 26.8% and a high CRI value 83 simultaneously. Further configuration optimization realizes a long device operational lifetime. These WOLEDs with ultra-thin phosphorescent EMLs are among the state-of-the-art hybrid WOLEDs in the literature, demonstrating the success and applicability of the proposed device design for developing robust hybrid WOLEDs with superb efficiency and color quality.

Efficient non-doped sky-blue fluorescent organic light emitting devices based on cyanopyridine-containing anthracene derivatives

Two new cyanopyridine-containing anthracene derivatives with asymmetrical donor-π-acceptor (D-π-A) molecule structure have been successfully synthesized by Suzuki coupling reaction, namely 4-(10-(9-phenyl-9H-carbazol-3-yl)anthracen -9-yl)benzonitrile (3CzAnPyCN) and 4-(10-(4-(9H-carbazol-9-yl)phenyl)anthracen -9-yl)benzonitrile (pCzAnPyCN). The non-doped organic light emitting devices (OLEDs) using 3CzAnPyCN and pCzAnPyCN as emitters simultaneously achieved high efficiency stable sky-blue luminescence, corresponding to the maximum external quantum efficiency (EQE) of 8.07% and 8.13% with the Commission International de L'Eclairage (CIE) coordinates of (0.18, 0.35) and (0.16, 0.24), respectively. In addition, extremely low efficiency roll-offs were also evaluated in this work. The EQE values remained as high as 7.80% and 7.88% at the luminance of 1000 cd/m2, 7.31% and 6.95% at the luminance of 10000 cd/m2 for 3CzAnPyCN and pCzAnPyCN, respectively. It is found, by photophysical experiments and density functional theory analysis, that the excited state property of the luminogens revealed that the “hot excitons” induced reverse intersystem crossing (RISC) played a crucial role in improving efficiency. Such an excellent electroluminescence (EL) performance achieved in these non-doped OLEDs is among the highest values based on sky-blue fluorescent materials, potential for future optical applications.

Ionic Liquid-Induced Multisite Synergistic Interactions for Highly Efficient Inverted Perovskite Solar Cells.

The interfacial properties of p-i-n inverted perovskite solar cells (PSCs) play a key role in further improving the photovoltaic performance of PSCs. Herein, multisite synergistic interactions were constructed using ionic liquids (ILs) prepared by mixing urea and choline chloride (ChCl) to substantially improve the interfacial properties of inverted PSCs. Systematically theoretical calculations and experimental studies are comprehensively performed, which reveal that the C═O···Pb2+ coordination interaction, N-H···I hydrogen bond, and Cl-Pb bond could be simultaneously formed between the perovskites and IL, and Ch in IL could interact with the perovskite by occupying the formamidinium site. Meanwhile, -OH/π and -NH/π interactions could be formed between -OH and -NH in IL and the phenyl group in PTAA, respectively. These multisite synergistic interactions are beneficial to improve the perovskite film quality and interfacial properties of inverted PSCs, which could greatly suppress nonradiative recombination within the PSCs. Consequently, the inverted PSCs show an impressive efficiency of 22.4% and an excellent electroluminescence efficiency of 3.7%.

Low-trigger voltage and efficient phosphorescent organic light-emitting diodes with bipolar TADF host

Thermally activated delayed fluorescence (TADF) materials have continued to attract interest due to their rapid improvements in efficiency, non-toxic and potential to be manufactured at energy-saving organic light-emitting diode for full-color display and solid-state lighting. Here, The bipolar and electroluminescence (EL) characteristics of TADF host, 11-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-12,12-dimethyl-11,12-dihydroindeno[2,1-a]carbazole (DPDDC), were investigated. By incorporating the phosphorescent tris[2-(p-tolyl)pyridine]iridium(III) [Ir(mppy)3] dopant into the matrix, DPDDC showed more excellent EL performance compared with the typical 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host. The turn-on voltage for phosphorescent organic light-emitting diodes (PhOLEDs) was decreased to 2.2 V from 2.5 V by exploiting the TADF host instead of CBP. Crucially, we found that the ratio of Ir(mppy)3 in TADF host plays a significant role in EL process. Remarkable low efficiency roll-off was achieved with above 90% of the current efficiency maintained even at a brightness of 3000 cd m−2, along with high power efficiency of 84.8 lm·W−1 and the external quantum efficiency of 20.6% for DPDDC: 5 wt% Ir(mppy)3-based device.

Phase Distribution Manipulation through Molecular Interaction Enables Efficient Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) metal halide perovskites exhibit excellent electroluminescence (EL) performance promising for display and lighting applications, which benefits from the quantum and/or dielectric confinement effects as well as the unique energy-funneling process. However, the inefficient energy transfer caused by the intricate phase distribution with different thick nanoplatelets (n-values), as well as the existence of numerous defects, could deteriorate the EL performance of the resulting perovskite light-emitting diodes (PeLEDs). Here, a multifunctional small molecule, bistrifluoromethanesulfonimide lithium (LiTFSI), was introduced to address the above issues. The strongly electronegative fluorine atoms in LiTFSI form hydrogen bonding interactions with the ammonium heads of organic spacers, which suppress the formation of perovskite ultrathin nanoplatelet phases with small n-values, thus smoothing the energy transfer process. Meanwhile, the Lewis base sulfur oxide groups are capable of effectively passivating the uncoordinated lead ion defects and then reducing nonradiative recombination loss. Eventually, a green emission quasi-2D PeLED with an external quantum efficiency of 21.0% was achieved. This work provides a facile method to boost the performance of quasi-2D PeLEDs.

Through-Space Conjugated Molecule with Dual Delayed Fluorescence and Room-Temperature Phosphorescence for High-Performance OLEDs

Purely organic materials with room-temperature phosphorescence usually have much longer triplet state lifetimes than noble-metal containing phosphorescent materials, which lead to severe exciton quenching and inferior electroluminescence (EL) performance when applied in organic light-emitting diodes (OLEDs). Herein, a novel through-space conjugated molecule (2,3-PICz-XT) with dual delayed fluorescence and room-temperature phosphorescence is developed. Owing to suitable energy levels and strong spin–orbit coupling among excited states, 2,3-PICz-XT has short phosphorescence lifetimes at microsecond scale and high photoluminescence quantum yields in neat and doped films. 2,3-PICz-XT can function as efficient emitters in OLEDs, providing high external quantum efficiencies (ηexts) of up to 32.73% with small efficiency roll-offs. It can also efficiently sensitize various phosphorescent and thermally activated delayed fluorescence (TADF) materials to yield excellent EL performances. Impressively, the hyperfluorescence OLEDs using 2,3-PICz-XT as sensitizer for multiple resonance TADF materials attain narrow EL spectra and greatly improved ηexts over 35%. To the best of our knowledge, 2,3-PICz-XT is the most efficient emitter and sensitizer ever reported for dual delayed fluorescence and phosphorescence materials.

High-performance non-doped near ultraviolet OLEDs with the EQE ∼ 6 % and CIEy ∼ 0.03 from high-lying reverse intersystem crossing

Developing high-performance organic fluorophors with short-wavelength emission is both significant and challenging subject in the application of organic light-emitting diodes (OLEDs). In this work, we proposes a “coupling hardness with distortion” design concept to construct an efficient near ultraviolet (NUV) fluorophor mP2MPC with 1,4-dimethyl-2,5-diphenylbenzene as a rotatable bridge via the meta-positons linking rigid and bulky phenanthroimidazole and carbazole groups. As a result, the non-doped OLED with it as emitter not only exhibits an emission peak at 395 nm with the Commission Internationale de l’éclairage coordinates of (0.163, 0.028), but also realizes a high forward-viewing external quantum efficiency of 6.09 % due to the high-lying reverse intersystem crossing. The value still keeps as high as 5.56 % at 1000 cd m−2, showing a small efficiency roll-off. This is one of the highest efficiencies among the non-doped devices with the electroluminescence peak below 400 nm. Moreover, the green and red phosphorescent OLEDs with mP2MPC as host can also show excellent electroluminescence performance with the forward-viewing external quantum efficiencies over 21.5 %, illustrating that mP2MPC should be a prospective material for OLEDs.

Strategies to Improve the Stability of Perovskite Light-Emitting Diodes: Progress and Perspective.

Perovskite light-emitting diodes (PeLEDs) featuring excellent electroluminescent (EL) characteristics and facile production have been emerging as promising candidates for next-generation high-definition displays. In recent years, tremendous advances have been achieved in the EL efficiency of PeLEDs. However, their poor operational stability impedes practical applications. Particularly, the severe spectral instability of pure-blue and pure-red PeLEDs lags far behind the requirements of commercial displays. In this Perspective, the critical factors related to device degradation are first summarized, including perovskite crystal defects, unbalanced charge injection, Auger recombination, and Joule heating. Then, the recent progress in improving the operational and spectral stabilities is reviewed in categories. Considering the present achievements, we provide potential research directions for further development of stable PeLEDs.

Y‐Shaped Pyrene‐Based Aggregation‐Induced Emission Blue Emitters for High‐Performance OLED Devices

AbstractThe proposed concept of aggregation‐induced emission (AIE) has offered an efficient strategy to design high‐performance luminescent materials. Herein, three blue emitters containing a pyrene core decorated with either triphenylamine or tetraphenylethylene units are presented. The designed compoundsPy‐TPAandPy‐2TPEare AIE or active materials with blue emission from 464 to 478 nm in the solid state, whereasPy‐2TPAis not. Moreover, the enhanced thermal stability of compoundsPy‐TPAandPy‐2TPEallows for their utilization as emitter layers for the fabrication of blue organic light‐emitting diode (OLED) devices. The devices exhibit excellent electroluminescence emission with maximum λmax emin the range 456–482 nm with a maximum external quantum efficiency of 7.27%, high exciton utilization efficiency (77.3%), and low turn‐on voltage (≤3.1 V), as well as low‐efficiency roll‐off. Theoretical calculations reveal that the high exciton utilization efficiency (ƞr) originates from the triplet excitons at T2to the lowest single excited (S1) state via a reverse intersystem crossing process following the principle of the “hot exciton” mechanism. This article not only provides powerful evidence revealing the advantages of pyrene‐based AIEgens for OLED applications, but also offers a new approach for designing pyrene‐based “hot exciton” materials for next‐generation OLEDs.

Enhanced ultraviolet electroluminescence performance from p-NiO/n-GaN heterojunctions by using i-Ga2O3 as electron blocking layer

In recent years, GaN materials have been applied to the field of optoelectronic devices due to their excellent photoelectric properties, especially in the field of light-emitting diodes, which has attracted considerable attention. In this article, we use structural engineering methods to further improve the performance of GaN-based ultraviolet light-emitting diodes. The magnetron sputtering and annealing treatment were used to prepare ultraviolet light-emitting diodes based on p-NiO/i-Ga2O3/n-GaN and p-NiO/n-GaN heterojunction structure. X-ray diffractometer, field emission scanning electron microscope and ultraviolet-visible spectrophotometer were used to study the crystal quality, surface morphology, and optical properties of Ga2O3 film. Compared with the p-NiO/n-GaN heterojunction diode, the p-NiO/i-Ga2O3/n-GaN heterojunction diode exhibits better rectification characteristics and more excellent electroluminescence characteristics. Under the injection voltage of 35 V, the EL spectrum intensity of p-NiO/i-Ga2O3/n-GaN heterojunction diode is nearly 37 times higher than that of p-NiO/n-GaN heterojunction diode. Finally, the working mechanism of the electroluminescence is analyzed in detail through the energy band diagram of the two diodes.

An efficient solution-processable hybridized local and charge-transfer (HLCT)-based deep-red fluorescent emitter for simple structured non-doped OLED

The development of highly efficient deep-red fluorescent emitters is still a challenging task due to their intrinsic low bandgap characteristics resulting in low fluorescence emission in solid-state. Moreover, most of efficient deep-red organic light-emitting diodes (OLEDs) have complex device structures and are fabricated by high-cost vacuum deposition techniques. Herein, a novel solution-processable hybridized local and charge-transfer (HLCT) deep-red fluorescent molecule, TPA-NZF, is designed and synthesized as an emitter for low-cost and simple-structured OLEDs. TPA-NZF comprises a strong electron-deficient naphthothiadiazole (NZ) functionalized with triphenylamine (TPA) as a donor and dioctylfluorene as a solubilizing moiety. The photophysical results and theoretical calculations reveal a strong donor-acceptor feature and deep-red fluorescent emission with a solid-state photoluminescence quantum yield as high as 44%, decent hole-transporting mobility, good film morphology, and thermal and electrochemical stabilities. TPA-NZF is successfully fabricated as a solution-processed non-doped emitter in simple structured OLEDs. The device shows excellent electroluminescence (EL) performance (maximum external quantum efficiency (EQEmax) of 3.59%) and a deep-red emission with CIE coordinates of (0.66, 0.33).

Solution-processed high-performance orange-red organic light-emitting diode (OLED) based on ionic phosphorescent iridium(III) complex

A new and efficient ionic orange-red Ir(III) complex is rationally designed by utilizing 2-(4-chloro-3-(trifluoromethyl)phenyl)-4-methylquinoline and a large conjugated 2,2′-biquinoline as main ligand and ancillary ligand, respectively. The complex shows bright phosphorescence peaking at 583 and 626 nm (shoulder) with high absolute phosphorescent quantum efficiency of 81.3% and moderate emission lifetime of 1.54 μs in dichloromethane solution, which is suitable for fabricating high-performance solution-processed organic light-emitting diode. The device based on this ionic complex exhibits excellent electroluminescence performance, with the maximum luminance, external quantum efficiency, current efficiency, and power efficiency of up to 1209 cd/m2, 10.20%, 21.9 cd/A and 9.57 lm/W, respectively, thereby demonstrating that this new cationic Ir(III) complex possesses tremendous potentials for the future solution-processed electroluminescence.

Multifunctional luminophores with dual emitting cores: TADF emitters with AIE properties for efficient solution- and evaporation-processed doped and non-doped OLEDs

• Three dual emitting core emitters are developed by coupling single core emitters. • The emitters possess high absorption coefficients and PLQY values in neat films. • Photophysical investigations demonstrate both AIE and TADF properties. • Highly efficient OLEDs with ultra-low efficiency roll-offs are achieved. Three novel emitters with dual emitting cores, namely 3,3′,5,5′-tetra(triphenylamine-4-yl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile (DDTPAIPN), 3,3′-di(triphenylamine-4-yl)-5,5′-di(3,5-(9,9′-dicarbazolyl)phenyl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile (DTPAmCPIPN), and 3,3′,5,5′-tetra(3,5-(9,9′-dicarbazolyl)phenyl)-[1,1′-biphenyl]-2,2′,6,6′-tetracarbonitrile (DDmCPIPN) are designed and synthesized by coupling their respective single core emitters. Compared with their single core counterparts, the three novel compounds exhibit significantly improved thermal stability, absorption coefficients, and photoluminescence efficiencies in neat films. Photophysical measurements show that these three emitters exhibit both aggregation-induced emission and thermally activated delayed fluorescence properties, which is beneficial for non-doped organic light-emitting diodes (OLEDs). The new compounds show relatively balanced charge carrier transport abilities as revealed by unipolar devices. The solution- and evaporation-processed doped and non-doped OLEDs made from these three luminophores achieve excellent electroluminescence (EL) performances. The peak current, power, and external quantum efficiencies of a DTPAmCPIPN-based solution-processed doped device reach 59.2 cd A −1 , 61.3 lm W −1 , and 17.2%, respectively, with an emission peak at 548 nm. The evaporation-processed doped device based on DTPAmCPIPN exhibits maximum EL efficiencies of up to 63.7 cd A −1 , 61.1 lm W −1 , and 19.2%. Moreover, the non-doped OLEDs also possess superior EL efficiencies with extremely small efficiency roll-offs. The molecular design strategy in this work is demonstrated to be effective in developing new emitters for efficient and stable OLEDs.

Robust Luminescent Molecules with High-Level Reverse Intersystem Crossing for Efficient Near Ultraviolet Organic Light-Emitting Diodes.

Organic light-emitting diodes (OLEDs) radiating near ultraviolet (NUV) light are of high importance but rarely reported due to the lack of robust organic short-wavelength emitters. Here, we report a short π-conjugated molecule (POPCN-2CP) with high thermal and morphological stabilities and strong NUV photoluminescence. Its neat film exhibits an electroluminescence (EL) peak at 404 nm with a maximum external quantum efficiency (ηext,max ) of 7.5 % and small efficiency roll-off. The doped films of POPCN-2CP in both non-polar and polar hosts at a wide doping concentration range (10-80 wt%) achieve high-purity NUV light (388-404 nm) and excellent ηext,max s of up to 8.2 %. The high-level reverse intersystem crossing improves exciton utilization and accounts for the superb ηext,max s. POPCN-2CP can also serve as an efficient host for blue fluorescence, thermally activated delayed fluorescence and phosphorescence emitters, providing excellent EL performance via Förster energy transfer.

Robust Luminescent Molecules with High‐Level Reverse Intersystem Crossing for Efficient Near Ultraviolet Organic Light‐Emitting Diodes

AbstractOrganic light‐emitting diodes (OLEDs) radiating near ultraviolet (NUV) light are of high importance but rarely reported due to the lack of robust organic short‐wavelength emitters. Here, we report a short π‐conjugated molecule (POPCN‐2CP) with high thermal and morphological stabilities and strong NUV photoluminescence. Its neat film exhibits an electroluminescence (EL) peak at 404 nm with a maximum external quantum efficiency (ηext,max) of 7.5 % and small efficiency roll‐off. The doped films of POPCN‐2CP in both non‐polar and polar hosts at a wide doping concentration range (10–80 wt%) achieve high‐purity NUV light (388–404 nm) and excellentηext,maxs of up to 8.2 %. The high‐level reverse intersystem crossing improves exciton utilization and accounts for the superbηext,maxs. POPCN‐2CP can also serve as an efficient host for blue fluorescence, thermally activated delayed fluorescence and phosphorescence emitters, providing excellent EL performance via Förster energy transfer.