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High‐quality near‐ultraviolet/deep‐blue organic emitters are urgently needed but still rare. Here, three V‐shape donor‐acceptor‐donor (D‐A‐D) emitters based on pyrazine cores, namely, VDMP‐PhCz, VDMP‐36PhCz, and VDMP‐TPA, are designed and synthesized. Their doped devices using a high‐polar host show remarkable electroluminescence (EL) performances with maximum external quantum efficiency (EQE) values up to 7.37%, 7.55%, and 9.03%, and corresponding CIE coordinates of (0.160,0.040), (0.161,0.039), and (0.149,0.072), respectively. Supported by theoretical calculations and experimental results, the high EL performances of these emitters are achieved by their planarized intramolecular charge transfer (PLICT) features, high triplet‐excitons utilization from "hot exciton" channels, and high horizontal dipole orientations. Furthermore, these PLICT‐based emitters can also function as efficient hosts for green or yellow multi‐resonance (MR) narrowband emissive guests, providing high EQEs of over 32% with alleviated efficiency roll‐offs. [ABSTRACT FROM AUTHOR]

"Hot exciton" molecules that allow the transition of excitons from a high‐lying triplet state (Tn, n≥ 2) to singlet states (Sm, m≥1) by a reverse intersystem crossing (hRISC) process have become an effective strategy to achieve high efficiency fluorescence organic light emitting diodes (OLEDs). However, the understanding of the dynamic behavior of the "hot exciton" process is still very lacking. Herein, the exciton dynamics of an aggregation‐induced emission (AIE) molecule TPA‐An‐mPhCz with the "hot exciton" property are deeply investigated, and the proportion between hRISC and internal inversion (IC) of excitons on Tn is successfully quantified by in situ transient electroluminescent measurements and theoretical calculation. It is found that the IC process increases severe energy loss of Tn excitons. By introducing a triplet–triplet annihilation up‐conversion layer in the emissive layer to efficiently recapture the IC excitons and further doping a blue fluorescent emitter in the TPA‐An‐mPhCz layer to achieve high photoluminescence quantum yield (PLQY), the resulting OLED achieves a maximum external quantum efficiency of 12.5% with negligible efficiency roll‐off. More impressively, the operational lifetime LT75 (lifetime to 75% of the initial luminance) of the device with efficient triplets utilization performs a remarkable 116 h under 1000 cd m−2. This work provides the fundamentals for the design of hot exciton materials with efficient exciton utilization to develop efficient blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

Aggregation‐induced emission (AIE) materials are attractive for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) owing to the "hot exciton" process by reverse intersystem crossing (hRISC) and high photoluminescence quantum yields (PLQY). However, the internal conversion (IC) from the high‐lying triplet excitation states (Tn, n≥2) to the lower excited triplet state (Tn‐1) is inevitable, resulting in severe exciton losses. Herein, an effective device structure is designed that reuses the lost triplet excitons caused by IC and realizes the breakthrough in the efficiency of blue fluorescence OLEDs based on AIE molecule as an emitter. The maximum external quantum efficiency reached as high as 14.8% and is kept at 14.4% at the luminance of 1000 cd m−2. In the designed device, a triplet–triplet annihilation (TTA) up‐conversion material 1‐[2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl]pyrene (DMPPP) is introduced into the AIE emitter as a triplet sensitizer to receive the lost triplet excitons, and a thin TTA up‐conversion layer 9‐[4‐(10‐phenyl‐9‐anthryl)phenyl]‐9H‐carbazole (CzPA) is introduced in the middle of the doped layer to form the emissive layer (EML). It is found that the hRISC process of iTPB‐2AC greatly enhances the utilization efficiency of TTA intermediate state ([TT]*) excitons on CzPA to iTPB‐2AC so that the utilization of the lost excitons is maximized. This work establishes physical insights into the AIE emission materials and device fabrication of high‐efficiency blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

The reverse intersystem crossing (RISC) process from triplet to singlet manifold can efficiently improve the efficiencies of organic light‐emitting diodes (OLEDs). The relevant RISC rate (kRISC) is one of the key factors that affect the efficiency roll‐off and stability of devices. Here, a new blue "hot exciton" material, CPPCN, with pyrene as the core, is designed and synthesized. Photophysical studies indicate there are multiple high‐lying triplet states near the lowest singlet excited state (S1) of CPPCN, which facilitate the RISC from the high‐lying triplet state (hRISC) to the S1 state. The corresponding hRISC rate constant is determined to be as high as 2.86 × 108 s−1, a value some two to three orders of magnitude higher than typical thermally activated delayed fluorescence materials emitters. Benefiting from this ultrafast hRISC process, non‐doped blue OLED based on CPPCN reaches a high maximum external quantum efficiency (EQE) of 11.64% with suppressed efficiency roll‐off (begin roll‐off at a high brightness of 3732 cd m−2 and retains EQE >8.5% at 10 000 cd m−2). The T95 lifetime of the CPPCN‐based device with a structure of commercial applications is evaluated to be ≈368 h at 1000 cd m−2. [ABSTRACT FROM AUTHOR]

Triplet–triplet annihilation (TTA) is a feasible approach for utilizing electrically generated triplet excitons in organic light‐emitting diodes. However, low TTA efficiency is often observed in solids. Owing to the optically inaccessible nature of triplets, the main loss routes of the TTA process remain unknown. In this work, three vibrational emission peaks of the first excited triplet state (T1) are identified in the sensitized room‐temperature phosphorescence of TTA molecules. These peaks provide strong evidence of the loss channels of TTA. It is found that the monomolecular recombination of T1 represents an energy‐loss channel that combines the transient photoluminescence of both upconversion fluorescence and phosphorescence. Moreover, the study demonstrates that low‐energy vibrational T1 acts as an energy‐loss channel with only slight contributions to TTA. This work presents constructive insights into the improvement of TTA efficiency in solid films. [ABSTRACT FROM AUTHOR]

High‐performance deep‐blue fluorescent materials matching the required Commission Internationale de l'Eclairage y coordinate value (CIEy) of < 0.08 are much‐needed in organic light‐emitting diodes (OLEDs) for realizing the perfect application of full‐color displays. However, deep‐blue fluorophors commonly show unsatisfactory performance due to the intrinsic large bandgap characteristic. Here, the deep‐blue nondoped OLED with the good CIE coordinates of (0.15, 0.07) and external quantum efficiency (EQE) of ≈9% is achieved based on a multifunctional and efficient anthracene‐based fluorophor (2M‐ph‐3CzAnBzt). Using it as a host, the sky‐blue fluorescent OLED realizes the maximum EQE of 9.50%, and keeps as high as 9.27% and 8.56% at 1000 and 5000 cd m−2. More surprisingly, high‐performance hybrid white OLEDs (WOLEDs) with good color stability and low roll‐off are achieved by using it as the blue emitter. Two‐color WOLED shows the forward‐viewing efficiencies of 20.46%, and 76.80 lm W−1. The three‐color WOLED emitting a candlelight with the color rendering index of ≥ 82 realizes the maximum EQE of 21.49% and remains 20.80% at 1000 cd m−2. Such superior electroluminescence performance achieved in these OLEDs ranks among the highest values based on deep‐blue fluorophors with CIEy < 0.08. [ABSTRACT FROM AUTHOR]

It is well known that one of the major challenges facing white organic light‐emitting diodes (WOLEDs) has been to achieve high efficiency, low efficiency roll‐off, and high color rendering index (CRI) simultaneously. A simple charge‐ and exciton‐confining emitting layer structure formed by employing a blue emitting p/n heterojunction, and combined with red, yellow, and green phosphorescent ultrathin layers, is presented, thus realizing the stable utilization of 100% excitons. The resulting hybrid WOLEDs exhibit the maximum forward‐viewing external quantum efficiency and power efficiency of 23.4% and 50.4 lm W−1, and keep them at 20.3% and 31.2 lm W−1 at 1000 cd m−2, showing high efficiency and low efficiency roll‐off. Furthermore, the device also shows extremely stable electroluminescent spectra in the whole luminance range with a high CRI of 93 and the Commission Internationale de L'Eclairage coordinates of (0.49, 0.43) at 1000 cd m−2, which is perfect warm white for indoor lighting. The achievement of the excellent comprehensive performances is the best result reported to date among the conventional blue fluorescence‐based hybrid WOLEDs possessing such high CRI, which may be a new starting point for further research on high‐performance hybrid WOLEDs. [ABSTRACT FROM AUTHOR]