emitters exhibit good color purity with small full width at half maximum (FWHM) of electroluminescent spectra, which promises next-generation ultrahighdefinition display. Up to now, most of the high-performance MR-TADF OLEDs were fabricated by vacuum deposition, [7] which requires expensive equipment and excessive energy consumption. Solutionprocessing methods have special advantages, such as large-area and low-cost manufacturing, which is a more economical approach for the mass production of OLED displays. [24][25][26][27][28][29][30][31][32][33] However, the device performance of solution-processed MR-TADF OLEDs remains far away from that of their vacuum-deposited counterparts. Especially, the efficiency roll-off at high luminance is very large, [6,10,20,[34][35][36][37] which hinders its practical application.The MR-TADF emitters usually have a moderate singlet-triplet energy splitting (ΔE ST ), [1,11,[19][20][21][22] which results in slow reverse intersystem crossing (RISC) process. So, the conversion of triplet excitons to singlet ones on MR-TADF emitters is inefficient. And the large number of unconverted triplet excitons would accumulate at the light-emitting layer (EML) to induce triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA). The triplet exciton annihilation becomes even more serious at practical luminance with high exciton density, which leads to large efficiency roll-off. [38,39] This problem could be solved by codoping a thermally activated delayed fluorescent (TADF) material with high RISC rate in the EML as the sensitizer for the MR-TADF emitters. [15] The triplet excitons could be converted to singlet ones rapidly on the sensitizer, and then transfer to the MR-TADF emitter through long-range Förster resonance energy transfer (FRET) for narrowband emission. [17] With this approach, a lot of high-performance vacuumdeposited MR-TADF OLEDs have been reported by developing efficient TADF sensitizers. [40][41][42][43][44][45][46][47][48] However, this approach has not successfully achieved promising device performance in solution-processed MR-TADF OLEDs, due to the lack of solutionprocessible TADF sensitizers with high RISC rate. [37] Solution-processed organic light-emitting diodes (OLEDs) based on multipleresonance thermally activated delayed fluorescence (MR-TADF) emitters exhibit high color purity for next-generation ultrahigh-definition display. However, they suffer from low efficiency and large efficiency roll-off due to slow triplet exciton upconversion of MR-TADF emitters, resulting in serious triplet exciton quenching. Here, efficient solution-processed blue MR-TADF OLEDs featured with small efficiency roll-off are developed by using a new bulky TADF sensitizer consisting of five di-tert-butylcarbazoles and one triazine with high reverse intersystem crossing rate of 2.0 × 10 7 s −1 , which can rapidly convert triplet excitons to singlet ones to avoid exciton quenching. The Dexter energy transfer from the sensitizer to the MR-TADF emitter is blocked by using tertiary b...

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Solution-processed white organic light-emitting diodes (WOLEDs) have shown much lower device efficiency than vacuum-deposited counterparts, due to the lack of triplet exciton management in single-emissive-layer device structure, which will induce...

Two kinds of polystyrene‐based through‐space charge transfer (TSCT) polymers consisting of spatially‐separated acridan donor moieties bearing phenyl or naphthyl substituents and triazine acceptor moieties are designed and synthesized. It is found that TSCT polymers containing phenyl‐substituted acridan donors exhibit high‐lying singlet (S1) and triplet (T1) states with small singlet‐triplet energy splitting (∆EST) of 0.04–0.05 eV, resulting in thermally activated delayed fluorescence (TADF) with reverse intersystem crossing rate constants of 1.1–1.2 × 106 s−1. In contrast, polymers bearing naphthyl‐substituted acridan donors, although still having TSCT emission, exhibit no TADF effect because of the large ∆EST of 0.30–0.33 eV induced by low‐lying locally excited T1 state of naphthyl donor moiety. Solution‐processed organic light‐emitting diodes using TSCT polymers containing phenyl‐substituted acridan donors reveal sky‐blue emission at 483 nm together with maximum external quantum efficiency (EQE) of 11.3%, which is about 30 times that of naphthyl‐substituted counterpart with maximum EQE of 0.38%, shedding light on the importance of high triplet energy level of donor moiety on realizing TADF effect and high device efficiency for through‐space charge transfer polymer.

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