Solution‐Processable Thermally Activated Delayed Fluorescence White OLEDs Based on Dual‐Emission Polymers with Tunable Emission Colors and Aggregation‐Enhanced Emission Properties
Chensen Li, Roberto S. Nobuyasu, Yukun Wang, Fernando B. Dias, Zhongjie Ren, Martin R. Bryce, Shouke Yan
Abstract : Thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) have drawn tremendous interest and have been extensively studied because of harvesting both triplet and singlet excitons without heavy metals. However, single white-light-emitting polymers are currently limited and few strategies exist to design these materials. Herein, a new strategy is proposed to develop the polymers with tunable emission colors by combining fluorescence and TADF based on aggregation-enhanced emission (AEE) characteristics. The polymers containing different ratios of pendant 2-(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide units with yellow TADF emission and dibenzothiophene units with blue fluorophor emission, which display both TADF and AEE characteristics, are synthesized successfully. Among them, the emission color of P3 in different tetrahydrofuran/water mixtures changes from greenish-blue to white or yellow. Moreover, P3 displays white emission in the solid state dispersing by poly(methyl methacrylate). In addition, electroluminescent device of P3 achieve white light emission with high color rending indexes (CRI) and low turn-on voltages (V on ). P3 OLEDs show two-color warm-white emission with high CRI of 77, low V on of 2.9 V, CEmax of 23.0 cd A−1, PEmax of 32.8 lm W−1, external quantum efficiency (EQE)max of 10.4% with Commission Internationale de l'Eclairage coordinates of (0.37, 0.38) at 5 V. Moreover, EQE of 2.6%, CE of 5.7 cd/A, PE of 4.7 lm W−1 at 100 cd m−2 are obtained. To the best of our knowledge, this work reports the first example of warm-white TADF polymer OLEDs.
