Asymmetrical‐Dendronized TADF Emitters for Efficient Non‐doped Solution‐Processed OLEDs by Eliminating Degenerate Excited States and Creating Solely Thermal Equilibrium Routes

Autor: Chensen Li, Alastair K. Harrison, Yuchao Liu, Zhennan Zhao, Cheng Zeng, Fernando B. Dias, Zhongjie Ren, Shouke Yan, Martin R. Bryce
Rok vydání: 2022
Předmět:
Zdroj: Angewandte Chemie International Edition, 2022, Vol.61(19), pp.e202115140 [Peer Reviewed Journal]
ISSN: 1521-3757
0044-8249
Popis: Two asymmetric “half-dendronized” and “half-dendronized-half-encapsulated” TADF emitters eliminate degenerate excited states, assuring a solely thermal equilibrium route for an effective spin-flip process. AEE properties can minimize the exciton quenching. The isolated encapsulating tricarbazole unit protects the TADF unit, reducing nonradiative decay. Non-doped OLEDs with a remarkably high EQEmax of 24.0 % and low roll-off are achieved. The mechanism of thermally activated delayed fluorescence (TADF) in dendrimers is not clear. We report that fully-conjugated or fully-nonconjugated structures cause unwanted degenerate excited states due to multiple identical dendrons, which limit their TADF efficiency. We have synthesized asymmetrical “half-dendronized” and “half-dendronized-half-encapsulated” emitters. By eliminating degenerate excited states, the triplet locally excited state is ≥0.3 eV above the lowest triplet charge-transfer state, assuring a solely thermal equilibrium route for an effective spin-flip process. The isolated encapsulating tricarbazole unit can protect the TADF unit, reducing nonradiative decay and enhancing TADF performance. Non-doped solution-processed devices reach a high external quantum efficiency (EQEmax) of 24.0 % (65.9 cd A−1, 59.2 lm W−1) with CIE coordinates of (0.24, 0.45) with a low efficiency roll-off and EQEs of 23.6 % and 21.3 % at 100 and 500 cd m−2.
Databáze: OpenAIRE
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