Affiliation:
1. Institute of Polymer Optoelectronic Materials and Devices Guangdong Provincial Key Laboratory of Luminescence from Molecular Aggregates Guangdong‐Hong Kong‐Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials State Key Laboratory of Luminescent Materials and Devices South China University of Technology Guangzhou 510640 China
2. Shenzhen Institute of Molecular Aggregate Science and Engineering School of Science and Engineering The Chinese University of Hong Kong Shenzhen, 2001 Longxiang Boulevard, Longgang District Shenzhen City Guangdong 518172 China
Abstract
Abstract“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.
Funder
National Natural Science Foundation of China
Subject
Atomic and Molecular Physics, and Optics,Electronic, Optical and Magnetic Materials