Efficient and Bright Blue Thermally Activated Delayed Fluorescence from Light‐Emitting Electrochemical Cells

Abstract

AbstractLight‐emitting electrochemical cells (LECs) comprising metal‐free molecules that emit by the process of thermally activated delayed fluorescence (TADF) can be both sustainable and low cost. However, the blue emission performance of current TADF‐LECs is unfortunately poor, which effectively prohibits their utilization in important applications, such as illumination and full‐color displays. Here, this drawback is addressed through the development of a TADF‐LEC, which delivers blue light emission (peak wavelength = 475 nm) with a high external quantum efficiency of 5.0%, corresponding to a current efficacy of 9.6 cd A‐1. It is notable that this high efficiency is attained at bright luminance of 740 cd m‐2, and that the device turn‐on is very fast. It is demonstrated that this accomplishment is enabled by the blending of a carbazole‐based 9‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)‐2‐methylphenyl)‐3,6‐dimethyl‐9H‐carbazole guest emitter with a compatible carbazole‐based tris(4‐carbazoyl‐9‐ylphenyl)amine:2,6‐bis(3‐(carbazol‐9‐yl)phenyl)pyridine blend‐host for the attainment of bipolar electrochemical doping, balanced electron/hole transport, and exciplex‐effectuated host‐to‐guest energy transfer.