Triazatruxene based star-shaped thermally activated delayed fluorescence emitters: modulating the performance of solution-processed non-doped OLEDs via side-group engineering

Abstract

High performance solution processable thermally activated delayed fluorescence (TADF) emitters are of huge importance in the development of organic light-emitting diodes (OLEDs). In this article, two solution processable D₃–A star-shaped TADF emitters, namely TATC-TRZ and TATP-TRZ, with different flexible alkyl and rigid phenyl side chains are developed. Both emitters show similar photophysical properties and obvious TADF characteristics with a sub-micro second delayed lifetime of 0.6 μs for TATC-TRZ and 0.4 μs for TATP-TRZ while the flexible alkyl chain ensures TATC-TRZ with superior film forming ability and morphological stability compared to TATP-TRZ. Owing to such advantages, solution processed non-doped OLEDs based on TATC-TRZ secure a high maximum external quantum efficiency (EQE_max) of 7.5% and current efficiency (CE_max) of 19.9 cd A⁻¹, respectively, which is much higher than that of TATP-TRZ with EQE_max of 2.8% and CE_max of 7.4 cd A⁻¹. This work demonstrates the effectiveness of a flexible alkyl tail on the performance of solution-processed devices.