To improve the efficiency of thermally activated delayed fluorescence OLEDs by controlling the horizontal orientation through optimizing stereoscopic and linear structures of indolocarbazole isomers

Abstract

Molecular structures play a critical role in forming the horizontal orientation of the emission transition dipole of light-emitting TADF materials which can improve the light outcoupling efficiency of OLEDs. Here, two TADF emitters of IndCzpTr-1 and IndCzpTr-2 based indolocarbazole derivatives with stereoscopic and linear structures were designed and synthesized. With a smaller ΔE_ST, better thermal stability and preferential horizontal orientation with an orientation order parameter S of −0.264, a green TADF OLED device based on IndCzpTr-2 realized a maximum EQE of 30.0% and maximum current efficiency (CE) of 82.6 cd A⁻¹ without using any optical outcoupling technology; meanwhile, a sky-blue TADF OLED with a maximum EQE of 14.5% and a maximum CE of 28.1 cd A⁻¹ was obtained for IndCzpTr-1 with a homologous device structure.