Device engineering for high-performance OLEDs based on 4CzPN thermally activated delayed fluorescent emitter

Abstract

The electroluminescent performance and luminescent dynamics of devices are explored in depth via doping and host engineering, where thermally activated delayed fluorescent (TADF) material 3,4,5,6-tetrakis(carbazol-9-yl)-1,2-dicyanobenzene (4CzPN) serves as the emitter. The evolution of the exciton recombination zone with different hosts is discussed. In the case of TCTA host, the recombination zone is situated near the EML/ETL interface, resulting in the formation of various excitons, including monomer exciton, electroplex as well as electromer. The competition among these radiative pathways detrimentally affects the device performance and should be circumvented in the design of device structures. The mCP-hosted device provides the best performance with the highest efficiencies of 31.3 cd/A, 15.8 lm/W and 9.13 % due to its efficient energy transfer and balanced charge carrier mobilities. This study emphasizes that device engineering is an effective strategy for manipulating exciton recombination region and energy transfer, thus promoting the development of high performance TADF-based OLEDs.