Selection of compatible blended cohost towards boosting performance of TADF-polymer light-emitting electrochemical cells

Abstract

Light-emitting electrochemical cells (LECs) using thermally activated delayed fluorescent (TADF) polymer emitter are attractive since they own the great potential in fabricating robust LECs with low-cost and high efficiencies towards various applications. However, current scarce study disclosed that it is hard to simultaneous optimize electrochemical doping and multi-component miscibility of the emissive layer, which renders luminance and external quantum efficiency (EQE) of TADF-polymer LECs still quite low, e.g. less than 500 cd m⁻² and 1.0 %. Here, we propose to select compatible p-type and n-type small molecules as cohost of TADF-polymer emitter, which is critical to simultaneously achieve balanced, efficient p-/n-type electrochemical doping and charge transport, efficient energy transfer from cohost to TADF-polymer emitter and most importantly well restrained intra- and inter-molecular interactions, i.e. self-aggregation of host and redshift effect of host on TADF-polymer emitter. TADF-polymer LEC using such a qualified compatible cohost achieved a peak luminance of 1292 cd m⁻², a peak EQE of 2.24 %, and a peak luminous efficiency of 6.89 cd A⁻¹ at 6.5 V, which is distinctly superior to that of control devices and earlier report of TADF-polymer LECs. It proves the effectiveness of such strategy and provides a research thought on further developments.