Ideal blue thermally activated delayed fluorescence emission assisted by a thermally activated delayed fluorescence assistant dopant through a fast reverse intersystem crossing mediated cascade energy transfer process

Abstract

A novel blue thermally activated delayed fluorescence (TADF) organic light-emitting diode with an emitting layer made up of a TADF assistant dopant and a pure blue-emitting TADF emitter was developed to demonstrate a pure blue color, a high external quantum efficiency, suppressed efficiency roll-off, and an improved lifetime. Two fused B–N type blue TADF emitters with a narrow emission spectrum were used as the blue emitters and the narrow blue emission was harvested by a TADF assistant dopant through a reverse intersystem crossing mediated cascade energy transfer process. A high external quantum efficiency of 31.4%, pure blue emission color of (0.13, 0.15), significant reduction of the efficiency roll-off and more than 10 times lifetime extension were simultaneously achieved using the TADF assisted TADF process.