C1-substituted bipolar spiro host for high-performance organic light-emitting diodes

Abstract

High-performance organic light-emitting diodes (OLEDs) are essential for both academic research and industrial applications. Despite significant advancements in emitter design, the development of suitable host materials remains a critical challenge. In this study, we designed and synthesized a bipolar host material, STFPPO, by incorporating triphenylphosphine oxide into the C1 position of the 10-phenyl-10H-spiro[acridine-9,9′-fluorene] (STF) skeleton. In line with expectations, STFPPO exhibited a high triplet state energy level along with excellent thermal and morphological stability. When used as a host for the emitter iridium(III) bis(4,6-(difluorophenyl)-pyridinato-N,C′)picolinate (FIrpic), STFPPO achieved a maximum external quantum efficiency (EQE_max) of 24.3%. Furthermore, employing STFPPO as the host for the classical multi-resonance thermally activated delayed fluorescence (MR-TADF) material BNCz resulted in an EQE_max of 33.3%. All fabricated devices demonstrated minimal efficiency roll-off and low driving voltages, confirming the effectiveness of STFPPO as a superior host material for OLEDs.