High-Performance Narrowband OLED with Low Efficiency Roll-Off Based on Sulfur-Incorporated Organoboron Emitter

Multi-resonance (MR) based organoboron emitters exhibiting high-efficiency narrowband thermally activated delayed fluorescence (TADF) have become a critical material component for constructing high-performance organic light-emitting diodes (OLEDs) with high color purity and high color gamut. However, most of the MR-TADF devices suffer from severe efficiency roll-off at high current density due to the relatively large singlet-triplet splitting energy, long excited state lifetime, and slow reverse intersystem crossing rate (k(RISC)). Herein, by utilizing a sulfur atom-fused donor unit, 7H-benzo[4,5]thieno[2,3-b]carbazole, an organic boron emitter (BTC-BNCz) capable of high efficiency and low efficiency roll-off narrowband TADF emission is developed. Benefitting from the heavy atom effect of the sulfur atom, k(RISC) up to 1.6 x 10(5) s(-1) is achieved, which could greatly reduce the undesired quenching effect. Consequently, the OLED using BTC-BNCz as dopant exhibits high external quantum efficiency (EQE) of 27.0% with full width at half maximum (FWHM) of 35 nm. Moreover, by utilizing a TADF material with a high horizontal dipole ratio as assistant host, outstanding device performance is achieved with a maximum EQE of 35.2% and FWHM of 37 nm, featuring slow efficiency roll-off.