High Spectral Resemblance Index Candlelight Organic Light-Emitting Diodes Based on Cascade Energy Transfer

Candlelight organic light-emitting diodes (OLEDs) are promising for bio-friendly lighting due to their low blue-light emission. However, there is still a significant challenge for highly efficient candlelight OLEDs to achieve both a high spectral resemblance index (SRI) and a simplified architecture. In this work, we propose a cascade energy transfer strategy by incorporating a novel interfacial exciplex with double reverse intersystem crossing (RISC) channels and a thermally activated delayed fluorescence (TADF) emitter to construct a multi-RISC system, which can regulate exciton behaviors and achieve multi-emission synergy between a TADF emitter and a phosphorescent emitter. As a result, the simplified device achieves a single-peak record-high SRI of 93.43% with a maximum power efficiency of 47.42 lm/W, representing one of the best performances to date. Moreover, a low blue light hazard efficiency of 2.16×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> W/lm at 9 V and a melatonin suppression sensitivity of 3.69% at 100 cd/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are achieved. These results open new avenues for developing a health light source with negligible blue light hazard.