Strategies for Enhancing Efficiency and Operational Stability in Green Phosphorescence-Sensitized Fluorescence (PSF) Organic Light-Emitting Diode (OLED) Technology.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have gained considerable attention to solve the color purity issue in organic light-emitting diode (OLED) commercialization. However, their slow reverse intersystem crossing rate (kRISC) leads to the severe efficiency roll-off and reduced operational stability. To address this limitation, phosphorescence-sensitized fluorescence (PSF) technology has been widely adopted. Nevertheless, the external quantum efficiency (EQE) of PSF OLED is relatively low compared to TADF-sensitized fluorescence (TSF) OLED, where the relatively low radiative rate (kr) (∼105 - 106 s-1) of phosphorescence sensitizer (PS) limits the Forster resonance energy transfer (FRET) rate and exciton utilization in PSF OLEDs. This review, describes the techniques to improve the FRET rate by optimizing the physical parameters related to it. From the analysis, the FRET rate of the PSF OLEDs can be enhanced by improving the terminal emitters' (TE's) extinction coefficient (ε) and a large spectral overlap (J) with PS emission. Further, utilizing the dual-channel energy transfer process, combined with high T1 exciplex host system to suppress the back energy transfer (BET) from PS to the host, resulting in high EQE. Furthermore, the stability of the PSF OLED can be improved by the utilization of a highly stable intrinsic ET-type host, and TE materials.