Decoupling the Roles of Mobility and Energy Level of Hole-Transport Layers to Efficiency Roll-Off in Perovskite Light-Emitting Diodes

Abstract

Metal halide perovskite light-emitting diodes (PeLEDs) have attracted significant attention due to their high efficiency, low cost, and solution processability. While the peak efficiency of PeLEDs has been significantly enhanced, severe efficiency roll-off remains a critical challenge for bright and stable devices. In this study, we investigate the impact of the hole transport layer (HTL) to the efficiency roll-off in PeLED based on FAPbI₃. Our findings reveal that the hole mobility of the HTL plays a crucial role in mitigating efficiency roll-off of the device, whereas the energy-level alignment primarily governs the peak efficiency. Furthermore, we implement an HTL with high hole mobility and proper energy-level alignment to promote charge carrier balance, thereby simultaneously realizing peak external quantum efficiency (EQE) enhancement and mitigating efficiency roll-off in FAPbI₃-based PeLEDs. Compared with near-infrared devices using the widely adopted low-mobility random copolymer HTL, our devices deliver a peak EQE of 21.7% at 84 mA cm^–2, retain over 10% EQE at 1300 mA cm^–2, and exhibit nearly 5-fold higher radiance. This study highlights the distinct roles of hole mobility and energy-level alignment in governing efficiency roll-off and peak device efficiency.