H2S-induced surface reconstruction enables efficient CsPbI3 QLEDs with ultralow roll-off.

Metal halide perovskite quantum dots (QDs) are promising materials for developing low-cost and high-performance quantum dot-based light-emitting diodes (QLEDs). Despite external quantum efficiency (EQE) comparable to II-VI/III-V QLEDs, perovskite QD counterparts achieve peak EQE at low luminance/current density and exhibit significantly more pronounced efficiency roll-off, owing primarily to their ionic character and soft lattice. Engineering a robust surface is essential to ensure the structural stability of perovskite QDs, yet achieving this remains a critical challenge. Here, we develop an H2S-mediated surface passivation strategy. Experimental measurements confirm Pb-S coordination and a reduction in oleylamine ligand density, while DFT calculations suggest that (H2S)2 dimers may additionally interact with Cs-vacancy-related surface environments. This H2S-induced surface reconstruction creates a more robust surface coordination environment in CsPbI3 QDs. Benefiting from the enhanced surface stability, LEDs incorporating the treated CsPbI3 QDs possess increased ion migration barrier, balanced charge injection, and suppressed Auger recombination. These combined improvements yield a peak EQE of 30.71% at 52 mA cm-2 and 91.46 W Sr-1 m-2, with the device maintaining EQEs of 18.59% at ~500 mA cm-2 and 21.15% at ~500 W Sr-1 m-2, as well as an operational half-lifetime of 104,587 h.