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.