Recoverable Defect Suppression in CsPbI₃ Quantum Dots for Efficient and Stable Pure-Red Light-Emitting Diodes

Pure-red light-emitting diodes (LEDs) based on CsPbI₃ quantum dots (QDs) have garnered considerable attention owing to their stable emission spectra and efficient electroluminescence. However, their operational stability presently lags far behind that of state-of-the-art perovskite LEDs. Here, we employ photoactive phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (PPO) molecules to resurface small-sized CsPbI₃ QDs. The combination of sterically hindered PPO and small-sized methylacrylic acid (MA) ligands can comprehensively reduce uncoordinated Pb²⁺ on QD surfaces, which are related to nonradiative recombination. Moreover, the optimized QD films exhibit enhanced conductivity, showing more than 3.3-fold improvements over control QDs. Consequently, we demonstrate pure-red QD-based light-emitting diodes (QLEDs) with a maximum external quantum efficiency of up to 31.5% as well as a maximum luminance of 2434 cd m^-2. More importantly, the photoactive PPO molecules release trimethylbenzoyl radicals under ultraviolet irradiation to further passivate newly generated defects in perovskites under operational conditions, thereby enabling the recovery of performance in aged devices. Based on this, we present QLEDs with an excellent operational stability (half-lifetime) of up to 300 h, representing one of the most stable pure-red perovskite QLED reported to date.