Synergistic Mitigation of Phase Segregation and Blinking Suppression Along with Enhanced Electrocatalytic Activity in CsPbBrI ₂ Perovskite Nanocrystals via Ascorbic Acid Surface Treatment

Abstract Mixed‐halide CsPbBrI ₂ perovskite nanocrystals (PNC) exhibit defect tolerance and a low bandgap, making them promising for optoelectronic, photovoltaic, and catalytic applications. However, their performance is hindered by phase instability under light exposure and electrical bias, driven by iodine expulsion, which disrupts charge transport and is further exacerbated by trap‐mediated intense photoluminescence (PL) blinking. This study investigates the nature of these trap states and their role in carrier recombination through ensemble‐ and single‐particle‐level analyses. These findings highlight the critical role of passivating ligands in stabilizing PNCs, identifying ascorbic acid (AA) as an optimal surface passivation due to its multidentate binding capability, as further supported by DFT calculations. Trion blinking in untreated PNCs indicates the presence of long‐lived trap states, whereas AA‐treated PNCs, which retain only shallow traps near the band edges, exhibit exclusively band‐edge carrier (BC) blinking. AA‐treated PNCs double the ON fraction in PL trajectories and remain stable for over 90 days in ambient conditions. By effectively passivating deep traps, AA treatment suppresses charge carrier trapping, mitigates phase segregation, and enhances charge transport. Leveraging these improvements, AA‐treated CsPbBrI ₂ PNCs are employed for the first time as electro/photoelectro‐catalysts in the reduction of 4‐nitrophenol, exhibiting exceptional performance.