In situ probing of phase transition kinetics of single CsPbI3 perovskite quantum dots via nano-impact electrochemistry.

Purification using polar solvents such as ethyl acetate (EtOAc) inevitably triggers a γ-to-δ phase transition in perovskite quantum dots (QDs), thereby deteriorating their structural integrity and optoelectronic performance. Understanding the intrinsic kinetics of this phase transition at the single-particle level remains a big challenge. Herein, we report an in situ electrochemical strategy based on nano-impact electrochemistry to probe the phase transition kinetics of CsPbI3 QDs in EtOAc at the single-nanoparticle level. By exploiting the distinct Pb reduction overpotentials of γ- and δ-phase CsPbI3, the γ-phase fraction of single QDs during solvent exposure was quantified in real time through statistical analysis of current spikes generated as individual QDs collided with a microelectrode. Kinetic modeling using the Johnson-Mehl-Avrami-Kolmogorov framework suggests that the γ-to-δ phase transition proceeds via heterogeneous nucleation followed by low-dimensional interfacial propagation under strong nanoscale confinement. Compared with ensemble-averaged ex situ XRD measurements, the nano-impact approach enables more accurate and precise kinetic fitting and improved mechanistic resolution of the phase-transition process. This work demonstrates that nano-impact electrochemistry enables in situ monitoring of phase transition kinetics at the single-particle level, revealing solvent-induced structural evolution and guiding the design of more robust purification strategies to stabilize perovskite QDs.