Controlling Electronic-Ionic Kinetics via Size Engineering in CsPbBr₃ Perovskite Nanocrystals

Owing to the exceptional photovoltaic and optoelectronic properties of metal halide perovskites, they have sparked an intensive interest in the research community. CsPbBr₃ perovskite nanocrystals (NCs) have come into sight due to their versatile properties that can be achieved through structural modification. While the prior research on perovskite nanocrystals has focused mainly on tuning optical and electronic properties, the understanding of their electronic-ionic kinetics still remains a significant research gap. In this work, we explore how the size of CsPbBr₃ NCs impacts their electronic-ionic properties by using electrochemical impedance spectroscopy (EIS). We systematically tune NC size and investigate the resulting dielectric properties, conductivity, and capacitance. Notably, larger NCs exhibit anomalous behavior similar to that of perovskite polycrystalline thin films in the range of 0.4-0.6 V, indicating strong electronic-ionic coupling. Conversely, smaller NCs display weak electronic-ionic coupling due to ion localization. Additionally, this study sheds light on the electronic-ionic behavior of NCs approaching quantum confinement with a size reduction, suggesting opportunities for defect engineering. Ultimately, this work will pave the way for developing advanced electronic devices utilizing perovskite nanocrystals.