Investigation of the Role of Cations during Anion Exchange in All-Inorganic Halide Perovskite Nanocrystals

All-inorganic lead halide perovskite nanocrystals (PeNCs) exhibit tunable optical bandgap energies by adjusting their compositions. PeNC-based optical or optoelectronic devices have been developed using the anion exchange strategy, which can replace the X-site anion with the target halide without phase transition. Thus, various methods for adjusting the anions in PeNCs have been developed; however, the cation effect on anion exchange has rarely been discussed. Here, we investigated the effect of cations on the optical bandgap energy and stability of CsPbX3 (X = Cl, Br, and I) PeNCs by analyzing as cation candidates NH4+, Na+, K+, and TBA+. Among them, NH4Cl and NaI are efficient anion-exchanging chemicals because they effectively provide Cl− or I−, respectively, to PeNCs without structural deformation. The halide sources allow exchange in the composition of PeNCs under benign conditions, such as atmospheric conditions and 298 K. This phenomenon is explained using the hard-soft acid-base (HSAB) theory. We believe that these findings will contribute to the improvement of optoelectronic devices, such as solar cells, displays, and light-emitting diodes (LEDs).