Halide ion migration in lead-free all-inorganic cesium tin perovskites

Abstract

Halide perovskites have been one of the most promising research hotspots in the optoelectronic field. Recently, the issue of ion migration has been proved to be of great significance to their long-term stability and performance of optoelectronic devices. However, the stability of perovskite Cs2SnX6 (X = I, Br, Cl) under the light or electric field conditions has not been explored. In this work, we reported halide ion migration in lead-free all-inorganic perovskite Cs2SnX6. The calculated formation energy to some degree reveals the concentration of the halide vacancy, which provides the favorable conditions for halide ion migration. Importantly, the theoretical long-term ion migration barriers are investigated to be higher than 1.00 eV, indicating they are relatively stable compared to CsPbX3, and the computational result matches the experimental result with the Nernst-Einstein relation that we adopted. The halogen ion migration energy barrier is 0.91 eV under the bias of 5 V, indicating that the perovskite Cs2SnX6 is relatively stable under a certain electric field. Furthermore, the experimental comparison of XRD results demonstrate that perovskite Cs2SnX6 has no obvious ion migration under certain light conditions. Finally, the analysis results show the Sn-X bond strength that explains the cause of such high barriers. These results reveal the migration mechanism of halide ions and provide new impetus for their optoelectronic applications.