Ion Migration in Lead-Halide Perovskites: Insights from First-Principles Calculations

Lead-halide perovskites (LHPs) are promising semiconductors especially for efficient solar cells. However, LHP cells show hysteresis in the current-voltage curves and their stability with respect to water exposure is problematic. These issues are possibly related to defect migration occurring in the perovskite material [1]. Here, we present our first-principles results on defect migration phenomena in hybrid and all-inorganic LHPs.[2,3] Our calculations are based on density functional theory and nudged-elastic band methods to optimize minimum energy pathways of defect species. First, the migration of hydrogen interstitials is discussed,[1] where we find that migration barriers are small, indicating mobile hydrogen interstitials at room temperature. Second, results on migration and anion-exchange reactions of interstitial Cl in all-inorganic CsPbI$_3$ are presented.[2] Cl migration is found to facilitate Cl doping at levels near the solubility limit for chloride in CsPbI$_3$. At these incorporation levels the stability of a CsPbI$_3$ film is strongly improved compared to an undoped film. References: [1] Egger et al., Acc. Chem. Res. 49, 573 (2016), and references therein. [2] Egger et al., Angew. Chem. Int. Ed. 54, 12437 (2015). [3] Dastidar et al., Nano Lett. 16, 3563 (2016).