Atomistic and Electronic Origin of Phase Instability of Metal Halide Perovskites

Abstract

The excellent optoelectronic properties of metal halide perovskites (MHPs) have attracted extensive scientific interest and boosted their application in optoelectronic devices. Despite their attractive optoelectronic properties, their poor stability under ambient conditions remains the major challenge, hindering their large-scale practical applications. In particular, some MHPs undergo spontaneous phase transitions from perovskites to nonperovskites. Compositional engineering via mixing cations or anions has been widely reported to be effective in suppressing such unwanted phase transitions. However, the atomistic and electronic origins of the stabilization effect remain unexplored. Here, by using density functional theory calculations, we provide insights for the undesired phase transition of pristine perovskites (FAPbI3, CsPbI3, and CsSnI3) and reveal the mechanisms of the improved phase stability of the mixed compounds [Cs x FA1–x PbI3, CsSn y Pb1–y I3, and CsSn­(Br z I1–z )3]. We identify that the phase transition is correlated with the relative strength of the M–X bonds as well as that of the hydrogen bonds (for hybrid compositions) in perovskite and nonperovskite phases. The phase transition can be suppressed by mixing ions, giving rise to either an increased bond strength for the perovskite or a decreased bond strength in their nonperovskite counterparts, or suppressed vacancy defect formation for Sn–Pb mixed perovskites. Our results present a comprehensive understanding of the mechanisms for the phase instability of MHPs and provide design rules for engineering phase-stable perovskite compositions.

Temperature dependency of excitonic effective mass and charge carrier conduction mechanism in CH3NH3PbI3−xClx thin films

“…Such phase transition can modify the physical properties of mixed halide perovskites, though it does not cause remarkable change in optical and photovoltaic properties 43 . Recently, tetragonal to cubic phase transition is associated with the relative strength of the metal-halogen and hydrogen bonds as reported 44 . In our study, during the temperature dependent Hall measurement we have applied a magnetic field of ~ 1 T. This magnetic energy shifted the tetragonal to cubic phase transition at slightly higher temperature at (340–344) K.…”

A Reparameterized Density Functional Tight-Binding Method for Engineering phase-stable CsPbX\textsubscript{3} Perovskites

“…Computational modelling has proven to be a valuable complement to experimental studies, allowing for atomic scale insights that are otherwise difficult to obtain. [19][20][21] Most computational studies of MHPs are performed using density functional theory (DFT). [22][23][24] However, due the high computational costs of DFT it is unsuitable for the simulation of large systems over long timescales.…”

The role of sodium in stabilizing tin–lead (Sn–Pb) alloyed perovskite quantum dots

“…5,[14][15][16][17][18] Additionally, mixing Sn and Pb is beneficial for stabilizing the fragile Sn-perovskite cubic phase and retarding the oxidation of Sn 2+ to Sn 4+ . 14,[19][20][21][22][23] As a result, the alloyed Sn-Pb perovskite solar cells already showed enhanced phase stability and improved power conversion efficiency, making them attractive for various optoelectronic applications. [24][25][26][27] Reducing crystallite size to the nanometer scale, for example, quantum dot (QD) dimension, further improves their phase stability because of the large contribution of surface energy and the protection by organic passivation ligands.…”