# Decrystallization of CH3NH3PbI3 perovskite crystals via polarity dependent localized charges

## TL;DR

This study reveals how the polarity of localized charges influences the degradation pathways of CH3NH3PbI3 perovskite crystals, showing that hole-rich and electron-rich films degrade differently depending on environmental gases, with insights supported by experiments and simulations.

## Contribution

It uncovers the polarity-dependent degradation mechanisms of perovskite crystals through combined experimental and ab initio molecular dynamics analyses.

## Key findings

- Hole-rich films degrade faster with water presence.
- Electron-rich films are more stable in humid air.
- Degradation pathways are confirmed by spectroscopic measurements.

## Abstract

Despite soaring performance of organic-inorganic hybrid perovskite materials in recent years, the mechanism of their decomposition at actual operation condition has been elusive. Herein, we elucidated the decrystallization process of CH3NH3PbI3 perovskite crystals via localized charges and identified polarity-dependent degradation pathway by carrying out time-evolution measurements for absorption spectra of perovskite films with underlying different charge transport layers and ab initio molecular dynamics calculations. It was found that the carrier polarity (hole-rich or electron-rich) inside the perovskite films played a critical role in the degradation rate, and polarity-dependent degradation pathway strongly depended on the combination of surrounding gaseous molecules. The hole-rich perovskite films degraded more rapidly in the existence of H2O than the electron-rich one, while the degradation trend became opposite in only-oxygen ambient. Strikingly, the hole-rich one was extremely weak to atmospheric air containing both H2O and O2, whereas the MAPbI3 film with excessive electrons rather stabilized in air. Ab initio molecular dynamics (AIMD) simulation was also done to find the detailed degradation pathway of MAPbI3 under atmosphere for different polarity of localized charge, which are in good agreement with experimental results. Furthermore, X-ray assisted spectroscopic measurements confirmed the production of Pb(OH)I as predicted from the simulation result.

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Source: https://tomesphere.com/paper/1812.01931