Ab initio study of the dynamics of electron trapping and detrapping processes in the CH3NH3PbI3 perovskite

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)2135-2147
Journal / PublicationJournal of Materials Chemistry A
Volume7
Issue number5
Online published24 Dec 2018
Publication statusPublished - 7 Feb 2019

Abstract

Charge trapping and detrapping are responsible for a number of unusual properties in the CH3NH3PbI3 (MAPbI3) perovskite such as photoinduced ion migration, photodegradation, and current density-voltage hysteresis. However, little is known about the dynamic processes of charge trapping and detrapping at the trap sites. Herein, the behavior of excess electron trapping and its interplay with iodine vacancies in the MAI-terminated and PbI2-terminated MAPbI3 surfaces were studied using density functional theory (DFT) calculations. The results show that the positively charged iodine vacancy (V1 +) is energetically more favorable to stay at the top-surface layer. By trapping excess electrons, the iodine vacancy migrates from the top-surface layer to the subsurface layer due to the formation of deep-level trap states. On the other hand, the adsorption of OH radicals and O2 molecules induces electron detrapping from the deep-level trap states and iodine vacancies migration from the subsurface back to the top-surface layer. Furthermore, we studied the electron trapping and detrapping processes in bulk MAPbI3. We found that in bulk MAPbI3, the excess electrons facilitate the clustering of the iodine vacancies together and form deep trap states via the iodine migration process. However, electron detrapping was found to induce the hopping of two adjacent iodine vacancies away from each other. Our results show that while excess electrons trapped in both the shallow-level and deep-level states enhance the photodegradation of MAPbI3 under humid air conditions, the electrons in the deep-level traps play a significantly more important role in facilitating photoinduced ion migration and the hysteresis behavior.