Antiphase boundary in CH$_3$NH$_3$PbI$_3$ repels charge carriers while promotes fast ion migrations

TL;DR

This study visualizes and characterizes antiphase boundaries in CH3NH3PbI3 perovskites, revealing their dual role in repelling charge carriers and facilitating ion migration, which impacts stability and optoelectronic performance.

Contribution

The paper provides atomic-scale visualization of APBs in CH3NH3PbI3 and links their structure to electrical, ionic activities, and stability, offering new insights for improving perovskite solar cells.

Findings

APBs are caused by half-unit-cell shifts in the octahedral framework.

APBs repel electrons and holes, affecting charge transport.

APBs serve as fast ion migration channels, leading to decomposition.

Abstract

Defects in organic-inorganic hybrid perovskites (OIHPs) greatly influence their optoelectronic properties. Identification and better understanding of defects existing in OIHPs is an essential step towards fabricating high-performance perovskite solar cells. However, direct visualizing the defects is still a challenge for OIHPs due to their sensitivity during electron microscopy characterizations. Here, by using low dose scanning transmission electron microscopy techniques, we observe the common existence of antiphase boundary (APB) in CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$), resolve its atomic structure, and correlate it to the electrical/ionic activities and structural instabilities. Such an APB is caused by the half-unit-cell shift of [PbI$_6$]$_4$-octahedron along the [100]/[010] direction, leading to the transformation from corner-sharing [PbI$_6$]$_4$-octahedron in bulk MAPbI$_3$ into edge-sharing ones at the APB. Based on the identified atomic-scale configuration, we further carry out density functional theory calculations and reveal that the APB in MAPbI$_3$ repels both electrons and holes while serves as a fast ion-migration channel, causing a rapid decomposition into PbI$_2$ that is detrimental to optoelectronic performance. These findings provide valuable insights into the relationships between structures and optoelectronic properties of OIHPs and suggest that controlling the APB is essential for their stability.