Atomic-scale imaging of CH3NH3PbI3 structure and its decomposition pathway

TL;DR

This study uses advanced electron microscopy to reveal the atomic structure and decomposition pathway of CH3NH3PbI3 perovskite, identifying intermediate phases and bond destruction mechanisms crucial for improving stability.

Contribution

It introduces a low-dose imaging technique to observe atomic-scale structure and decomposition pathways of MAPbI3, including the identification of an intermediate phase and bond-breaking processes.

Findings

Imaged atomic structure of MAPbI3 in real space.

Discovered a two-step decomposition process with an intermediate phase.

Observed bandgap increase from ~1.6 eV to ~2.1 eV during degradation.

Abstract

Understanding the atomic structure and structural instability of organic-inorganic hybrid perovskites is the key to appreciate their remarkable photoelectric properties and failure mechanism. Here, using low-dose imaging technique by direct-detection electron-counting camera in transmission electron microscope, we investigate the atomic structure and decomposition pathway of CH3NH3PbI3 (MAPbI3) at the atomic scale. We successfully image the atomic structure of perovskite in real space under ultra-low electron dose condition, and observe a two-step decomposition process, i.e. initial loss of MA followed by the collapse of perovskite structure into 6H-PbI2 with their critical threshold dose also determined. Interestingly, an intermediate phase (MA0.5PbI3) with locally ordered vacancies can robustly exist before perovskite collapses, enlightening strategies for prevention and recovery of perovskite structure during degradation. Associated with structure evolution, the bandgap gradually increases from ~1.6 eV to ~2.1 eV, and it is found that both C-N and N-H bonds can be destroyed under irradiation, releasing NH3 and leaving hydrocarbons. These findings enhance our understanding of the photoelectric properties and failure mechanism of MAPbI3, providing potential strategy into material optimization.