Layer-by-Layer Degradation of Methylammonium Lead Tri-iodide Perovskite Microplates

Zheng Fan(1,2), Hai Xiao(3), Yiliu Wang(2), Zipeng Zhao(1), Zhaoyang Lin(2), Hung-Chieh Cheng(1), Sung-Joon Lee(1), Gongming Wang(2), Ziying Feng(2), William A. Goddard III(3), Yu Huang(1,4), Xiangfeng Duan(2,4), 2017

Image courtesy of Joule

Abstract

The methylammonium lead iodide (MAPbI3) perovskite has attracted considerable interest for its high-efficiency, low-cost solar cells, but is currently plagued by its poor environmental and thermal stability. To aid the development of robust devices, we investigate here the microscopic degradation pathways of MAPbI3 microplates. Using in situ transmission electron microscopy to follow the thermal degradation process, we find that under moderate heating at 85°C the crystalline structure shows a gradual evolution from tetragonal MAPbI3to trigonal lead iodide layered crystals with a fixed crystallographic direction. Our solid-state nudged elastic band calculations confirm that the surface-initiated layer-by-layer degradation path exhibits the lowest energy barrier for crystal transition. We further show experimentally and theoretically that encapsulation of the perovskites with boron nitride flakes suppresses the surface degradation, greatly improving its thermal stability. These studies provide mechanistic insight into the thermal stability of perovskites that suggests new designs for improved stability.

Impact Statement

The authors studied the degradation mechanism of perovskites exposed to higher temperatures in HiVac and dry air and find the degradation is a surface reaction layer-bylayer transition in the perovskite. Knowing this, the authors are able to sevelop a strategy to decrease this degradation usning encapsulatin. This has the potential to imporve the lifetime of perovskites.