Impact of grain boundaries on efficiency and stability of organic-inorganic trihalide perovskites

Zhaodong Chu,Edward Seifert,Xiaoqin Li,Liuyang Sun,Keji Lai,Philip Schulz,Mengjin Yang,Kai Zhu,Di Wu,Xin Ma

doi:10.1038/s41467-017-02331-4

Abstract

Organic–inorganic perovskite solar cells have attracted tremendous attention because of their remarkably high power conversion efficiencies. To further improve device performance, it is imperative to obtain fundamental understandings on the photo-response and long-term stability down to the microscopic level. Here, we report the quantitative nanoscale photoconductivity imaging on two methylammonium lead triiodide thin films with different efficiencies by light-stimulated microwave impedance microscopy. The microwave signals are largely uniform across grains and grain boundaries, suggesting that microstructures do not lead to strong spatial variations of the intrinsic photo-response. In contrast, the measured photoconductivity and lifetime are strongly affected by bulk properties such as the sample crystallinity. As visualized by the spatial evolution of local photoconductivity, the degradation process begins with the disintegration of grains rather than nucleation and propagation from visible boundaries between grains. Our findings provide insights to improve the electro-optical properties of perovskite thin films towards large-scale commercialization.

Highlights

Organic–inorganic perovskite solar cells have attracted tremendous attention because of their remarkably high power conversion efficiencies
As material stability continues to be the key challenge faced by the perovskite solar cells (PSCs) community[8], an immediate question is whether the grain boundaries (GBs) and/or the surface of perovskite films are the weakest points where the degradation would start first
We report the first quantitative microwave impedance imaging with light stimulation on two MAPbI3 thin films with different power conversion efficiency (PCE) capped by a polymethyl methacrylate (PMMA) protection layer

Summary

Introduction

Organic–inorganic perovskite solar cells have attracted tremendous attention because of their remarkably high power conversion efficiencies. The worldwide surge of research interest in organic–inorganic trihalide perovskites, e.g., methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3), has led to a phenomenal increase of the power conversion efficiency (PCE) of perovskite solar cells (PSCs) from 3.8 to 22% in the past few years[1,2,3,4,5,6] These hybrid organic–inorganic thin films are polycrystalline in nature and compatible with low-cost solution or vapor-based processes[7,8,9]. Both the surface topography and local photoconductivity have been monitored over an extended period of time, which sheds new light on the intricate degradation process of the PSC devices

Methods

Results

Conclusion