Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells using In-situ Synchrotron Radiation Analysis

Nam-Koo Kim,Gitaeg Jeong,Seh-Won Ahn,Seokhwan Noh,Kyuwook Ihm,Donghwan Kim,Minho Joo,Young Hwan Min,Jeong Soo Lee,Hyungju Ahn,Yoonmook Kang,Hae-Seok Lee,Seongtak Kim,Eunkyung Cho

doi:10.1038/s41598-017-04690-w

Abstract

In this study, we employ a combination of various in-situ surface analysis techniques to investigate the thermally induced degradation processes in MAPbI3 perovskite solar cells (PeSCs) as a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI3 perovskite film changes to an intermediate phase and decomposes to CH3I, NH3, and PbI2 after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH3NH3+ organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI3 perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.

Highlights

Solar cells have received a significant amount of attention as an environmentally friendly and safe next-generation energy source, and, to date, solar cell active layers have been fabricated, studied, and commercialised successfully using a variety of materials and architectures
In order to establish the cause of the decline in efficiency, we employed a combination of in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD), high-resolution X-ray photoelectron spectroscopy (HR-XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements to obtain information about the thermal degradation processes in the MAPbI3 perovskite
Single layer MAPbI3 perovskite films were sealed using the same procedure as shown in Fig. 1a, and the long-term stability of encapsulated MAPbI3 films was tested at 85 °C and 85% relative humidity (RH)

Summary

Introduction

Solar cells have received a significant amount of attention as an environmentally friendly and safe next-generation energy source, and, to date, solar cell active layers have been fabricated, studied, and commercialised successfully using a variety of materials and architectures. The modification of the perovskite structure from three-dimensional perovskite films to layered two-dimensional perovskite films using containing spacing layers has exhibited promising increase in stability to light soaking and humidity[20, 21] In addition to these concerted efforts in studying air-stability enhancement techniques, the degradation mechanisms of MA-based perovskites mediated by the presence of oxygen, moisture, and UV have been researched, suggesting a route towards perovskite solar cells with long device lifetime and resistance to ambient, atmospheric, and UV light[22,23,24,25,26,27]. In addition to the stability to air and light, thermal stability represents another key factor in the fabrication of solar cells and, currently, further improvements in thermal stability and investigations into the progress and mechanism of thermal degradation are required. The comprehensive results of our in-situ surface analysis provided a better understanding of the important factors that need to be taken into consideration in commercial applications and the parameters affecting the thermal stability of PeSCs under different environmental conditions

Methods

Results

Conclusion