Operando Spectroscopy Revealed the Formation Mechanism and Chemical Reaction of Lead Halide Perovskite Solar Cell Materials
Sun-Tang Chang1*, Yen-Chun Lai1,2, Chin-Yu Hsieh3, Cheng-Min Tsai4, Chia-Hsin Wang1, Eric Wei-Guang Diau4, Yaw-Wen Yang1,3
1National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Program of Science and Technology of Synchrotron Light Source, National Tsing Hua University, Hsinchu, Taiwan
3Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan
4Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:Sun-Tang Chang, email:suntang925@gmail.com
In this study, the in-situ X-ray photoelectron spectroscopy (XPS) coupled with mass spectrometry is utilized to elucidate the chemical reaction leading to perovskite during annealing processing. The XPS data indicate that the perovskite film is formed at temperature close to 80~100 oC in PbBr2-based and PbCl2-based system while it occurs at room temperature for PbI2-based system, evidenced by the “correct” binding energy values of Pb 4f7/2, Br 3d5/2 Cl 2p and I 4d5/2 core levels. When the annealing temperature goes over 120~160 oC, the perovskite decomposes into PbX2 (where X=I, Cl and Br) and Pb. Operando mass spectrometry study of evolved gaseous species shows that at high annealing temperature generation of HX (X=I, Cl and Br) and CH3NH2 molecules were observed. The present study offers a revealing insight into the formation of lead-based perovskite (PbI2, PbCl2 and PbBr2) and explains why higher annealing temperature is often needed for chloride- and bromide-based perovskites compared to its iodide counterpart. The study can be good a reference to improve the perovskite solar cell efficiency through optimization of annealing temperature.

Keywords: Perovskite solar cell, in-situ XPS, operando mass spectroscopy