Decoupling engineering of formamidinium-cesium perovskites for efficient photovoltaics

Haoran Chen; Yong Wang; Yingping Fan; Yuetian Chen; Yanfeng Miao; Zhixiao Qin; Xingtao Wang; Xiaomin Liu; Kaicheng Zhu; Feng Gao; Yixin Zhao

doi:10.1093/nsr/nwac127

Decoupling engineering of formamidinium-cesium perovskites for efficient photovoltaics

Natl Sci Rev. 2022 Jul 5;9(10):nwac127. doi: 10.1093/nsr/nwac127. eCollection 2022 Oct.

Authors

Haoran Chen¹, Yong Wang², Yingping Fan¹, Yuetian Chen¹, Yanfeng Miao¹, Zhixiao Qin¹, Xingtao Wang¹, Xiaomin Liu¹, Kaicheng Zhu¹, Feng Gao², Yixin Zhao^{1

3}

Affiliations

¹ School of Environmental Science and Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai 200240, China.
² Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping 58183, Sweden.
³ Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200240, China.

Abstract

Although pure formamidinium iodide perovskite (FAPbI₃) possesses an optimal gap for photovoltaics, their poor phase stability limits the long-term operational stability of the devices. A promising approach to enhance their phase stability is to incorporate cesium into FAPbI₃. However, state-of-the-art formamidinium-cesium (FA-Cs) iodide perovskites demonstrate much worse efficiency compared with FAPbI₃, limited by the different crystallization dynamics of formamidinium and cesium, which result in poor composition homogeneity and high trap densities. We develop a novel strategy of crystallization decoupling processes of formamidinium and cesium via a sequential cesium incorporation approach. As such, we obtain highly reproducible, highly efficient and stable solar cells based on FA₁ _- _x Cs _x PbI₃ (x = 0.05-0.16) films with uniform composition distribution in the nanoscale and low defect densities. We also revealed a new stabilization mechanism for Cs doping to stabilize FAPbI₃, i.e. the incorporation of Cs into FAPbI₃ significantly reduces the electron-phonon coupling strength to suppress ionic migration, thereby improving the stability of FA-Cs-based devices.

Keywords: decoupling engineering; formamidinium–cesium; perovskite solar cell; sequential cesium incorporation; uniform composition distribution.