The State Key Lab of
High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences
中 国 科 学 院 上 海 硅 酸 盐 研 究 所 高 性 能 陶 瓷 和 超 微 结 构 国 家 重 点 实 验 室
Photo-induced Ferroelectric Switching in Perovskite CH3NH3PbI3 Films
The photovoltaic conversion efficiency of perovskite solar cells based on organic-inorganic CH3NH3PbI3 has risen spectacularly from 3.8% to over 22% in just seven years, yet quite a few important fundamental issues have not been settled, and the role of spontaneous polarization remains poorly understood. While piezoresponse force microscopy (PFM) has been adopted to probe possible ferroelectricity in CH3NH3PbI3, the reported data are often conflicting and inconclusive, due to complexity in apparent piezoresponse and its switching that may arise from ionic motions, electrostatic interactions, and other electromechanical mechanisms. Herein, using a combination of microscopic and macroscopic measurements, we unambiguously establish the linear piezoelectricity of CH3NH3PbI3 arising from its spontaneous polarization, which can be switched by an electric field, though other electromechanical contributions, such as ionic motions are also shown to exist. More importantly, we demonstrate strong interactions between polarization and light in technologically relevant CH3NH3PbI3 films with good conversion efficiencies, observing that the spontaneous polarization can also be switched by light illumination in the absence of electric field, and the photo-induced surface charges and potentials are shifted by the spontaneous polarization. This set of studies offer strong evidence on the interactions among photo-induced charges, polarization, and possibly ions in perovskite CH3NH3PbI3, and these fundamental observations lay the ground for answering the technologically important question regarding the effects of ferroelectricity on its photovoltaic conversion.