Photo-induced ferroelectric switching in perovskite CH3NH3PbI3films.
The photovoltaic conversion efficiency of perovskite solar cells based on organic-inorganic CH3NH3PbI3has risen spectacularly from 3.8% to over 20% 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 the complexity in the apparent piezoresponse and its switching that may arise from ionic motions, electrostatic interactions, and other electromechanical mechanisms. Here, using a combination of microscopic and macroscopic measurements, we unambiguously establish the linear piezoelectricity of CH3NH3PbI3arising 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 CH3NH3PbI3films with good conversion efficiencies, observing that the spontaneous polarization can also be switched by light illumination in the absence of an electric field. The light is shown to reduce the coercive voltage of CH3NH3PbI3and shifts its nucleation bias, suggesting that the photo-induced switching is caused by ionic motions in combination with a photovoltaic field. This set of studies offer strong evidence on the interactions among photo-induced charges, polarization, and 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.
Department of Mechanical Engineering, University of Washington, Seattle, WA 98195-2600, USA.
Peiqi
P
Wang
Department of Mechanical Engineering, University of Washington, Seattle, WA 98195-2600, USA and School of Materials Science and Engineering, and Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China. jinjinzhao2012@163.com and Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, Guangdong, China. jjli@uw.edu.
Jinjin
J
Zhao
School of Materials Science and Engineering, and Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China. jinjinzhao2012@163.com.
Liyu
L
Wei
Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education, School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, Hunan, China.
Qingfeng
Q
Zhu
Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, Guangdong, China. jjli@uw.edu and Key Laboratory of Low Dimensional Materials and Application Technology of Ministry of Education, School of Materials Science and Engineering, Xiangtan University, Xiangtan 411105, Hunan, China.
Shuhong
S
Xie
School of Materials Science and Engineering, and Department of Engineering Mechanics, Shijiazhuang Tiedao University, Shijiazhuang, 050043, China. jinjinzhao2012@163.com.
Jinxi
J
Liu
National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China.
Xiangjian
X
Meng
Department of Mechanical Engineering, University of Washington, Seattle, WA 98195-2600, USA and Shenzhen Key Laboratory of Nanobiomechanics, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, Guangdong, China. jjli@uw.edu.
Jiangyu
http://orcid.org/0000-0003-0533-1397
J
Li