Surface field effect probed by THz emission in lead-free perovskite CsSnBr3 films and CsSnBr3/SiO2/Si heterojunction

Abstract

The surface field effect plays a crucial role in determining the performance of perovskite-based devices, which have attracted considerable interest in the field of photoelectric and photovoltaic applications. Nevertheless, conventional measurement techniques provide restricted understanding regarding surface properties. Herein, terahertz (THz) emission spectroscopy is employed to investigate the surface effects of lead-free CsSnBr₃ perovskite films and the CsSnBr₃/SiO₂/Si heterojunction. Our findings validate the significant role played by surface effects in the underlying mechanisms of THz wave generation. Specifically, under femtosecond laser excitation with photon energy above the bandgap, THz waves are emitted due to transient photocurrents induced by the surface depletion electric field and resonant optical rectification in the surface region. Under below-bandgap excitation, the mechanism of THz emission is primarily attributed to the nonlinear polarization effect. Moreover, by utilizing THz emission as a probe, we investigate the photocarrier transport behavior and surface potential variation at interfaces adjacent to the CsSnBr₃/SiO₂/Si heterojunction, providing valuable insights into the presence of depletion and inversion states in the surface layer. This work underscores the significance of surface effects and THz emission in perovskite research, while also paving the way for developing tunable optoelectronic applications based on perovskites.