Study of photo-induced charge transfer properties in Cs₃Bi₂I₉/BiFeO₃/TiO₂ film

Inorganic lead-free perovskite Cs₃B_i2I₉ has attracted extensive attention due to its enhanced stability and environmental friendliness. However, the photon-to-current conversion of Cs₃B_i2I₉ perovskites is not efficient, partly due to inefficient electron-hole separation. In this manuscript, BiFeO₃ was deposited at the interface of Cs₃Bi₂I₉/TiO₂ as the interface modifier by sol–gel method, and the photocurrent and responsiveness of the Cs₃B_i2I₉/BiFeO₃/TiO₂ were significantly higher than those of the Cs₃B_i2I₉/TiO₂ based device. Kelvin probe force microscope, photoelectrochemical impedance spectroscopy and in-situ surface photovoltage spectra demonstrated that a self-polarized electric field of BiFeO₃ contributed to the separation of photogenerated charge carriers at the Cs₃B_i2I₉/TiO₂ interface. By analyzing the surface photovoltage phase spectra via a vector model method, complicated surface photovoltage processes were identified, and a detailed relationship between photocurrent generation and transfer characteristic of the photogenerated charge carriers have been discussed.