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

Inorganic lead-free perovskite Cs3Bi2I9 has attracted extensive attention due to its enhanced stability and environmental friendliness. However, the photon-to-current conversion of Cs3Bi2I9 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 Cs3Bi2I9/BiFeO3/TiO2 were significantly higher than those of the Cs3Bi2I9/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 Cs3Bi2I9/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.