Photoinduced Ultrafast Electron Transfer and Charge Transport in a PbI2/C60 Heterojunction

Abstract

Charge transport and electron transfer in a PbI2/C60 heterojunction were investigated. The charge carrier mobilities and trap densities of PbI2 were extracted from current–voltage characteristics of hole- and electron-only devices. Femtosecond transient absorption spectroscopy was used to elucidate the photophysical processes occurring in the heterojunction. For a pristine PbI2 film, trap-limited bimolecular recombination was the dominant mechanism in the case of low pump fluence. We observed photoinduced ultrafast electron transfer from PbI2 to C60 with a rate constant of 0.45 ps–1. Semiclassical Marcus electron transfer theory was used to estimate the electronic coupling between the conduction band edge of PbI2 and the lowest unoccupied molecular orbital of C60. We also fabricated a solar cell using the PbI2/C60 heterojunction. Electron transfer and charge extract efficiencies in our cell were also deduced. The performance-limiting factors for solar cells based on PbI2 were discussed and a strategy to improve the device performance was developed. Our work is useful for ultraviolet-harvesting transparent solar cells and other photophysical and photochemical applications.