Properties of FAPbI3-Based Alloy Perovskite Thin Films and Their Application in Solar Cells

Surface morphologies, light harvesting abilities, crystal structures, and excitonic properties of the formamiminium lead triiodide (FAPbI3) based alloy perovskite thin films were investigated by using the scanning electron microscopic images, absorbance spectra, X-ray diffraction patterns, photoluminescence (PL) spectra and time-resolved PL decaying curves. Our experimental results show that the fresh CsxFA1−xPbI3, RbxFA1−xPbI3, and FAPb(SCNxI1−x)3 alloy thin films are a pure α-phase perovskite crystal, a α-phase: δ-phase mixed perovskite crystal, and a PbI2 crystal/α-phase: δ-phase mixed perovskite crystal at room temperatures, respectively. Among the three FAPbI3 based alloy perovskite solar cells, the CsxFA1−xPbI3 solar cells have the better photovoltaic responses. It is noted that the high photocurrent density is mainly due to the formation of cube-like surface morphology and the long carrier lifetime of 368 ns when the CsxFA1−xPbI3 alloy perovskite thin film is used as the light-absorbing layer. Our findings provide the relation between the properties of the FAPbI3 based alloy perovskite thin films and the photovoltaic responses of the resultant solar cells.