Effect of Halogen-Doping on Properties of Bismuth Iodide (BiI3) Optical Absorption Layer

Bismuth tri-iodide (BiI 3 ), a promising lead-free photoelectric semiconductor material, is suitable for photovoltaic applications. Herein, the effect of halogen doping with bromine (Br) and chlorine (Cl) compounds on the morphology and photovoltaic performances of BiI 3 thin films is investigated. BiI 3− x X x films doped with halogens are prepared by vacuum thermal evaporation. Scanning electron microscope (SEM) shows that with the increase in doping ratio, the morphology of the thin film changes significantly, which is conducive to the contact with the cavity conduction layer. The bandgap increases from ≈1.75 to 1.78 eV (BiI 2.91 Cl 0.09 ) and 2.06 eV (BiI 2.91 Br 0.09 ) after doping. X-ray photoelectron spectroscopy (XPS) shows that the band position of the two doped films increases, which is more conducive to the realization of band matching. The films with higher properties are obtained by doping halogens, and the maximum (BiI 2.91 X 0.09 ) photocurrent is twice of the minimum (BiI 2.97 X 0.03 ). The maximum photocurrent obtained by photocurrent I – T test is 0.043 Ma cm −2 (BiI 2.91 Cl 0.09 ) and 0.047 mA cm −2 (BiI 2.91 Br 0.09 ).