Investigation of the optoelectronic and structural properties of FA(1−x)BixPbBr6I3 of perovskite mixed halide films

Abstract

In this study, we analyzed the structural and optical characteristics of pure FAPbBr2I mixed halide perovskites and doped with a large proportion of bismuth. Previous work has demonstrated that the replacement of 2/3 of the iodine by bromine in the perovskite FAPbI3 limits its phase transition and thus increases its stability. However, this improvement in stability is accompanied by an increase in the band gap, from 1.45 to about 2 eV. It has been found that bismuth doping of certain perovskite materials makes it possible, in addition to increasing their stability, to significantly reduce their band gap, although certain authors still contest this phenomenon. Thus, we synthesized thin layers of perovskite FAPbBr2I doped with bismuth and studied the effect of this doping on the crystalline structure and the layers' optical characteristics thanks to analyses by X-ray diffraction, scanning electron microscopy and measurements of absorption and photoluminescence. The structural analysis results showed that bismuth diffuses very slowly into the crystal, resulting in a reduction in crystal size and a smoother surface. Moreover, measurements of the absorption coefficient revealed a significant reduction in the band gap, going from 2.08 eV with 0% bismuth to 1.45 eV with 20% bismuth. However, photoluminescence measurements gave much higher bandgap values. We believe that a phenomenon related to the addition of bismuth is responsible for this discrepancy.