Unveiling the origin of multiple peak emission in derivative perovskite single crystals, CH3NH3Pb(Br1-xClx)3 (x=0-1)

Despite the overwhelming success of organic-inorganic metal halide perovskites in the field of energy harvesting, many of the aspects of these materials are not well understood even now. Specifically, the origin of multiple peaks emergence in photoluminescence (PL) spectra is widely debated. In the present work, emission spectra of mix halide perovskites, MAPb(Br1-xClx)(3) (x = 0-1) on single crystal samples, have been investigated in detail. In addition to the band-to-band transition peak, two other peaks were observed. The amplitude of these two additional peaks appears to be strongly dependent on halide composition. Observed extra peaks in PL spectra were seen to be less pronounced in the pure end compositions (x = 0 and 1) and intense for intermediate compositions. It has been observed that multiple peaks seen in the bulk emission spectra are closely related to the coordination chemistry of a halide anion. X-ray absorption near edge spectroscopy indicated the existence of a different environment for the bromine anion, which might be responsible for the modification in the electronic structure with the change in halide composition. This modification in the electronic structure is suggested to be responsible for the appearance of debated multiple peak emissions in the PL spectra. These results are anticipated to pave the way for further research to enhance the understanding of the optoelectronic properties of mixed halide perovskites.