Effect of Br-doping and choice of precursor solvent on morphology of lead free (CH3NH3)3Bi2I9 perovskites

Thin films of methyl ammonium iodobismuthate (MA(3)Bi(2)I(9), MBI) doped on the anion site with bromine (MA(3)Bi(2)I(9-x)Br(x)), with x in the range of 0.46-0.51, have been fabricated using a two-step solution processing method. The use of dimethyl sulfoxide (DMSO) leads to high coverage films in comparison to the films fabricated using N, N-dimethylformamide (DMF). Films fabricated with dimethyl sulfoxide (DMSO) as the precursor solvent have a similar microstructure, irrespective of Br doping. In addition, the Br doping of the phase pure MBI leads to a decrease in the lattice parameter, probably due to the smaller bromide ion. The power conversion efficiency increases using Br-doped films as an absorber layer as compared to pristine MBI films. The band alignment of the Br-doped film has been calculated by ultraviolet photoelectron spectroscopy. X-ray photoelectron spectroscopy results indicate that Br-doping could prove beneficial against surface reactions in a humid environment. Published by AIP Publishing.