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Lead iodide (PbI 2 )-rich methylammonium lead bromide-iodide (MAPb(I 1– x  Br  x  ) 3 ) thin-films were prepared by sequential physical vapor deposition of methylammonium lead tri-bromide (MAPbBr 3 ) on methylammonium lead tri-iodide (MAPbI 3 ) bottom layer. The structural, optical, morphological, and electrical properties of the thin-films were studied as the thickness of methylammonium bromide (MABr) was increased from 300 to 500 nm. X-ray diffractograms confirmed transformation of tetragonal MAPbI 3 ( x  is 0.0) to the cubic-like structure of MAPbBr 3  ( x  is 1.0) as MAPb(I 1– x  Br  x  ) 3  ( x  = 0.89–0.95) and PbI 2  were formed. The bromine mole ratio  x  decreased as MABr thickness increased. UV-Vis absorption spectra showed that the bandgap of the thin alloy film decreased from 2.21 to 2.14 eV as  x  decreased. Scanning electron micrographs depicted densely packed grains that entirely covered the substrate and contained very few pinholes. The average grain size increased from 150 to 320 nm as  x  decreased. Electrical properties showed high charge carrier mobility that increased linearly with MABr thickness. FTO/MAPb(I 1– x  Br  x  ) 3 /Au devices using fluorine-doped tin oxide (FTO) as substrate and gold (Au) as contacts were fabricated and current-voltage characteristics were determined. Space-charge-limited current theory was applied to charge carrier mobility and trap density of MAPb(I 1– x  Br  x  ) 3  thin-films. The charge carrier mobility increased as  x  decreased. The power conversion efficiency (PCE) of FTO/MAPbBr 3 /Au, FTO/MAPb(I 0.11 Br 0.89 ) 3 /Au and FTO/MAPbI 3 /Au solar cells were 0.56, 0.62, and 1.15%. Devices including titanium dioxide compact layer (c-TiO2) and titanium dioxide mesoporous (m-TiO 2 ) layer as electron transport layers were also fabricated for the application of Mott-Shottky (M-S) theory. Analyses of dark current-voltage and capacitance-voltage curves of FTO/c-TiO 2 /m-TiO 2 /MAPb(I 0.11 Br 0.89 ) 3  solar cells revealed a sizeable built-in voltage ( V   bi  ) of 1.6 V and an accumulation of charge at interfaces for voltages greater than 0.2 V, respectively. Similar analyses for FTO/TiO 2 /MAPbI 3 /Au showed a small  V   bi   of 0.7 V and no charge carrier at interfaces. The work paves a way for reproducible growth of MAPb(I 1– x  Br  x  ) 3  for solar cells and sheds more light on the degree of ion migration in mixed halide and pure halide perovskites.

Characterization of Thin MAPb(I1–xBrx)3 Alloy Halide Perovskite Films Prepared by Sequential Physical Vapor Deposition