Bandgap tuning in lead halide perovskite thin films prepared under an air ambience

Generally, the inorganic lead halide perovskite (LHP) cubic CsPbI 3 is synthesized under inert atmosphere at about 320 °C, but it rapidly degrades to its undesired phases by lowering the temperatures. This study presents the successful preparation of CsPbI 3-x Br x (x = 0, 0.5, 1, 1.5, 2, 2.5, and 3) thin films through additive engineering with polyvinylpyrrolidone (PVP) using spin coating method under an ambient air atmosphere at a low annealing temperature of about 120 °C. Preliminary X-ray diffraction (XRD) pattern study provides the information on successful formation of cubic phase of the perovskites. The room temperature Raman spectra confirm that there is no appearance of vibrational modes as a signature for cubic phase of the synthesized inorganic LHPs. The energy bandgap using UV-Vis spectroscopy through Tauc plot is tuned in between 1.76 eV (x = 0) to 2.35 eV (x = 3) which is also confirmed by steady-state photoluminescence emission spectra study. Furthermore, charge carrier lifetime of the typical CsPbBr 3 perovskite thin film (10.63 ns ) obtained by time-resolved PL spectroscopy is higher than the reported ones, indicating the reduction of non-radiative charge carrier recombination. Therefore, the prepared cubic phase of CsPbI 3-x Br x LHP thin films stable more than 200 h at ambient-air under dark conditions may be applicable to develop inorganic perovskite-based photovoltaics.