Bandgap tuning of MAPbI3−XBrx thin film perovskites for photovoltaic applications

Mixed bromide-iodide methylammonium lead-halide perovskites have been synthetized from methylamine, lead nitrate and the corresponding hydroX acid (X= I, Br) precursors and thereafter deposited as thin films onto FTO substrates by spin coating or dipping. Thin film perovskites were then characterized by X-Ray Diffraction, optical spectrometry and photoluminescence. All synthetized MAPbI3, MAPbBr3 and mixed MAPbI3-iBri perovskites crystallized in the same cubic phase irrespective of the halide component and a unique phase is observed. From transmittance and reflectance spectral measurements we have inferred the bandgap of thin film perovskites, obtaining a bandgap of about 1.58 and 2.35 eV for I and Br, respectively. The optical bandgap of mixed thin film perovskites was tuned by changing the halide composition of the perovskite precursor solution in the desired proportions. Afterwards bandgap values were confirmed by photoluminescence emission. Results of preliminary photovoltaic devices will be presented.