Electronic band structure and carrier concentration of formamidinium–cesium mixed cation lead mixed halide hybrid perovskites

The electronic structure of hybrid perovskite compositions of FA0.83 Cs0.17 PbI3−xBrx (x = 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5) is determined using ultraviolet photoelectron spectroscopy (UPS) and UV–Vis–NIR absorption spectroscopy. With the help of UPS, ionization potential and Fermi energy are determined, and using absorption measurements, bandgap values are obtained. It is observed that for FA0.83 Cs0.17 PbI3−xBrx, as the Br content increases, the bandgap increases. The UPS measurements confirm the n-type nature of all compositions. Additionally, the Hall measurements were carried out for the selected compositions and the n-type carrier concentrations were determined.