Influence of light and humidity on the synthesis and characterization of perovskite FAPbI₃ thin films

Perovskite solar cells have gained more popularity in recent years because of their high efficiency and low cost. The most widely employed active layer in perovskite solar cells is FAPbI₃, which possesses higher stability, efficiency, and smaller bandgap value. However, its sensitivity to light and humidity makes it challenging to prepare under normal conditions in an economical manner. In this paper, we tried to control not only humidity during the annealing stage but also light intensity conditions of FAPbI₃ samples. Here, we synthesize samples in four different ways: (i) Without dark annealing; (ii) Vacuum-assisted without dark annealing; (iii) Dark annealing; and (iv) Vacuum-assisted dark annealing. Among these methods, Dark annealing and Vacuum-assisted dark annealing are two effective methods where we controlled light during the annealing stage. The morphological, structural, and optical characteristics of the samples were investigated. The FTIR data showed that the relative humidity of the sample is favourably reduced for the samples prepared using vacuum-assisted methods. X-ray analysis confirmed the α phase of FAPbI₃, which is a favourable phase for solar cell applications. The FESEM analysis confirmed the defect-free morphology of the prepared sample. The prepared α- FAPbI₃ accounts for a bandgap value of 1.51 eV, which is quite close to the ideal bandgap value. The α phase of FAPbI₃ is also conformed from TEM analysis. Thermal stability of sample was analysed by TGA/DTA and got a decomposition temperature of 442 °C.