Investigation of the stoichiometric deviation between the mixed cation, mixed halide lead perovskite thin film and its precursor solution

The compositional engineering of an organo-lead halide perovskite plays a crucial role in determining the versatility and stability of photovoltaic device performance, which is vital for its commercialization. Manipulating the ion composition of the perovskite ABX₃ crystal structure within a reasonable tolerance factor range allows for achieving tunable bandgaps and material stability. While perovskite solar cells have shown comparable performance to silicon crystalline solar cells, research groups pay little attention to the stoichiometry of the final perovskite film. The precise manipulation of perovskite's chemical composition is critical in determining its cell reproducibility. The UV-Vis spectrophotometer is a potent and widely used instrument for distinguishing precursors in solutions in various fields. Herein, we report for the first time that UV-Vis spectra are an applicable tool in determining the formulation of perovskite films. We demonstrate a successful method for separating the organic and inorganic components of the perovskite film, establishing calibration curves, and performing detailed calculations. Our findings reveal that the chemical composition of perovskite films does not match the proportion of the precursor solutions. This study could lay the groundwork for future research on quantifying perovskite films and explaining the high reproducibility trends observed in perovskite solar cells.