Computational and experimental evaluation of bismuth modification in CsPbX3 (X = I− or Br−): Impact on structural and optical properties

In this work, the effects of partial substitution of Pb 2+ by Bi 3+ at the B-site of CsPbI 3 and CsPbBr 3 perovskites on their structural and optical properties were evaluated using an integrated approach combining Density Functional Theory (DFT) calculations and experimental results. DFT was employed as a reference for an ideally Bi-doped structure, enabling comparison with experimental bandgap values obtained by UV–Vis spectroscopy and diffuse reflectance, as well as structural phases determined by X-ray diffraction (XRD). Pure and modified perovskites were synthesized via a simple solvent engineering method under ambient and high-humidity conditions, without the use of a glovebox or controlled atmosphere. Structural, morphological, and optical characterizations were performed using XRD, SEM-EDS, UV–Vis, and DRS. The results indicate that bismuth affects the initial modulation of the crystal structure, influencing optical properties and inducing bandgap variations. Moreover, the system evolves towards a phase-segregated state over time, associated with the lower thermodynamic stability of trivalent cation incorporation into the perovskite lattice. The modified samples exhibit an enhanced optical response, suggesting the potential of Bi doping for tuning properties relevant to photovoltaic applications.