Thermal Stability of BiI3 Thin Films

Bismuth triiodide (BiI3) is a possible candidate to replace lead in perovskite-like materials for photovoltaic applications. Besides this applicability as an active layer in solar cells, BiI3 can also be converted, using methylammonium iodide, to the perovskite-like material MA3Bi2I9, that is also suitable for photovoltaic applications. Here we investigate the thermal stability of thermally evaporated BiI3 thin films annealead up to 150 °C in ambient atmosphere (in a closed oven in the absence of illumination). BiI3 films show similar X-ray diffratrograms with indexed peaks related to an R-3 rhombohedral crystal structure. The bandgaps of BiI3 thin films were determined by Tauc plots of transmittance data in UV-vis range and indicate a bandgap of 1.72 eV regardless of annealing temperature and suitable for photovoltaic applications. We verified that its morphological properties, observed through SEM images, are also not changed with respect to its annealing at temperatures up to 150 °C. Thereby, the structural, morphological and optical properties of annealing on thermally evaporated BiI3 are not considerably altered, the films retaining their properties when heated up to 150 °C, temperature higher than the operation temperature of solar cells and below the melting point of BiI3.