Fabrication and characterization of lead-free Cs₂SnI₆ perovskite films for photovoltaic applications

Cs₂SnI₆ has recently been reported as a promising material to replace Pb-based perovskite materials due to its appropriate optical and electrical properties as well as high stability in the ambient environment. Here, the study focuses on introducing different types of reactants to form highly stable Cs₂SnI₆ films via a modified two-step process. The structural analysis was examined using the X-ray diffraction measurements and lattice strain and average crystallite size were calculated by the Williamson hall method. All the prepared films showed excellent phase stability at 210°C with no major CsI impurity peak. Adding excess I₂ with SnI₄ at 225°C resulted in inhibiting the decomposition of the film. Raman measurements revealed the presence of three first-order modes at 78, 92, 126 cm⁻¹, and a higher mode at 248 cm⁻¹, respectively. The UV-vis results confirm the direct semiconductor nature of Cs₂SnI₆ with bandgap ranging from 1.31-1.37 eV. The iodine-rich preparation of the films resulted in improved photoluminescence and high hole mobility of 329 (cm²V⁻¹ s⁻¹). The present work will provide useful guidance in the preparation protocol of Cs₂SnI₆ perovskite solar cells.