The Fabrication of Lead-Free Cs₂SnI₆ Perovskite Films Using Iodine-Rich Strategy for Optoelectronic Applications

Parallel to the booming of all-inorganic CsPbX₃ halide perovskites, the growth of lead-free perovskites is accelerating, with the efficiency values of over 10% being realized. Eco-friendly and stable halide double perovskites with superior stability are considered as an encouraging alternative to address the stability concerns related to the lead halide perovskites. Recently, Cs₂SnI₆ with defect perovskite structure has appeared as a “superstar” material owing to its environmental friendliness and exceptional stability. Herein, an iodine-rich strategy (IRS) is developed based on the modified two-step method for the fabrication of lead-free Cs₂SnI₆ films. In addition, the impact of the reaction temperature on the properties of the resultant films is systematically investigated. The results reveal the improvement in the crystallinity and phase stability of the films, suggesting that the proposed IRS successfully inhibits the decomposition of Cs₂SnI₆ films. The optical measurements confirm the n-type nature of Cs₂SnI₆ with bandgap varying from 1.23 to 1.38 eV. The photoluminescence of the films increases gradually with the addition of I₂, presumably owing to the reduction of nonrecombination sites. The current work provides valuable direction for the fabrication of Cs₂SnI₆ devices for green energy applications.