Hexagonal MASnI3 exhibiting strong absorption of ultraviolet photons

MASnI3, an organometallic halide, has great potential in the field of lead-free perovskite solar cells. Ultraviolet photons have been shown to generate deep trapping electronic defects in mesoporous TiO2-based perovskite, affecting its performance and stability. In this study, the structural, electronic, and optical properties of the cubic, tetragonal, and hexagonal phases of MASnI3 were studied using first-principles calculations. The results indicate that the hexagonal phase of MASnI3 possesses a larger indirect bandgap and a larger carrier effective mass along the c-axis compared to the cubic and tetragonal phases. These findings were attributed to enhanced electronic coupling and localization in the hexagonal phase. Moreover, the hexagonal phase exhibited high absorption of ultraviolet photons and high transmission of visible photons, particularly along the c-axis. These characteristics demonstrate the potential of hexagonal MASnI3 for application in multijunction perovskite tandem solar cells or as coatings in mesoporous TiO2-based perovskite solar cells to enhance ultraviolet stability and photon utilization.