Diammonium Cations in the FASnI₃ Perovskite Structure Lead to Lower Dark Currents and More Efficient Solar Cells

Hybrid halide perovskite solar cells with mixed cations demonstrate superior optical and electrical properties, especially for lead-based perovskite devices. Here, we report lead-free tin-based perovskite solar cells with diammonium cations, which can significantly improve the device performance. Formamidinium tin iodide (FASnI3) perovskite can incorporate propylenediammonium (PN) and trimethylenediammonium (TN) and retain its three-dimensional structure while at the same time providing better film morphology and optoelectronic properties. As a result, solar cell devices using FASnI3 absorbers mixed with 10% PN and 10% TN achieve higher power conversion efficiencies of 5.85% and 5.53%, respectively, compared to 2.53% of the pristine FASnI3 solar cell. This difference in device performance can be mainly attributed to the reduced leakage current, lower trap-state density, and reduced recombination, as evidenced by our dark current–voltage, space-charge-limited current, and impedance measurements. The results suggest that perovskite absorbers with mixed diammonium cations are beneficial in achieving high-performance perovskite solar cells.