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 (FASnI 3 ) 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 FASnI 3 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 FASnI 3 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.