Suppression of Defect and Trap Density through Dimethylammonium-Substituted Tin Perovskite Solar Cells

Lead-free perovskite solar cells have attracted attention to many in the field of perovskite research due to environmental concern over toxic materials and standards compliance. Tin-based perovskite materials have been selected as the ideal alternative to lead-based perovskite due to their similar optoelectronic properties. However, the performance of tin perovskite solar cells is still much lower than their lead perovskite counterparts. Various strategies have been introduced in order to enhance the efficiency of tin perovskite solar cells. In this research, A-site cation substitution has been performed using dimethylammonium cation (DMA+) in the form of dimethylammonium iodide (DMAI) salt. An optimized concentration of DMAI enhanced the performance of tin perovskite solar cells to a more than 10% boosted higher open-circuit voltage (VOC). A better surface morphology was obtained with DMA+ substitution. From Mott–Schottky measurements, a higher built-in potential has been obtained, which helped with charge carrier extraction. Furthermore, from X-ray photoelectron spectroscopy measurements, tin oxidation has been suppressed, leading to low hole carrier density. This work provides evidence that controlling the charge carrier density in tin-based perovskite solar cells is important to fabricating high performance devices.