Oriented Perovskite Crystal towards Efficient Charge Transport in FASnI₃ Perovskite Solar Cells

Despite a higher power conversion efficiency (PCE) than other lead-free perovskite solar cells (PSCs) due to intrinsically excellent optoelectronic properties and suitable bandgaps of tin (Sn) perovskites, Sn-based PSCs still suffer from issues of stability and efficiency for practical applications. Herein, a novel strategy of tuning perovskite crystal orientation toward ≈45° with respect to the substrate by doping 2,3-diaminopropionic acid monohydrochloride (2,3-DAPAC) into formamidinium tin iodide (FASnI₃) is proposed, which facilitates charge transport in the perovskite film and consequent device performances. In addition, the incorporation of 2,3-DAPAC into FASnI₃ enables dense and smooth high-quality perovskite films with less Sn vacancies. Applications of the 2,3-DAPAC-treated FASnI₃ films into PSCs acquire a champion PCE of 7.23%, showing 37.2% enhancement compared with 5.27% of the control device. Moreover, the storage stabilities of both perovskite films and PSCs are significantly prolonged with improved film quality.