Heterogeneous FASnI3 Absorber with Enhanced Electric Field for High-Performance Lead-Free Perovskite Solar Cells

Lead-free tin perovskite solar cells (PSCs) have undergone rapid development in recent years and are regarded as a promising ecofriendly photovoltaic technology. However, a strategy to suppress charge recombination via a built-in electric field inside a tin perovskite crystal is still lacking. In the present study, a formamidinium tin iodide (FASnI(3)) perovskite absorber with a vertical Sn2+ gradient was fabricated using a Lewis base-assisted recrystallization method to enhance the built-in electric field and minimize the bulk recombination loss inside the tin perovskites. Depth-dependent X-ray photoelectron spectroscopy revealed that the Fermi level upshifts with an increase in Sn2+ content from the bottom to the top in this heterogeneous FASnI(3) film, which generates an additional electric field to prevent the trapping of photo-induced electrons and holes. Consequently, the Sn2+-gradient FASnI(3) absorber exhibits a promising efficiency of 13.82% for inverted tin PSCs with an open-circuit voltage increase of 130 mV, and the optimized cell maintains over 13% efficiency after continuous operation under 1-sun illumination for 1,000 h.

Automated summary

Lead-free tin perovskite solar cells have shown rapid development and promising efficiency, with the fabrication of a formamidinium tin iodide perovskite absorber with a vertical Sn2+ gradient to enhance the built-in electric field. The depth-dependent X-ray photoelectron spectroscopy revealed an increase in efficiency and open-circuit voltage for the tin PSCs, even after continuous operation under 1-sun illumination for 1,000 hours.