Europium redox doping to suppress Sn-I defect pairs in Sn perovskite photovoltaics

Preventing the formation of Sn-I defect pairs is of vital importance for the fabrication of stable and efficient Sn perovskite solar cells (PSCs). This has spurred intensive efforts, which leave a formidable challenge of simultaneously addressing the unfavored chemical activities of Sn2+ and I− in Sn perovskites. Herein, we report a europium (Eu) redox-doping method that leverages the facile reactions between Eu2+, Sn4+, and I0 in the acidic environment of perovskite solution and thus alleviates the Sn-I defect pair issue. Experimental and theoretical investigations suggest that Eu2+ could enter Sn perovskite lattice, altering the geometric and electronic structures of [SnI6]4− octahedra. This could reduce the energy barrier for charge transfer along the inorganic framework. Sn-PSCs with Eu redox doping deliver power conversion efficiencies up to 13.66% and improved stabilities.