What Limits the Performance of Tin Perovskite Solar Cells? A Perspective from Energy Levels and Interfacial Alignment

As the most promising alternative material to lead perovskites, tin perovskites have not completely realized their potential in solar cells. We analyze the origin of band edges in tin perovskites and reveal a general trend that the conduction band minimum (CBM) is primarily attributed to the Sn 5 p orbital energy and offset by the surrounding halide ions through Coulombic repulsion. Both conduction and valence band edges of tin perovskites are found to be higher positioned than their lead counterparts. To meet the new requirements for energy level alignment, transport materials commonly used with tin perovskites rely on special functional groups such as fullerene and poly(ethylenedioxythiophene) (PEDOT), but still with limitations. Development of transport materials with proper energy levels and carrier mobilities is expected to achieve further performance enhancement, and enable the n–i–p device structure for tin perovskite solar cells.