Regulating the crystallization of mixed-halide perovskites by cation alloying for perovskite-organic tandem solar cells

Halide segregation and energy loss pose significant challenges for wide-bandgap perovskite solar cells, impairing their photovoltage and device stability. These issues are often exacerbated by inferior film quality and inhomogeneous halide distribution due to unbalanced crystallization processes. To address these challenges, we developed a novel strategy using a cation alloy that not only tailors the lattice properties and crystallization but also effectively passivates the defects. This approach enables homogeneous halide distribution and substantially reduced defect density. These improvements have led to a remarkable power conversion efficiency (PCE) of 19.50% with a record open-circuit voltage of 1.35 V for 1.79 eV perovskite solar cells, approaching similar to 90% of its S-Q limit. Furthermore, the champion device could maintain 93% of its initial efficiency after operating at its maximum power point for 500 hours. By integrating these perovskite devices into a monolithic perovskite-organic tandem solar cell (PO-TSC) as the wide-bandgap subcell, we demonstrated a high PCE of 25.54%. This efficiency is among the highest values reported for PO-TSCs, presenting a significant step forward in these promising tandem cells.