A Universal Strategy to Stabilize Crystal Lattice and Composition of Wide‐Bandgap Perovskites for Efficient Tandem Solar Cells

The film quality of wide-bandgap (WBG) perovskites is critical for achieving high-efficiency perovskite/organic tandem solar cells (POTSCs). However, the Br-rich WBG perovskites often suffer from inhomogeneous crystallization, leading to severe phase-segregation and substantial non-radiative energy losses. Here, cyanates are rationally designed to modulate the crystallization of WBG perovskites. RbOCN is successfully incorporated into the perovskite crystal lattice, optimizing the cation-anion composition distribution, reducing the lattice constant, and inducing a blue-shift in the band edge. These synergistic effects produce highly crystalline, phase-stable WBG perovskites, yielding an impressive efficiency of 22.45% for a 1.73 eV perovskite device (0.09 cm²). Moreover, RbOCN exhibits broad applicability across WBG perovskites with varying band gaps (1.79 eV, 1.85 eV, and 1.92 eV). These optimized sub-cells are subsequently integrated with organic sub-cells to fabricate POTSCs. Benefiting from well-aligned spectral responses, an exceptional efficiency of 26.75% is achieved for POTSCs (0.09 cm²) based on 1.85 eV perovskite sub-cells. Notably, the strategy demonstrates excellent scalability, delivering an impressive efficiency of 25.37% and a record open-circuit voltage of 2.22 V for 1 cm² POTSCs. This study establishes a robust approach for mitigating inhomogeneous crystallization and stabilizing the crystal lattice in WBG perovskites, thereby advancing the development of high-performance TSCs.