Operationally Stable Perovskite/Silicon Tandem Solar Cells via Suppression of Lead Iodide‐Mediated Phase Segregation in Wide‐Bandgap Perovskites

Abstract Phase segregation in wide‐bandgap mixed‐halide perovskites remains a critical bottleneck for the operational stability of solar cells, including tandem architectures. While lead iodide (PbI 2 ) segregation at grain boundaries during crystallization is now recognized as a key driver of this degradation, strategies to suppress its formation at the source remain underexplored. Here, this challenge is addressed by modulating perovskite crystallization through in situ crosslinking additive engineering. The formation of crosslinked polymer networks immobilized Pb‐related frameworks to promote a more complete perovskite phase transformation with PbI 2 suppression. These networks are uniformly distributed throughout the perovskite grain boundaries, concurrently passivate defects and inhibit ion migration, thereby phase segregation in perovskites. This approach enables 1.68‐eV perovskite solar cells to achieve a power conversion efficiency of 23.03% with enhanced operational stability, retaining more than 90% of initial performance after 1100 h under maximum power point tracking. Integrated perovskite/silicon tandem cells deliver a certified efficiency of 32.57% (certified 32.41%) in 1‐cm 2 area with 90% retention after 1400 h of illumination testing at an elevated temperature of 45 °C.