Targeted Enhancement of Passivator Coordination Activity Enables 2.00 V V oc in Efficient Perovskite/Silicon Tandem Solar Cells

ABSTRACT Perovskite/silicon tandem solar cells are the leading next‐generation photovoltaic technology. Wide‐bandgap perovskite top cells are crucial for high‐performance tandem cells, yet significant open‐circuit voltage loss due to high defect density and insufficient crystallinity remains a critical bottleneck. While phosphine oxide (P═O) moieties serve as effective defect passivators, conventional single P═O species lack sufficient reactivity to achieve efficient defect passivation and crystallization regulation. Herein, we propose a universal molecular design strategy based on phosphorus‐oxygen bonds. Incorporation of electron‐donating alkyl substituents into the molecular backbone of the additive enhances the electron density of the P═O bond, thereby strengthening its coordination and passivation capabilities. This targeted electron modulation strengthens phosphorus oxide–perovskite interactions, suppressing non‐radiative recombination. Additionally, the electron‐optimized structure enhances intermolecular interactions with perovskite precursors, favoring regulated crystallization. Consequently, the V oc of the perovskite/silicon tandem solar cell is increased from 1.93 to 1.99 V (certified 2.00 V), and a champion efficiency of 32.74% is achieved (certified 31.52%). This work demonstrates a molecular modification strategy to enhance the coordination activity of passivators, thereby achieving high‐performance perovskite/silicon tandem solar cells.