Unified Interface–Bulk Enhancements in Wide‐Bandgap Perovskites Enabled by Bifunctional Cyanoacetic Acid for Textured Silicon/Perovskite Tandem Solar Cells

ABSTRACT Wide‐bandgap (WBG) perovskite solar cells (PSCs) are essential for silicon/perovskite tandems but are hampered by buried‐interface disorder, bulk defects, and ion‐migration–induced degradation, challenges that are further amplified on textured silicon. We report a synergistic interface–bulk regulation strategy by incorporating cyanoacetic acid (CA) into both the self‐assembled monolayers (SAM) and the perovskite precursor. At the buried interface, CA anchors to substrate and interacts with SAM, forming a molecular bridge that suppresses SAM aggregation and homogenizes interfacial energetics. Within the perovskite, CA coordinates with undercoordinated Pb 2+ and stabilizes halides, producing uniform films with reduced trap densities. These enhancements strengthen the interface and suppress ion migration, nearly doubling the reverse‐bias breakdown voltage. The textured silicon/perovskite interface exhibits enhanced and more balanced interfacial electric fields across silicon pyramids. The optimized 1.66‐eV PSC achieves a steady‐state power conversion efficiency (PCE) of 24.43%, while integration into textured silicon tandem device yields a champion PCE of 32.43% with 93% retention after 1000 h.