Guanidyl‐Engineered SAMs with Electrostatic–Coordination Synergy for High‐Efficiency Tandem‐Compatible Perovskite Solar Cells

ABSTRACT Wide‐bandgap inverted perovskite solar cells (PSCs) have attracted significant interest owing to their excellent stability feature and unique compatibility with tandem device architectures. However, two major challenges remain: the inhomogeneity of self‐assembled monolayers (SAMs) and the insufficient passivation of buried interface defects. In this study, we introduce polyhexamethylene guanidine hydrochloride (PHMG) as an additive to 4‐(7H‐dibenzo[c,g]carbazole‐7‐yl) phosphonic acid (4PADCB) SAMs, wherein guanidyl groups in PHMG establish electrostatic–coordination synergy with 4PADCB and perovskite species, respectively. The electrostatic interaction suppresses SAM aggregation, reduces interfacial defects, and optimizes energy‐level alignment at the SAM/perovskite interface, while the coordination effect promotes perovskite crystallization, enlarges grains, reduces defect densities, and relaxes interface stress. Consequently, the optimized 1.68 eV‐bandgap PSC delivers a remarkable power conversion efficiency (PCE) of 23.62%, representing the highest value reported to date, with over 95% efficiency retention after 1300 h of thermal aging at 85°C in N 2 . Furthermore, these PSCs are integrated into perovskite/silicon tandem solar cells, achieving a record PCE of 32.49% for a laminated tandem device and the superior values of 32.25% (with an active area of 1 cm 2 ) and 29.34% (with an active area of 20 cm 2 ) for monolithic tandem devices.