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

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 N₂. 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 cm²) and 29.34% (with an active area of 20 cm²) for monolithic tandem devices.