Bifunctional Interface Synergy for High-Performance Wide-Bandgap and Tandem Perovskite Solar Cells

Wide-bandgap (WBG) perovskite solar cells are essential for high-efficiency all-perovskite tandem solar cells, yet interfacial defects and poor energy level alignment in WBG sub-cells limit their performance. Here, we report a homogenized bifunctional interface modification strategy by integrating sulfaguanidine (SG) and 1,3-diaminopropane dihydroiodide (PDAI₂). SG forms a stable cross-hybrid network via coordination with under coordinated Pb²⁺ and hydrogen bonding with surface iodide, effectively suppressing non-radiative recombination and stabilizing Pb-I octahedra, while PDAI₂ further enhances charge extraction through dipole-induced band offset. This synergistic modification enables inverted 1.77 eV perovskite solar cells with a champion efficiency of 20.27%, and reduced open-circuit voltage loss (0.42 V). Unencapsulated devices retain 94% of their initial efficiency after 800 hours, demonstrating excellent stability. Crucially, an all-perovskite tandem solar cell based on this top cell achieves a remarkable efficiency of 28.14%. This bifunctional strategy offers an effective approach to minimizing interfacial loss issues, providing a critical foundation to the development of perovskite tandem photovoltaics.