Molecular Bridging at Buried Interface Enables Efficient Wide‐Bandgap Perovskite Solar Cells

Abstract The regulation of buried interface is crucial for high‐performance wide‐bandgap perovskite solar cells (PSCs), which can influence the interfacial defects, the charge transport, and the crystallization of perovskites. In this work, a facile strategy is reported of inserting a multi‐functional (Z)‐4‐Fluoro‐ N ′‐hydroxybenzimidamide (4F‐HBM) molecule between self‐assembled monolayer (SAM) and wide‐bandgap (WBG) perovskite layer, actively regulating crystal growth and promoting hole extraction. It is found that the F atoms in 4F‐HBM form a hydrogen bond with the SAM. 4F‐HBM interacts with Pb 2+ in the perovskites, effectively reducing the defect state density at the interface and non‐radiative charge recombination losses at the buried interface. The 1.77‐eV WBG PSC using 4F‐HBM has a significantly improved power conversion efficiency of 20.09% and a high fill factor of 84.71%, higher than those for the control device (18.47% and 82.53%, respectively). The device can maintain 85% of its original efficiency after 821 h of maximum power point tracking, showing improved stability. Four‐terminal all‐perovskite tandem solar cells by combining such a semitransparent WBG subcell with a 1.25 eV low‐bandgap PSC obtains a PCE of 28.71%, among the highest efficiencies for four‐terminal all‐perovskite tandem cells to date. The work offers a promising strategy to enhance buried interface contact and defect passivation for perovskite‐based tandem devices.