Molecular Conjugation Strategy for Highly Efficient and Stable Inverted Wide‐Bandgap Perovskite Solar Cells

The buried interface between the hole‐transport layer and the perovskite absorber is critical for the performance and stability of wide‐bandgap perovskite solar cells (PSCs). This work reports two novel self‐assembled monolayer (SAM) hole‐transport materials, MeS‐4PACz (with a flexible alkyl chain linker) and MeS‐ρPACz (with a rigid phenyl ring linker), designed to engineer this key interface. Theoretical and experimental analyses reveal that the planar conjugated phenyl linker in MeS‐ρPACz significantly enhances molecular rigidity, thermal stability, packing density, and dipole alignment compared to its alkyl‐chain counterpart. This superior molecular configuration promotes a denser and more ordered SAM, which facilitates the growth of high‐quality perovskite films with larger grains, improved crystallinity, and reduced defect density. Consequently, devices incorporating the MeS‐ρPACz SAM exhibit more efficient hole extraction, suppressed non‐radiative recombination, and optimal energy level alignment. The resulting inverted PSCs achieve a champion power conversion efficiency (PCE) of 23.30% with negligible hysteresis, outperforming MeS‐4PACz‐based devices (22.38%). More importantly, unencapsulated MeS‐ρPACz‐based PSCs retain over 90% of their initial PCE after 2000 h in a nitrogen atmosphere, demonstrating significantly enhanced operational stability. This study highlights the pivotal role of molecular rigidity and conjugated linkers in SAM design for developing highly efficient and stable wide‐bandgap PSCs.