Synergistic Hole‐Selective Contact Enabling Highly Efficient Perovskite/Organic Tandem Solar Cells

ABSTRACT Efficiency improvements in organic solar cells (OSCs), perovskite solar cells (PSCs), and tandem solar cells (TSCs) critically depend on optimized hole‐selective interfacial contacts. Co‐assembled self‐assembled monolayers (co‐SAMs) offer an effective route to enhance hole extraction. However, their practical design is limited by the absence of universal material selection rules, often leading to incompatible molecular packing and suboptimal interfaces. Here, we propose a synergistic co‐SAM strategy that enables high‐quality hole‐selective contacts across OSCs, PSCs, and TSCs. By co‐assembling carbazole‐based phosphonic acids with chain length‐matched phosphonic acid derivatives, we reveal that rational molecular pairing governs the synergistic behavior of co‐adsorbates. PAC 2 Br shows optimal compatibility with 2PACz, while PAC 4 Br matches well with 4PACz, resulting in homogeneous molecular distribution, compact surface coverage, and favorable energy‐level alignment. These synergistic interfaces effectively suppress interfacial recombination and enhance charge extraction. Consequently, co‐SAM‐modified devices achieve power conversion efficiencies of 19.60% in OSCs. Demonstrating the universality of the co‐SAM strategy, the co‐SAM pairing yields PSCs with efficiencies up to 25.78%, and further enables a champion PCE of 26.06% for perovskite/organic TSCs. This work establishes synergistic co‐SAMs as a general and effective interfacial design principle for high‐efficiency photovoltaic devices.