Tailoring Molecular‐Scale Contact at the Perovskite/Polymeric Hole‐Transporting Material Interface for Efficient Solar Cells

Abstract Perovskite solar cells (PSCs) have delivered a power conversion efficiency (PCE) of more than 25% and incorporating polymers as hole‐transporting layers (HTLs) can further enhance the stability of devices toward the goal of commercialization. Among the various polymeric hole‐transporting materials, poly(triaryl amine) (PTAA) is one of the promising HTL candidates with good stability; however, the hydrophobicity of PTAA causes problematic interfacial contact with the perovskite, limiting the device performance. Using molecular side‐chain engineering, a uniform 2D perovskite interlayer with conjugated ligands, between 3D perovskites and PTAA is successfully constructed. Further, employing conjugated ligands as cohesive elements, perovskite/PTAA interfacial adhesion is significantly improved. As a result, the thin and lateral extended 2D/3D heterostructure enables as‐fabricated PTAA‐based PSCs to achieve a PCE of 23.7%, improved from the 18% of reference devices. Owing to the increased ion‐migration energy barrier and conformal 2D coating, unencapsulated devices with the new ligands exhibit both superior thermal stability under 60 °C heating and moisture stability in ambient conditions.