Strengthening Substrate Anchoring of Polymeric Self‐Assembled Monolayers for Efficient and Stable Inverted Perovskite Solar Cells

ABSTRACT Small‐molecule‐based self‐assembled monolayers (SAMs) used as hole‐transporting layers have achieved exceptional efficiencies in inverted perovskite solar cells (PSCs). However, inadequate substrate coverage and insufficient operational stability of small molecules have led to the development of polymeric SAMs as an alternative. Nevertheless, the molecular configuration of polymeric SAMs remains underexplored, resulting in lower performance compared to small‐molecule SAMs. Here, our results show that the previously reported Poly‐4PACz contains linkage sites generating significant steric repulsion between monomers, forcing phosphate groups into an alternative alignment and reducing substrate anchoring capability. Inspired by this, we designed a new polymeric SAM, Poly‐4PADCB, by selecting specific monomer linkage sites to reduce steric hindrance. Consequently, the alignment of phosphate groups in Poly‐4PADCB becomes unidirectional after polymerization, resulting in higher coverage and improved molecular ordering. This ordered template facilitates high‐quality perovskite growth and optimizes energy level alignment at the buried interface via a synergistic dipole superposition effect. Ultimately, PSCs based on Poly‐4PADCB achieve a power conversion efficiency (PCE) of 26.90% (certified 26.50%) and a large‐area (1 cm 2 ) PCE of 25.54% (certified 25.19%). This robust interfacial architecture inhibits SAM desorption and diffusion, with 96% of initial performance retained after 2000 h of continuous maximum power point tracking under the ISOS‐L‐2 protocol.