Suppressing morphological and energetic disorder in self-assembled interfaces for efficient inverted perovskite solar cells

Self-assembled monolayers (SAMs) serve as key hole-transport layers in inverted perovskite solar cells (PSCs), however conventional SAMs often form nonuniform films and introduce interfacial defects. Although spiro-structured SAMs have been shown to improve film homogeneity through steric hindrance, the influence of molecular disorder on interfacial energetics and charge transport remains insufficiently understood. Here, we explore how morphological and energetic disorder in spiro-based SAMs modulate interfacial charge-transfer processes and device performance. We design a series of SAMs featuring either a freely rotatable benzene substituent (Dip-4PACz) or conformationally “locked” aromatic frameworks (Flu-4PACz and Xan-4PACz) to systematically regulate molecular freedom. Our results show that rotational disorder enhances excited-state energy dissipation during charge transport, thereby limiting device efficiency. In contrast, morphologically and energetically ordered SAMs optimize energy-level alignment, improve perovskite film quality, and facilitate charge extraction, thereby suppressing interfacial nonradiative recombination and reducing energetic losses. Consequently, PSCs based on Flu-4PACz and Xan-4PACz achieve power conversion efficiencies of up to ∼25.8%.