Amorphous Self-Assembled Molecule with Distorted Backbone Suppresses Aggregation for Highly Efficient Inverted Perovskite Solar Cells

Abstract

Self-assembled molecules (SAMs) commonly employed in inverted perovskite solar cells (PSCs) are plagued by severe molecular aggregation that leads to non-uniform substrate coverage, consequently increased interfacial charge recombination and compromised operational stability. To overcome this limitation, we rationally design a novel SAM, (4-(2,7-bis(4-methoxyphenyl)-9,9-dimethylacridin-10(9H)-yl)butyl)phosphonic acid (MeO-PhAPA), featuring a structurally distorted backbone. The core structure of MeO-PhAPA integrates an sp3-hybridized carbon atom bonded to two methyl groups, which imposes pronounced molecular distortion that breaks molecular planarity and effectively suppresses deleterious π-π stacking. Additionally, the single-bond-linked two methoxyphenyl substituents further increase steric hindrance. This tailored molecular design robustly suppresses intermolecular aggregation of MeO-PhAPA, favoring the formation of a uniform, well-wetted amorphous thin film. Concurrently, MeO-PhAPA optimizes interfacial energy level alignment and delivers superior hole-extraction capability. Moreover, compared with the conventional MeO-4PACZ SAM, MeO-PhAPA facilitates the growth of high-quality perovskite films with larger grain sizes, lower defect density, and reduced bulk residual stress. Consequently, inverted PSCs incorporating MeO-PhAPA achieve a champion power conversion efficiency of 26.85% (certified 26.62%), markedly outperforming the control device based on MeO-4PACZ (24.12%). The optimized devices also demonstrate substantially enhanced stability under prolonged operational and thermal stresses.