Meta-Fluorinated Phenyl-Linkers Enable a Compact Self-Assembled Monolayer for Efficient and Stable Inverted Perovskite Solar Cells

As a crucial interfacial engineering strategy for inverted perovskite solar cells (PSCs), the development of high-density and well-ordered self-assembled monolayer (SAM) is essential to achieve photovoltaic devices with both high efficiency and long-term stability. Herein, we report three SAM materials ( Z01, Z01-of, Z01-mf ) comprising a phenoxazine headgroup and a carboxylic acid anchoring group, connected by phenyl, ortho-fluorinated phenyl, and meta-fluorinated phenyl spacers, respectively. Compared to Z01 and Z01-of, Z01-mf exhibits relatively higher molecular planarity and lower highest occupied molecular orbital energy level. Additionally, the fluorine substituent in Z01-mf reduces the electron density on the carbonyl oxygen of the carboxyl anchoring group, thus weakening intermolecular hydrogen bonding. The combination of weakened hydrogen bonding and strengthened molecular planarity facilitates the formation of a more compact molecular packing on indium tin oxide substrates. The favorable self-assembly of Z01-mf enables more efficient hole extraction and suppresses non-radiative recombination losses, thereby yielding simultaneous improvements in open-circuit voltage and fill factor. As a result, the fill factor of inverted PSCs based on Z01-mf reaches 84.43%, outperforming those with Z01-of (81.79%) and Z01 (81.74%).