Pre-assembly-co-anchoring strategy enabling high-coverage SAMs and buried interface passivation for inverted perovskite solar cells

The performance of perovskite solar cells (PSCs) is highly dependent on the quality of the hole transport layer (HTL). However, conventional carbazole-based self-assembled monolayers (SAMs) exhibit weak interactions with the NiO_x substrate and are prone to molecular self-aggregation, resulting in low surface coverage and poor interfacial contact, which in turn cause severe non-radiative recombination losses. Here, we propose the “pre-assembly-co-anchoring” strategy, which is achieved by rationally designing a multifunctional co-assembling molecule, 3-(trifluoromethyl) benzoic acid (TFPA). The conjugated structure of TFPA acts as a molecular spacer to disperse the MeO-2PACz molecules through π-π stacking, while the carboxyl groups help to anchor them onto the NiO_x substrate, thereby forming a dense and solvent-resistant SAM layer. The –CF₃ terminal group simultaneously passivates the buried interface defects of the perovskite (PVK) through the Pb–F bond and stabilizes the FA⁺ cation through N–H···F hydrogen bonding. This pre-assembled and re-anchored design eliminates interface composite centers, optimizes energy level arrangement to enhance hole extraction, and inhibits non-radiative recombination. Therefore, this strategy results in a p-i-n device with a power conversion efficiency (PCE) of 25.7% and improved stability. This study indicates that, in photovoltaic devices, it is equally important to actively regulate the molecular assembly behavior and optimize the interface connection to achieve high performance.