Backbone isomerism in carbazole self-assembled monolayers enables uniform and stable NiOx interfaces for inverted perovskite solar cells.

Carbazole-based self-assembled monolayers (SAMs) are widely used to modify NiOx contacts in inverted perovskite solar cells (PSCs), yet the role of π-backbone isomerism in regulating SAM assembly behavior, coverage, and buried-interface robustness remains underexplored. Here, we design a set of 3PACz-derived carbazole SAMs with identical phosphonic-acid anchors and C3 alkyl spacers but distinct π-conjugated backbones to isolate the effect of backbone geometry. Compared with non-extended 3PACz and linearly π-extended F-3PADCz, the bent constitutional isomer I-3PADCz exhibits the weakest self-aggregation tendency while maintaining the strongest NiOx anchoring and a favorable interfacial dipole. This molecular configuration enables a dense, solvent-robust, and electronically homogeneous SAM contact, thereby promoting uniform perovskite crystallization, reducing residual strain, and yielding a compact buried-interface morphology with fewer defects. Consequently, I-3PADCz-based inverted PSCs achieve a champion power conversion efficiency of 25.44% and retain 97% of their initial efficiency after 646 h of continuous 1 sun maximum power point tracking under the ISOS-L-1 protocol. I-3PADCz also delivers efficiencies of 25.40% in blade-coated FAPbI3 small-area devices and 23.46% in 6.25 cm2 mini-modules. This work establishes π-backbone isomerism as an effective strategy for robust and scalable NiOx/SAM contacts.