Perovskite solar cells (PSCs), due to their outstanding photovoltaic properties, simple and low-cost solution fabrication process, abundant precursors, and skyrocketing power conversion efficiency (PCE), have attracted tremendous attention and show great promise for scale-up and future commercialization. While the unprecedentedly high efficiency using perovskites is an astonishing achievement, issues relating to the long-term durability against atmospheric moisture and oxygen, heat, and light still raise concerns for the successful commercial application of PSC technology. The most effective devices employ acidic self-assembled monolayers (SAMs) of organic small molecules that are capable of binding metal oxide contacts, resulting in inverted PSCs with improved efficiency. Such molecularly thin SAMs offer numerous potential advantages, such as the need for tiny amounts of material, and tunable chemistry to obtain cheap but efficient semiconductors that enable additional functionalities and further device performance improvements. However, further spread of such materials is hindered by the rather poor coverage, dewetting of the perovskite precursor solution, due to the nonpolar SAM surface, and stability issues due to acidic SAM-favored corrosion of contacts.

Despite the central role of SAMs in PSCs, their molecular design paradigm has remained essentially unchanged since it was discovered. Nearly all reported SAMs rely on intrinsically acidic anchoring groups, resulting in interfacial inhomogeneity, insufficient charge extraction, and poor operational stability—issues that fundamentally constrain the long-term performance and manufacturability of PSCs.

This work disrupts this long-standing design bottleneck. We introduce an entirely new class of alkali metal–based ionic phosphonate salt SAMs (2PACz-M)—the first demonstration of SAM formation directly from ionic salt solutions. Through targeted head-group neutralization of the benchmark 2PACz molecule, we transform acidic SAMs into non-acidic, highly delocalized, electronically active ionic interfaces. This departure from conventional SAM chemistry offers several breakthrough advantages: non-acidic, neutral SAMs for PSCs eliminate acid-induced corrosion and dramatically improve interfacial uniformity and electronic coupling; the first demonstration of ionic phosphonate SAMs assembled from aqueous-compatible salt solutions enables green-solvent processing and vastly improves compatibility with perovskite inks. These innovations translate directly into record-level device performance: 1.55 eV PSCs achieve a certified PCE of 26.88% and a FF of 86.57%, and a 29.7 cm² module delivers 23.32%, the highest among SAM-based modules.

Beyond performance, the conceptual shift—from acidic molecular anchoring to ionic, electronically delocalized SAMs—establishes a new direction for interfacial engineering in perovskite photovoltaics. This molecular design framework is generic, scalable, and applicable across diverse bandgaps, device architectures, and fabrication environments.