Deprotonated Self-Assembled Monolayer for Inverted CsPbI₂Br Perovskite Solar Cells With Record-Efficiency and...

Owing to their unique molecular structures and outstanding optoelectronic properties, self-assembled monolayers (SAMs) hold enormous promise as hole-transport materials for p-i-n structured inorganic perovskite solar cells (IPSCs). However, weak interfacial adhesion and molecular aggregation lead to insufficient coating and easy peeling from the substrate, limiting the power conversion efficiency (PCE) and operational stability of IPSCs. This work employs KOH to deprotonate the ─PO₃H₂ of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) (2PACz-K), generating negatively charged ions, whose electrostatic repulsion suppresses intermolecular agglomeration, thereby forming a uniformly covered SAMs film. Meanwhile, 2PACz-K strengthens the binding interaction with the NiO_x substrate and generates robust chemical linkages, which effectively suppress interfacial separation and non-radiative recombination. Thus, in contrast to the control devices (15.13%), the inverted CsPbI₂Br IPSCs based on 2PACz-K delivered an optimal efficiency of 17.21% accompanied by a 1.326 V open-circuit voltage (V_OC), ranking among the highest values ever reported for such devices. Moreover, the deprotonated 2PACz-K alleviates acid-related corrosion toward the perovskite layer and passivates perovskite crystallites via K⁺ occupation at A-site defects. Under continuous maximum power point tracking (MPPT) at 85°C, devices incorporating 2PACz-K retained 80% of their initial performance over 710 h.