Dual‐Interface Modification for Inverted Methylammonium‐Free Perovskite Solar Cells of 25.35% Efficiency with Balanced Crystallization

Abstract In a methylammonium‐free (MA‐free) composition, the uncontrollable crystallization process between Cs and formamidine (FA) currently hinders its efficiency enhancement, especially in inverted perovskite solar cells (PSCs). Here, a dual‐interface modification of perovskite films is proposed by simultaneously introducing additives and surface passivators. In particular, (aminomethyl)phosphonic acid (AMP) is introduced into the precursor solution to balance crystallization by inducing the preferential crystallization of FA through the specific formation of strong hydrogen bonds with FA. In addition, AMP spontaneously sinks and anchors to the buried interface to fill the voids of the self‐assembled monolayer (SAM) via the covalent bonds formed by ─PO₃H₂ and FTO. Subsequently, by the sequential modification of perovskite surface with 2‐(3‐fluorophenyl)ethylamine iodide (mF‐PEAI) and piperazine diiodide (PDI), a uniform surface potential is achieved and recombination losses at the interface are minimized. Notably, the dual‐interface‐modified inverted MA‐free PSCs achieve a state‐of‐the‐art power conversion efficiency (PCE) of 25.35% (certified: 24.87%) with a satisfactory V_oc of 1.17 V based on the bandgap of 1.52 eV. Importantly, the unencapsulated devices maintain 92.8% and 91.7% of the initial efficiency after 1000 h of maximum power output (MPP) tracking and >800 h of heating at 85 °C, respectively, confirming excellent operational and thermal stability.