Deprotonation‐Resistant Bimolecular Passivation Strategy for 26% Efficient and Stable Inverted Perovskite Solar Cells

Abstract Surface passivation has significantly increased the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, the most advanced methods of surface passivation depend on ammonium ligands that can lose protons under light and heat. Here, a dual‐molecule approach for surface passivation is presented by combining 4‐methylpyridine‐3‐sulfonic acid (MPSA) with ethanolamine hydrochloride (EOACl). The sulfonic acid group of MPSA provides additional protons and thus prevents the loss of protons from ammonium cations. This method reduces the deprotonation equilibrium constant of the ligands by more than 10‐fold. At the same time, EOA⁺, with its strong molecular dipole (6.72 D) and high adsorption energy (Δ E = −2.68 eV), exhibits excellent field effect and chemical passivation. The enhanced perovskite solar cells achieved a PCE of 26.04%, with the encapsulated devices retaining 91.2% of their original PCE after 1100 h of MPPT operation. After 800 h of thermal aging in a dark, inert atmosphere at 85 °C, the efficiency also remained at 90.3%, showing much improved stability for practical applications.