Stabilizing perovskite precursors with the reductive natural amino acid for printable mesoscopic perovskite solar cells

Solution processability significantly advances the development of highly-efficient perovskite solar cells. However, the precursor solution tends to undergo irreversible degradation reactions, impairing the device performance and reproducibility. Here, we utilize a reductive natural amino acid, N-acetylcysteine (NALC), to stabilize the precursor solution for printable carbon-based hole-conductor-free mesoscopic perovskite solar cells. We find that I₂ can be generated in the aged solution containing methylammonium iodide (MAI) in an inert atmosphere and speed up the MA-FA⁺ (formamidinium) reaction which produces large-size cations and hinders the formation of perovskite phase. NALC effectively stabilizes the precursor via its sulfhydryl group which reduces I₂ back to I⁻ and provides H⁺. The NALC-stabilized precursor which is aged for 1440 h leads to devices with a power conversion efficiency equivalent to 98% of that for devices prepared with the fresh precursor. Furthermore, NALC improves the device power conversion efficiency from 16.16% to 18.41% along with enhanced stability under atmospheric conditions by modifying grain boundaries in perovskite films and reducing associated defects.