Synergy of Low- and High-Polarity Cations for Stabilizing 2D Perovskites.

Perovskite solar cells (PSCs) employing three-dimensional/two-dimensional (3D/2D) heterostructures achieve high efficiencies but suffer from limited operational stability. Combining high-throughput experiments with first-principles simulations, we unveil that 2D perovskites are intrinsically susceptible to thermal degradation due to the deprotonation of spacer cations and subsequent escape of hydrogen iodide. Through artificial intelligence analysis of 278 distinct perovskites, we identify the surface electrostatic properties and molecular polarity of spacer cations as the key descriptors governing thermal resilience. Finally, we discover a bi-cationic 2D perovskite that integrates low-polarity phenylethylammonium with high-polarity pentafluorophenylethylammonium (5FBA), synergistically resolving phase segregation and thermal degradation beyond what either cation can achieve alone. The bi-cationic 3D/2D perovskite film stack shows suppressed ion migration owing to the robust interaction between 5FBA and 3D perovskite. Consequently, the resulting PSCs retain over 92% of their initial efficiency after 1500 h of thermal aging at 85°C and over 90% after 2000 h of continuous operation under 1-Sun illumination.