Solvent‐Additive Synergy Optimizes the Performance of Methylamine‐Based Printable Mesoscopic Perovskite Solar Cells

Printable mesoporous perovskite solar cells (p‐MPSCs) are promising for commercialization due to their outstanding stability and low‐cost manufacturing process. However, their performance is being limited by high nonradiative energy losses. One effective approach to reducing these losses is to precisely control the crystallization kinetics of perovskite within the mesoporous scaffold to obtain high‐quality films. In this work, we introduce rubidium chloride (RbCl) as an additive into a 2‐methoxyethanol/ N , N ‐dimethylacetamide (2‐ME/DMAc) binary solvent system to regulate the phase transformation of MAPbI ₃ . The weak solvent–perovskite interaction in this system promotes direct crystallization and suppresses nonphotoactive phases. Furthermore, RbCl stabilizes this interaction, optimizing the crystallization pathway. This strategy produces perovskite films with high crystallinity and low defect density in mesoporous structures, effectively reducing nonradiative losses. The resulting carbon‐based p‐MPSCs fabricated at room temperature achieve a power conversion efficiency (PCE) of 18.48%, exhibit negligible degradation during 300 s of steady‐state output, and retain 95% of initial PCE after 120 days of storage under ambient conditions (25 ± 5°C, ≈50% RH).