Crystallization Control Assists Annealing‐Free Fabrication of Printable Mesoscopic Perovskite Solar Cells with Power Conversion Efficiency over 17%

The one‐step drop‐casting for preparing perovskite films in three‐layer mesoporous for printable mesoscopic perovskite solar cells always results in insufficient filling of mesopores. A binary solvent based on 2‐methoxyethanol (2‐ME) and 1‐methyl‐2‐pyrrolidone (NMP) offers a method suitable for annealing‐free to prepare dense perovskite films in mesopores. The crystallization process of perovskite films in mesopores can be adjusted by the content of NMP in the solvent. The introduction of NMP enhances the density of the perovskite film based on the binary solvent system, optimizing the contact between the perovskite film and the mesoporous scaffold. When the ratio of 2‐ME to NMP is 9:1, the optimal device achieves impressive performance metrics, including a power conversion efficiency (PCE) of 17.28%, an open‐circuit voltage of 0.98 V, a short‐circuit current of 23.80 mA cm −2 , and a fill factor of 74.08%. This represents the highest PCE achieved to date in the annealing‐free preparation of perovskite films for printable mesoscopic perovskite solar cells. Furthermore, devices based on this binary solvent system exhibit remarkable stability, with almost no loss in efficiency even after 120 days of storage in an air environment without encapsulation.