High‐Performance Inverted Perovskite Solar Cells Enhanced via Partial Replacement of Dimethyl Sulfoxide with N‐Methyl‐2‐Pyrrolidinone

Herein, a very simple but efficient method is developed to concurrently improve the quality of perovskite film and enhance the interfaces of perovskite solar cells (PSCs) concurrently via partially replacing dimethyl sulfoxide (DMSO) with N‐methyl‐2‐pyrrolidinone (NMP) in inverted planar PSCs. With the systematic investigations, it is found that the perovskite films fabricated with this simple method demonstrate higher crystallinity, larger grain size with less grain boundaries, and better perovskite–substrate interface with very rare voids. All of these lead to efficient all‐round defects suppression and high performance of the corresponding PSCs. As a result, the tri‐mixed solvent (DMF:DMSO:NMP = 4:0.75:0.25) processing renders a power conversion efficiency (PCE) of 21.53%, which is much higher than that of PSCs fabricated with traditional bi‐mixed solvent (DMF:DMSO = 4:1) (only 17.05%). Notably, the simple‐method‐fabricated PSCs demonstrate remarkable humidity and thermal stabilities even without any encapsulation (90.6% and 75.2% of initial PCE are retained after more than 511 h in air with relative humidity (RH) ≈ 50% at room temperature and 216 h in air with RH 70% at continuous heating of 70 °C, respectively). All these results demonstrate that the simple method by partially replacing DMSO with NMP is very efficient to improve the quality of perovskite layer and yield high‐performance PSCs.