Homogeneous permeation and oriented crystallization in nanostructured mesopores for efficient and stable printable mesoscopic perovskite solar cells

The low-cost and scalable printable mesoporous perovskite solar cells (p-MPSCs) face significant challenges in regulating perovskite crystal growth due to their nanoscale mesoporous scaffold structure, which limits the improvement of device power conversion efficiency (PCE). In particular, the most commonly used solvents, N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), have a single chemical interaction with the precursor components and high volatility, which is insufficient to self-regulate the perovskite crystallization process, leading to explosive nucleation and limited growth within mesoporous scaffolds. Here, we report a mixed solvent system composed of methylamine formaldehyde (MAFa)-based ionic liquid and acetonitrile (ACN) with the strong C=O–Pb coordination and N–H⋯I hydrogen bonding with perovskite components. We found that the mixed solvent system is beneficial for the precursor solution to homogeneously penetrate into the mesoporous scaffold, and the strong C=O–Pb coordination and N–H⋯I hydrogen bonding interaction can promote the oriented growth of perovskite crystals. This synergistic effect increased the PCE of the p-MPSCs from 17.50% to 19.21%, which is one of the highest records for p-MPSC in recent years. Additionally, the devices exhibit positive environmental stability, retaining over 90% of the original PCE after 1,200 h of aging under AM 1.5 illumination conditions at 55 °C and 55% humidity.