A mixed solvent for rapid fabrication of large-area methylammonium lead iodide layers by one-step coating at room temperature

A simple and reliable method of preparing high-quality perovskite layers is essential for the high photovoltaic performance of perovskite solar cells. Here, a new low-boiling-point solvent system composed of methylamine solution in ethanol and tetrahydrofuran is designed for methylammonium lead iodide precursor solutions. Concentrated methylammonium lead iodide precursor solutions with a concentration of 2.1 M are obtained, and smooth and compact methylammonium lead iodide films with an area of up to 600 cm2 are prepared directly by one-step spin-coating or blade-coating the precursor solution at room temperature. The rapid evaporation of the solvent and strong interaction between methylamine and methylammonium lead iodide lead to a high crystal nucleus density and intermediate-free crystallization path, and consequently result in a compact and smooth film. The high-quality methylammonium lead iodide films show excellent photovoltaic performance in conventional mesoporous solar cells with efficiencies of 20.0% (0.1 cm2) and 15.6% (10 cm2). Because of the low cost and ease of operation, the solvent system developed in this work is promising both in the laboratory and for future industrialization.