High-Quality Concentrated Precursor Solution in N,N-Dimethylformamide for Thick Methylammonium Triiodoplumbate Layer in Solar Cells

A high-quality precursor solution is essential for the fabrication of hybrid perovskite solar cells. This article reports a simple and efficient method for preparing a high-quality concentrated solution of methylammonium triiodoplumbate (MAPbI 3 ) in N, N -dimethylformamide (DMF) by using MAPbI 3 crystals instead of conventional lead iodine and methylammonium iodine blend. The MAPbI 3 concentration of the precursor solution is easily and accurately adjusted from 0 up to 1.64 M. An investigation of the dissolution process of the MAPbI 3 crystals reveals that the concentrated solution of MAPbI 3 in DMF is metastable, and the transition from the concentrated solution to solvated intermediate MAPbI 3 ·DMF determines the solubility of MAPbI 3 in DMF. The high purity and precise stoichiometric ratio of the crystals eliminate the possible impurities that initialize the transition to MAPbI 3 ·DMF and consequently suppress the transition and increase the stability of the concentrated solution. MAPbI 3 films with different thicknesses up to 800 nm are prepared with the conventional film fabrication technique, and the highest power conversion efficiency of 20.7% is achieved on corresponding solar cells. This newly developed method for preparing a concentrated precursor solution can be easily combined with other fabrication techniques for further development of industrial-scale manufacture of solar cells.