High-quality Concentrated Precursor Solution in N,N-dimethylformamide for Thick Methylammonium Triiodoplumbate Layer in Solar Cells.

: High-quality precursor solution is essential for the fabrication of hybrid perovskite solar cells. This paper reports a simple and efficient method of preparing the high-quality concentrated solution of methylammonium triiodoplumbate (MAPbI3) in N,N-dimethyl formamide (DMF) by using MAPbI3 crystal instead of conventional lead iodine and methylammonium iodine blend. The MAPbI3 concentration of the precursor solution is easily and accurately adjusted from zero up to 1.64 M. The investigation on the dissolution process of the MAPbI3 crystal reveals that the concentrated solution of MAPbI3 in DMF is metastable, and transition from the concentrated solution to solvated intermediate MAPbI3∙DMF determines the solubility of MAPbI3 in DMF. The high purity and precise stoichiometric ratio of the crystal eliminate the possible impurities that initialize the transition to MAPbI3∙DMF, and consequently suppress the transition and increase the stability of the concentrated solution. MAPbI3 films with different thickness up to 800 nm are prepared with conventional film fabrication technique, and a highest power conversion efficiency of 20.7% is achieved on corresponding solar cells. The newly developed method to prepare the concentrated precursor solution can be easily combined with other fabrication techniques for the further development of industrial-scale manufacture of solar cells.