Controllable intermediates by molecular self-assembly for optimizing the fabrication of large-grain perovskite films via one-step spin-coating

In the past two years, the introduction of dimethylsulfoxide (DMSO) has recognized as an effective way to prepare high-quality pervoskite films. During the developed DMSO process, the formation of an intermediate phase has proven to uniform crystal growth rates between CH3NH3I (MAI) and PbI2 in common solvents. In this work, controllable intermediates were obtained in dimethylformamide (DMF) by additional solvent of DMSO, which tend to be closely packed by means of intermolecular self-assembly. In addition, the bond strength and chemical composition of intermediate phase were investigated with FTIR and TGA. The use of different ratios of DMSO leads to four different complexes of MAI·PbI2·DMF and MAI·PbI2·(DMSO)y (y = 0.6, 1.5, 1.9), thus dramatically influencing the crystallization of perovskite films. Of these complexes, optimized MAI·PbI2·(DMSO)1.5 intermediate adduct enables highly dense perovskite thin films with large grain size and enhances efficient perovskite solar cells with high charge carrier lifetime. [Display omitted] •Controllable MAI·PbI2·(DMSO)y adducts were first found via One-Step Spin-Coating.•The controllable morphology of MAPbI3 thin films were obtained.•By optimizing intermediate adduct, a PCE of 16.41% is achieved.