Effects of mixed solvent on morphology of CH3NH3PbI3 absorption layers and photovoltaic performance of perovskite solar cells

In this paper, a two-step method is used to prepare a high-quality CH 3 NH 3 PbI 3 layer for carbon-based hole conductor-free perovskite solar cells (PSCs). In the first step, the solvent for the PbI 2 /DMF solution is changed to a mixed solvent of N,N -dimethylformamide (DMF) with dimethyl sulfoxide (DMSO) from pure DMF solvent. This process requires 3.5 h for PbI 2 films deposited from the PbI 2 /DMF solution to completely convert to perovskite in a methyl amine iodide (MAI)/iso-propyl alcohol (IPA) solution, and perovskite films have a rough surface with a few large crystals. This mixed solvent accelerates the conversion of PbI 2 to CH 3 NH 3 PbI 3 , resulting in smooth CH 3 NH 3 PbI 3 films without residual PbI 2 . Only 15 min are required for PbI 2 films to completely convert to perovskite when the volume ratio of DMSO to DMF is 1:4. As a result, the photovoltaic performance, especially on the fill factor (FF) of PSCs fabricated from DMF/DMSO solvent, improved mainly due to the better contact of perovskite/carbon interface and faster charge transport of the perovskite layer.