Solvent engineering of spin-coating solutions for planar-structured high-efficiency perovskite solar cells

Control of the morphology and coverage of high-quality perovskite films is the main issue affecting planar-structured perovskite solar cells fabricated by solution processing. In this work, the solvent engineering of mixed solutions for spin-coating uniform perovskite thin films was investigated in detail by adding different ratios of N,N -dimethylformamide (DMF) or γ-butyrolactone (GBL) to dimethyl sulfoxide (DMSO). The morphology and film thickness of the resulting perovskite films were found to be significantly altered. At 20%~40% (volume fraction) of N , N -dimethylformamide mixed with DMSO, micrometer scale grains and reduced grain boundaries were observed on the highly uniform perovskite thin films. The optimized planar-structured perovskite solar cells showed power conversion efficiency as high as 16.5% and a stabilized efficiency of 14.4% at a fixed forward bias of 0.88 V.