Morphological improvement of CH3NH3PbI3 films using blended solvents for perovskite solar cells

Perovskite solar cells with the structure of glass/florine-doped tin oxide (FTO)/electron transfer layer (ETL)/perovskite/hole transfer layer (HTL)/Ag were fabricated. The effects of blending solvents and thermal annealing on the surface morphology, structural, and optical properties of perovskite (CH3NH3PbI3) active layer were investigated. The active layer was optimized by adding 2-butanol (2-BTA) as an eco-friendly solvent into methyl ammonium iodide (MAI) solution used for spin coating on PbI2/(dimethylformamide (DMF)+dimethyl sulfoxide (DMSO)) film in the second step. The resulting morphology of CH3NH3PbI3 films was smooth and pinholes in the films were also reduced without change in the structure. The effects of thermal annealing on the surface morphology and structural properties of active layer were also studied. The fabricated device for the optimized condition showed the maximum power conversion efficiency (PCE) of ~8.6%.