Efficient planar perovskite solar cells with large fill factor and excellent stability

The quality and stability of perovskite films are critical for solar cells using this technology. Here, we fabricate a high-quality CH 3 NH 3 PbI 3 perovskite film by introducing small amounts of N -methyl-2-pyrrolidone into a mixture of γ-butyrolactone and dimethylsulphoxide. The perovskite film consists of compact grains (average sizes of ∼57 nm) with unclear boundaries which show a mirror-like surface with the root mean square roughness of only 2.39 nm. The power conversion efficiency of 11.77% is obtained with the fill factor as high as 80.52% under one sun illumination (100 mW cm −2 ). Furthermore, the stability of the perovskite solar cells is greatly improved by forming compact perovskite films with excellent surfaces. The results indicate that high-quality perovskite films with compact grains are a promising choice for high-stable, efficient perovskite solar cells.