Efficient planar perovskite solar cells based on high-quality perovskite films with smooth surface and large crystal grains fabricated in ambient air conditions

Due to the hygroscopic feature of methylammonium component, it is still a big challenge to prepare efficient perovskite solar cells in ambient air conditions with high relative humidity about 60-80%. In the humid air conditions, it can only obtain the network-like PbI2 films and porous perovskite films with poor surface morphology when utilizing the typical two-step method and usually used precursor solution. Because of the key role of the morphology of PbI2 films in determining the final quality of perovskite films, the first challege is to fabricate high-quality PbI2 films. Later, another challege is how to eliminate the influence of moist air when converting PbI2 films into perovskite films. For overcoming the challenges, a special additive of n-butyl amine is used to prepare full coverage and continuous PbI2 films, and then a low-hydrophilic n-butanol solvent and a novel multi-cycle short-time dipping reaction are used to successfully convert these PbI2 films into high-quality perovskite films with smooth surface and large crystal grains similar as that of the ones prepared with one-step anti-solvent method in glove box. The best performance device based on the high-quality perovskite film achieves an average power conversion efficiency (average of the forward and reverse scans) of 17.56% with slight hysterisis and good reproducibility.