Hydrophobic coating over a CH3NH3PbI3 absorbing layer towards air stable perovskite solar cells

Lead halide perovskite solar cells with high efficiency have recently attracted tremendous attention. However, the poor stability of perovskite materials has hindered their practical applications. Here, we presented a hydrophobic agent, fluoroalkyl silane, to modify both the light absorbing layer and the hole transport layer. In the presence of a hydrophobic coating, we obtained a stable perovskite solar cell with less hysteresis between the forward sweep and the reverse sweep in air. The effect of fluoroalkyl silane concentration on the stability was investigated; with an optimized 2.0 wt% fluoroalkyl silane solution treatment, the efficiency of perovskite solar cells has reached over 12.0 +/- 0.4%. Moreover, for those perovskite solar cells that are exposed to air with about 50% relative humidity, the efficiency was maintained at around 12% for a duration of more than 500 h, while the efficiency of those without hydrophobic coating sharply decreased from about 12% to 1% in a duration of 250 h.