Highly efficient and stable perovskite solar cell prepared from an in situ pre-wetted PbI2 nano-sheet array film

Due to its good pore-filling and morphology control, a two-step deposition technique has been widely used in perovskite film preparation. However, the initial PbI2 film used for the two-step deposition method is usually dense, crystalline and layered, leading to a poor quality perovskite film with a certain amount of PbI2 residue, thus resulting in an inferior stability and low power conversion efficiency (PCE) of the device. In this work, we developed an in situ pre-wetted PbI2 nano-sheet array film to achieve high-quality CH3NH3PbI3 (MAPbI3) perovskite films via a two-step deposition method. By introducing a small amount of hydrogen chloride isopropanol solution (IPA HCl) into the PbI2 precursor solution, an in situ pre-wetted PbI2 nano-sheet array film was obtained, and then a smooth, continuous, uniform, dense, and PbI2-free perovskite film was formed through a reaction with CH3NH3I. After optimization, the device prepared using the in situ pre-wetted PbI2 nano-sheet array film achieved a promising PCE of 19.19%. Moreover, it also had good reproducibility and long term stability, as the devices based on the in situ pre-wetted PbI2 nano-sheet array film retained over 80% of the initial PCE after exposing to ambient air for two months.