Importance of PbI2 morphology in two-step deposition of CH3NH3PbI3 for high-performance perovskite solar cells*

Controlling the morphology of the perovskite film is an effective way to improve the photoelectric conversion efficiency of solar cell devices. In this work, we study the influence of the crystallization condition on PbI2 morphology and the performances of resulting perovskite solar cells. The PbI2 morphologies and coverage rates under different formation conditions such as solvent effect, slow crystallization at room temperature and substrate-preheating, are found to be of crucial importance for preparing high-quality perovskite. The generation of loosely packed disk-like PbI2 film with interpenetrating nanopores promotes the penetration of methyl ammonium iodide (MAI), leading to a better crystallinity of the perovskite film, and a best repeatable power conversion efficiency of 11.59% is achieved when methyl ammonium lead triiodide (CH3NH3PbI3, MAPbI3) is employed. In addition, an excellent device is also obtained with an efficiency of more than 93% to remain after working for 43 days.