Secondary crystal growth for efficient planar perovskite solar cells in ambient atmosphere

Significant progress has been made in perovskite solar cells by various effective film-forming methods. Solution-process methods for the perovskite film appropriate under ambient conditions are desired to be explored for the practical industrialization. Here, a secondary crystal growth strategy is developed for the fabrication of perovskite film in ambient atmosphere. By this method, the conversion from PbI2 to CH3NH3PbI3 on the planar substrate can be completed, overcoming the limitation of standard sequential deposition. After secondary growth, high-quality crystals are obtained and compact densely to form a pinhole-free film. Exceeding 17% of power conversion efficiency is achieved for planar CH3NH3PbI3 devices by controlling the reaction time of two stages carefully. This method can be easily controlled, reproduced and performed in the ambient, which meets the industrial requirements for highly efficient, low cost planar perovskite solar cells.