A repeated interdiffusion method for efficient planar formamidinium perovskite solar cells

A repeated interdiffusion method is described for phase-stable and high-quality(FA,MA)PbI_3 film. The crystallization and growth of the perovskite films can be well controlled by adjusting the reactant concentrations.With this method, dense, smooth perovskite films with large crystals have been obtained. Finally, a PCE of 16.5% as well as a steady-state efficiency of 16.3% is achieved in the planar perovskite solar cell.