Strategies to obtain stoichiometric perovskite by sequential vapor deposition learned by modeling the diffusion-dominated formation of perovskite films

Compared to solution approaches, vapor–solid reaction (VSR) processes have advantages in fabricating multistack perovskite solar cells (PSCs). Here, we modeled the formation of perovskite by VSR through combined experimental and simulation analyses. Scanning electron microscopy and X-ray diffraction characterizations at the turning points of the experimentally observed W-shaped in situ electrical resistance curves suggest a diffusion-dominated growth mechanism. Simulation reveals that to obtain stoichiometric perovskite films, we need to accelerate the diffusion of methylammonium iodide (MAI) in PbI2 and slowly supply MAI vapor. Experiments were conducted to verify the diffusion-dominated formation model. This work sheds important light on rational design of new VSR approaches to fabricate more effective PSCs.