Boundary layer tuning induced fast and high performance perovskite film precipitation by facile one-step solution engineering

As promising highly-efficient and low-cost photovoltaic devices, perovskite solar cells must be made of compact and pin-hole free perovskite films. One-step solution engineering is a most efficient and low-cost precipitation of high quality perovskite films. However, the difficulty in controlling the precipitation and pin-hole formation in perovskite films makes this one-step solution engineering a great challenge. Here, we report, for the first time, a fast and high performance perovskite film precipitation by tuning the boundary layer during the solution processing of the perovskite film. Theoretical analyses and simulations were carried out alongside the experiments, and the results consistently showed that a high velocity and low temperature of the air flow could effectively reduce the thickness of the boundary layer. Subsequently, evaporated solvent molecules would diffuse through the boundary layer more easily, and then solvent evaporation becomes quicker, resulting in a high quality and pin-hole free perovskite film. As a result, the highest efficiency of 17.87% was achieved for planar perovskite solar cells (with an active area of 0.1 cm²) with the perovskite film precipitated under these air conditions. Furthermore, the efficiency reached as high as 12.72% with a 1.08 V open-circuit voltage for a 1 cm² planar perovskite device. This essentially opens the door to developing high quality perovskite film precipitation approaches by tuning the boundary layer during facile one-step solution engineering.