Optimization of the Aerosol-Assisted Solvent Treatment on Perovskite Film on Flexible Substrate Using Strain Engineering

Aerosol-Assisted Solvent Treatment (AAST) is an effective post-treatment method designed to improve the grain size of perovskite films, thereby reducing grain boundaries (GBs) and improving the performance of solar cells.^1,2 The process involves placing the perovskite film on a heated graphite block inside a cylindrical quartz reactor. A solvent aerosol of N,N-dimethylformamide (DMF), generated by a piezoelectric mister, is introduced into the reactor with the assistance of nitrogen gas. This leads to the vaporization of DMF on the surface of the perovskite film, initiating a mass transformation between grains. Smaller grains, due to their higher surface energy, are gradually dissolved, and the material is then added to larger grains, facilitating their growth. This process aligns with the Ostwald ripening model, resulting in a significant increase in grain size after just 5 minutes of AAST. Consequently, the Power Conversion Efficiency (PCE) of the device is enhanced from 18.7% to 20.0%, alongside an improvement in device stability.<br/>However, during the application of AAST on perovskite films deposited on flexible substrates, a red shift in Photoluminescence (PL) was observed. Combined with X-Ray Diffraction (XRD) analysis, this phenomenon was attributed to the in-plane compressive stress within the grain boundary of perovskite. To address this issue, the process was adapted by simply bending the perovskite film during AAST, effectively reducing the aforementioned stress. This modification maintained the balance of strain engineering, offering a nuanced approach to optimizing the treatment process for flexible substrates.