Effect of low-temperature annealing of supercritical carbon dioxide on perovskite thin film crystals

The crystal quality of the perovskite thin film directly influences the conversion efficiency of the cell, serving as the absorption layer of perovskite solar cells. Different annealing methods can present remarkable impacts on the quality of perovskite films. Conventional low-temperature thermal annealing makes it difficult to quickly and thoroughly remove the residual solvent inside the film. In this study, the supercritical carbon dioxide (ScCO2) annealing method was demonstrated to achieve low-temperature annealing upon perovskite thin film. ScCO2 can penetrate the inside of the film to accelerate the diffusion of residual solvent molecules. The surface morphology, crystallinity, crystal deformation, and internal solvent residue of six films prepared by different methods were studied, focusing on the effects of solvent diffusion rate on crystal quality in ScCO2 and conventional annealing. The results show that ScCO2 can enhance the solvent diffusion ability at low temperatures. The thin film crystals formed by ScCO2 annealing have less deformation than conventional high-temperature annealing, which can reduce the interface defects caused by conventional low-temperature annealing and avoid solvent residue.