An HZB team at BESSY II recently analyzed the crystallization processes within optimized inks used for the production of metal-halide perovskite thin-films for photovoltaic modules . A model has also been developed to assess the kinetics of the crystallization processes for different solvent mixtures. The results could be of high importance for the further development of perovskite inks for industrial-scale deposition processes of these semiconductors.
For the production of larger area photovoltaic modules, the team of Dr. Eva Unger develops printing and coating processes in which the perovskite semiconductor is processed from inks containing the precursors dissolved in solvents. The composition of the ink determines the material formation mechanism with the solvent affecting the process by its rheological properties, evaporation rate and participation in intermediate phases. "Our research question in this project was: How can we rationalize the difference in crystallization kinetics when using different solvents," explains Unger, who heads the Young Investigator Group Hybrid Materials Formation and Scaling.
In solvents with only one component, the crystallization process is determined by the evaporation rate. "In mixtures of solvents, evaporation is dominated by the most volatile component that evaporates the fastest. This changes the ratio of solvents that are present upon crystallization", says Dr. Oleksandra Shargaieva, postdoc in Unger's team.
At the KMC-2 beamline of BESSY II, she was able to analyze the formation of the perovskite semiconductor and crystalline intermediate phases incorporating solvent molecules during the evaporation of the solvents. “I found that the formation mechanism critically depends both on the solvents evaporation rate and binding strength to the lead-halide. “These insights will help to predict the kinetics of crystallization processes of the perovskite thin film for different solvent combinations based on the properties of the precursor solutions”, says Shargaieva.
"There is still a lack of systematic knowledge when scaling up from laboratory scale to industrial area sizes. With these results we pave the way for further ink design to enable industrial-scale manufacturing of perovskite thin films of high quality”, says Unger.