Improved Control of Perovskite Thin Film Fabrication via Optical In Situ Spectroscopy and Reactive Spin Coating

Efficient solar cells require a high-quality halide perovskite (HP) film, which is typically achieved through a solution-based solvent engineering spin coating approach. Here, HP crystallization is induced by applying an antisolvent (AS) to the precursor solution film on the spinning substrate after a specific spinning time. The process involves various controllable and uncontrollable parameters that need to be considered. As a result, fabrication recipes (such as spin speed or timing of AS dispensing) are usually developed empirically and vary between labs. Additionally, factors like changes in the atmosphere that are hard to control can introduce substantial variations between and even within batches of devices.<br/><br/>In this work we developed a closed-loop feedback system based on our multimodal optical In-Situ spin coater system in combination with a real-time analysis of the optical spectra during spin coating. We optically monitor the solvent layer thickness as the parameter of interest during the spin coating process. When the target level is reached, the HP crystallization is autonomously induced by dispensing the AS via a syringe pump. This method compensates for the effects of uncontrolled parameters, like variation in solvent evaporation rate due to atmospheric changes, thus leading to reproducible film quality for different perovskite compositions.[1]<br/><br/>Thus, the reactive spin coating approach will open up future possibilities to simplify the transfer of recipes from one laboratory to the next by removing the influence of external effects, such as atmosphere or the human factor, on the layer formation as the processing is only based on system-internal parameters. Additionally, the reactive approach is not limited to the solvent layer thickness as the parameter of interest. Any optically accessible property of the solvent film, such as precursor state composition, can be a potential parameter for the reactive approach. Eventually, our approach also represents a valuable contribution for an in general improved process control in the solution processing of halide perovskite thin films, making it relevant for their successful upscaling and commercialization in optoelectronic devices in the future.<br/><br/>[1] Biberger et al. J. Mater. Chem. C, 2024, <b>12</b>, 6415-6422