Environmental Chamber to Regulate Film Morphology for Solar Energy Materials Printing Using Additive Manufacturing and Investigating the Role of Additives in Perovskites

Thesis (Master's)--University of Washington, 2018Flexible ink solar cells are gaining increased interest from photovoltaic researchers and the rapid development in the field of additive manufacturing has made the fabrication of solution- processed hybrid organic-inorganic metal halides viable. The aim of this work is to assist the transition from lab-scale spin-coated solar cell active layer processes that cannot be effectively scaled up to a viable slot-die coat additive manufacturing process with the ultimate aim of transferring to an integrated roll-to-roll process. This thesis presents work done in solution engineering, establishing print parameters for the slot-die coater, introducing a processing step and hardware improvement to control and improve printed active layers and investigating the use of additives in perovskite precursor solutions. The perovskite precursor solution was developed based on experiments conducted on a large area flat sheet coater in ambient and a humidity-controlled room at the Washington Clean Energy Testbeds (WCET). Film deposition experiments were followed by microscopy, spectroscopy and absorbance studies on the printed films. Based on visual observation and morphology data, the print parameters and solution composition are then altered. A local atmosphere processing improvement and hardware were introduced during solution printing and the effect on the perovskite microstructure including but not limited to grain morphology, grain boundary, grain size and film roughness was analyzed. An environmental chamber incorporating an air-knife was designed, fabricated and implemented in the deposition process that makes use of a recirculation zone created by constrained nitrogen to control and improve printed films. A contour of the airflow pattern was simulated on ANSYS 18.1, giving us a visual representation and quantitative estimations of the air flow over the printed film. Through experiments, it was possible to regulate the microstructure based on the evaporation rate induced by the recirculation zone. The chamber also played a role in keeping oxygen and moisture away from the print zone, thereby offsetting issues caused by a highly hygroscopic Methylammonium Iodide (MAI). A preliminary study was done with a prototype chamber after which a large-area final chamber was built. A study on additive inclusion in perovskites was done that made use of high boiling point antisolvents to regulate crystallization dynamics. The additive concentrations were varied with respect to annealing times and printing trials were performed from these inks on the slot-die coater and compared to arrive at a desirable precursor perovskite solution composition