11-Jan-2023: Talk by Dr. Konstantin Schötz
Investigating perovskite film formation using in situ optical spectroscopy
A necessary part of efficient solar cells are high quality absorber layers. For solution-processable semiconductors, such as organic semiconductors or metal halide perovskites, the quality of this absorber layer is largely determined by the crystallization processes during film formation. Apart from adjusting process parameters, the final film quality can also be optimized by additives such as passivating agents. Instead of only evaluating the impact on final film properties, recently more focus is set on understanding the film formation process itself, which can be investigated by, e.g., in situ optical spectroscopy.
This talk gives a brief introduction to in situ optical spectroscopy and discusses how it can be used to understand the film formation of different material systems and processing methods. With these insights, the influence of the ionic liquid BMIMBF4 on the film formation of the model perovskite methylammonium lead iodide (MAPbI3) upon one-step spin coating and the solvent engineering approach is investigated. While the formation of solvent complex phases appears to be unaffected by the presence of the ionic liquid, the following perovskite crystallization is delayed for the one-step processing and slowed down for both processing approaches. A similar decrease of the perovskite growth rate is observed for later dripping times of the anti-solvent. This decrease is associated with a change of the evolution of the PbIx(x-2)- species, which in turn is affected by the presence of the ionic liquid. Still, in the as-coated films the IL efficiently passivates defect states. Finally, future prospects of in-situ optical spectroscopy are discussed.