Tailored upscaling of solution-based thin film fabrication of halide perovskites enabled by multimodal optical in-situ spectroscopy (HOLD-MOISS)

• Applicant: Professorin Dr. Anna Köhler, since 11/2022
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510654404

Since the first reports of metal-halogen perovskites used as absorber material in perovskite solar cells (PSCs), the corresponding efficiency of these devices has increased rapidly to 25.5 %. Most of the high-efficiency PSCs were and still are produced on a laboratory scale on a millimetre scale, solution-based by means of spin coating. However, to realise perovskite thin films and hence solar cells on a larger scale, methods such as blade coating are relevant. The efficiency of PSCs produced by such methods is currently still clearly lower than the corresponding cells produced by spin coating. This efficiency gap is due to differences in the final layer properties, which in turn are due to method-dependent differences in the perovskite film formation process. The key to building a holistic understanding of the film formation processes of halide perovskites, which currently does not exist but is urgently needed, is to identify and understand mechanistic differences in the crystallisation behaviour between spin coating and scalable methods such as blade coating. Accordingly, the development of such a method-independent understanding is the goal of this project. To this end, we will elucidate the specific influence of the properties of the precursor solutions and surfactants on the crystallisation processes occurring during the solution-based one-step film manufacturing of the model perovskite methylammonium lead triiodide. In particular, we address the roles of iodoplumbate complexes in the reactant solutions, solubility of the employed solvent, its evaporation rate and addition of surfactants, in the formation of the perovskite during film formation. To this end, we investigate the film formation processes in depth using multimodal optical in-situ spectroscopy and correlate the resulting findings with the results of detailed investigations of the structural, morphological and optoelectronic properties of the final thin films. These investigations will be complemented by the evaluation of the functionality of the fabricated films in solar cell configuration. With that we will finally be able to formulate method-independent strategies for solution-based one-step coating of to achieve perovskite thin films with tailored optoelectronic properties. This will enable a successful transfer from small-scale spin coating to large-scale roll-to-roll compatible methods, such as blade or slot die coating, and thus will contribute to advancing the commercialisation of perovskite solar cells.

• DFG Programme: Research Grants
• Co-Investigator: Professorin Dr. Eva M. Herzig
• Ehemaliger Antragsteller: Dr. Fabian Panzer, until 11/2022