Elucidating structure-function relationships in perovskite-based materials for photovoltaic and LED application is important to push this class of materials towards implementation in commercial products. Slot-die coating is a particularly promising deposition method for high output production with minimal waste and shows the potential to print on a variety of substrates, including ultrathin flexible plastic foils. However, for a successful transition from lab-scale processes to roll-to-roll compatible methods, film formation from precursor inks has to be controlled in detail – including intermediate phases, e.g. precursor-solvent complexes, which can even be beneficial. With the perovskite absorber being the key material in a perovskite-based solar cell, structure and morphology control during thin-film formation is essential in achieving highly homogeneous and thus high-performing absorber layers. GIXS (grazing-incidence X-ray scattering) measurements are well suited to probe the influence of deposition parameters, e.g., temperature, ambient moisture and precursor composition by probing stochastically relevant large sample areas in situ. In order to better understand morphology evolution and crystallization kinetics during film formation, we investigate the conversion of slot-die coated lead iodide and slot-die coated methylammonium iodide to perovskite (MAPbI3) by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). We track the phase evolution and their respective crystal orientations over time. Using synchrotron radiation, a time resolution of around 1 s is achieved and the kinetics of the reactions become visible. Already known intermediate precursor-solvent phases can be identified by crystal structure analysis. In this work we study the influence on thin-film morphology and texture evolution during the transformation process. We see that crystalline precursor-solvent complexes can decisively influence the resulting film texture by acting as a lead iodide source that controls the level of available precursor material. We can further correlate pre-existing orientations of the lead iodide thin film to the resulting perovskite film and deduce a morphological growth model. As a reference we investigate spin-cast PbI2, MAI and MAPbI3 thin-films and look into methodical differences that can influence the film quality.

In situ GIWAXS phase and texture evolution tracking of the formation of 2-step slot-die coated MAPbI3

ACS Spring Meeting 2021

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