The solution-manufacturability of the light harvesting layer is a key common denominator in organic, inorganic and hybrid emerging thin film photovoltaics and as such requires understanding and mastering the solution-to-solid phase transformation process leading to the formation of the light harvesting material during solution processing. This talk will present our most recent understanding of the solution-to-solid phase transformation during solution-processing (e.g., spin coating and blade-coating) in conditions which lead to highly efficient solar cells in our laboratory. In the first part, we will focus on the influence of additives on the formation of the organic bulk heterojunction layer in the context of polymer:fullerene and oligomer:fullerene systems. In the second part, we will discuss our findings with respect to perovskite thin film formation kinetics and mechanisms for different halides (chlorine, bromine and iodine), solution compositions, and substrate surfaces.
The unprecedented insight into the formation of organic and perovskite light absorbers was made possible by combining multiple characterization probes in situ during solution processing to monitor the solution thinning/evaporation and solution concentration (via time-resolved optical reflection/ellipsometry), as well as the pre-aggregation of the solute and the nucleation and growth of the solid state components (via time-resolved UV-visible transmission/absorption and grazing incidence x-ray scattering).