Liquid film coating and drying under sounding rocket microgravity conditions in systems relevant for organic solar cells

This project aims at, on the one hand, a better fundamental understanding and better control of the molecular interactions yielding the structures found in the molecular blend thin films making up the active layer of an organic solar cell, and, at the other hand, developing a new coating method, suitable for sounding rocket experiments, for solution-borne organic optoelectronics by a stationary substrate and a mobile solution.

The evaporation of the solvent causes a concentration gradient, eventually leading to an evolving phase separation. Due to the fast solvent evaporation, the phase separation process is arrested before it reaches completion.

For the blend films formed under such a process, the partial phase separation will result in a specific film structure, known as the film morphology.

In the case of an organic solar cell, the solution contains donor and acceptor molecules, and the active layer morphology is shown to be decisive for the solar cell performance. It is known that the kinetics of phase separation is slowed down under microgravity conditions.

Hence, this provides a possibility to study the early stage of the phase separation in more details, due to a more extended timescale for this process to develop.

By applying microgravity conditions in preparations, we have already found differences related to the slower phase separation.

To ensure that the whole drying process is performed under microgravity conditions, we need to prolong the microgravity timespan, which is achieved by performing the process during a sounding rocket experiment.

In this way, we can better judge the results obtained during parabolic flights and at the same time develop the wet chemistry methods for producing the thin film active layer. At the same time, we will develop this deposition method to work both under Earth and microgravity conditions.