Microgravity effects on solution chemistry and partial phase separation is a path for better understanding of the blend film morphology

This application concerns a new project, aiming at a better fundamental understanding and, hence, better control of the molecular interactions resulting in the morphologies found in the molecular blend thin films making up the active layer of an organic solar cell.

The morphology stems from the partial phase separation that occurs when the solvent evaporates from the solution of donor and acceptor (and sometimes additional) molecules, so leading to a fast-developing concentration gradient.

By applying microgravity conditions to the process of preparing the active layer blend solid film from a solution coating of a substrate, it will be possible to better characterise the molecular interactions during the process. Further, it is known that the kinetics of phase separation is slowed down under microgravity conditions.

Hence, under microgravity, the timescale for the phase-separation process is extended and the initial part of the phase-separation can be studied in more detail.

The characterisation of the blend films’ morphology and its influence on the photophysical charge transfer processes will mainly be performed through atomic force microscopy combined with infrared spectroscopy and time-resolved fluorescence spectroscopy, respectively. Microgravity conditions can be reached on parabolic flights and with sounding rockets.

Both methods are included in the project.Combining the new observations with fluid mechanics calculations, thermodynamics, and theoretical modelling of the system´s solution chemistry will yield an opportunity to find less environmentally and health-damaging solvents than those frequently used in research laboratories.

To find these less harmful solvents, a model based on solution thermodynamics, yielding the possibility to match the properties of the solvent with the solutes, will be employed.

Finding more environmentally and health-friendly solvents is a necessity in order to be able to manufacture cheap and flexible solar cells on an industrial scale in the future.The applied project is part of a multi-disciplinary research programme at Karlstad University, in which scientists from different fields, e.g., chemistry, materials physics, and modelling, develop projects in the field of molecular interactions under normal and microgravity conditions.

This research is conducted in national as well as international collaboration.