René Janssen leads the interdepartmental research group Molecular Materials and Nanosystems at Eindhoven University of Technology, which is part of the departments Chemical Engineering and Chemistry as well as Applied Physics. The research objective of the group is to investigate and develop molecules, macromolecules and (nano)structured materials with tailored physical properties. The interest in these functional molecular materials and nanosystems is driven by the scientific challenge to understand the underlying mechanisms of the physical phenomena in systems of reduced dimensionality, down to the molecular level. Future applications are in organic and polymer solar cells, electrochemical cells, transistors and diodes.

Janssen has in particular obtained a thorough understanding of the subtle interactions of light and the chemical and electrical structures at the nanoscale. This has led to major improvements in the efficiency of polymer solar cells. The group now works on multi-junction molecular solar-to-electricity conversion devices, to further improve efficiencies. Another focus in Janssen's research is solar-to-fuel conversion using organic semiconductors in a process mimicking natural photosynthesis. To this aim new organic materials and electrocatalysts are being developed.