 Currently, he is the director of the JARA-Energy, (JARA = Jülich-Aachen Research Alliance) which coordinates research at Forschungszentrum Jülich and RWTH Aachen in the field of renewable energy.Rau is well known for his various contributions to the basic principles of photovoltaic energy conversion and to improving the understanding of solar cell device physics.Most notable, perhaps, is his publication in 2007 of a paper on a "reciprocity relation between photovoltaic quantum efficiency and electroluminescent emission of solar cells".