 In 1995, he moved to Bayreuth where he worked dominantly on the device physics of Cu(In,Ga)Se2 solar cells.1997, he moved back to Stuttgart to work at the University of Stuttgart, Institute of Physical Electronics, which was led by Jürgen Werner.In Stuttgart, he continued work on Si and Cu(In,Ga)Se2, but also started work on dye-sensitized solar cells, organic solar cells, and the fundamental aspects of luminescence in solar cells.