1. Department of Electrical Sustainable Energy; Delft University of Technology; P. O. Box 5053 2600GB Delft The Netherlands
2. Kavli Institute of Nanoscience Delft; Delft University of Technology; Lorentzweg 1 2628 CJ Delft The Netherlands
3. New Technologies Research Centre; University of West Bohemia; 306 14 Plzen Czech Republic