1. Department of Physics, Faculty of Sciences, Mugla Sitki Kocman University, Kotekli Yerleskesi, Mugla TR-48000, Turkey.
2. Forschungszentrum Jülich, IEK-5 Photovoltaik, 52425 Jülich, Germany.
3. Institut für Physik, Carl von Ossietzky Universität Oldenburg, 26111 Oldenburg, Germany.