1. Department of Physics, Nazarbayev University, Astana KZ-01000, Kazakhstan
2. First Solar, Inc., Perrysburg, Ohio 43551, USA
3. School of Electrical and Computer Engineering, National Technical University of Athens, Athens GR-15780, Greece
4. First Solar, Inc., Perrysburg, Ohio 43551, USA and Department of Physics, Nazarbayev University, Astana KZ-01000, Kazakhstan