1. Institute of Photonics and Nanotechnology, Faculty of Physics, Vilnius University, Saulėtekio al. 3, LT 10257 Vilnius,
Lithuania
2. National Renewable Energy Laboratory, 15013
Denver West Parkway, Golden, Colorado 80401, USA
3. Center for Materials Research, Washington State University, Pullman, Washington 99164, USA
4. Faculty of Physics, Vilnius University,
Saulėtekio al. 3, LT 10257 Vilnius, Lithuania