[1] Helmholtz Zentrum Berlin Mat & Energie GmbH, Div Solar Energy, D-12489 Berlin, Germany
[2] Univ Oxford, Clarendon Lab, Oxford OX1 3PU, England
[3] Univ Potsdam, Inst Phys & Astron, D-14476 Potsdam Golm, Germany
[4] Univ Jaffna, Dept Phys, Jaffna 40000, JA, Sri Lanka
[5] Tech Univ Berlin, Fac Elect Engn & Comp Sci, D-10587 Berlin, Germany