1. Australian Centre for Advanced Photovoltaics, School of Photovoltaic and Renewable Energy Engineering, University of New South Wales (UNSW), Sydney 2052, Australia
2. Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, U.K.
3. Dimond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, Oxfordshire, U.K.
4. Advanced Technology Institute, Department of Electrical and Electronic Engineering, University of Surrey, Guildford GU2 7XH, Surrey, U.K.