1. Solar Energy Materials and Systems (SEMS) Institut de Recerca en Energia de Catalunya (IREC) Jardins de les Dones de Negre Sant Adrià de Besòs 08930 Barcelona Spain
2. Electronic Engineering Department Polytechnic University of Catalonia (UPC) c/Jordi Girona 1 08034 Barcelona Spain
3. Faculty of Technology, Design and Environment Oxford Brookes University Headington Campus Oxford OX3 0BP UK