1. University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom
2. Department
of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
3. Department
of Chemistry and Geochemistry, Colorado School of Mines, 156 Coolbaugh Hall, 1012 14th Street, Golden, Colorado 80401, United States
4. Oxford Photovoltaics Ltd, Centre for Innovation
and Enterprise, Begbroke Science Park, Woodstock Road, Oxford, OX5 1PF, United Kingdom