1. Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle upon Tyne, NE1 8ST, U.K.
2. Department of Mechanical and Construction Engineering, Northumbria University, Newcastle upon Tyne, NE1 8ST, U.K.
3. Wolfson School of Mechanical, Electrical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, U.K.
4. Centre for Solar Energy Research (CSER), in the Centre for Integrative Semiconductor Materials (CISM), Faculty of Science and Engineering, Swansea University, Bay Campus, Swansea, SA1 8EN, U.K.
5. HORIBA UK Limited, Kyoto Close, Moulton Park, Northampton, NN3 6FL, U.K.