**8. Acknowledgements**

The authors would like to express their appreciations to the technical staff of the CES Solar Cells Standards and Testing Center (CSSC) of King Mongkut's University of Technology Thonburi (KMUTT) for their assistance and valuable discussions. One of the authors, N. Patcharaprakiti receives a scholarship from Rajamangala University of Technology Lanna (RMUTL), a research grant from the Energy Policy and Planning Office (EPPO) and Office of Higher education commission, Ministry of Education, Thailand for enabling him to pursue his research of interests. He is appreciative of the scholarship and research grant supports.
