1. Photovoltaics Laboratory Korea Institute of Energy Research Daejeon 34129 Republic of Korea
2. Department of Materials Science and Engineering Korea University Seoul 02841 Republic of Korea
3. Amtech Systems Inc. Tempe AZ 85281 USA
4. School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta GA 30332 USA
5. KU‐KIST Green School, Graduate School of Energy and Environment Korea University Seoul 02841 Republic of Korea