Control of Structural and Electrical Properties of Indium Tin Oxide (ITO)/Cu(In,Ga)Se2 Interface for Transparent Back-Contact Applications

• Published in: Journal of physical chemistry. C 2019-01, Vol.123 (3), p.1635-1644
• Main Authors: Son, Yu-Seung, Yu, Hyeonggeun, Park, Jong-Keuk, Kim, Won Mok, Ahn, Seung-Yeop, Choi, Wonjun, Kim, Donghwan, Jeong, Jeung-hyun
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b11149

Development of transparent-conducting oxide (TCO) back contact for Cu­(In,Ga)­Se2 (CIGS) absorber is crucial for bifacial CIGS photovoltaics. However, inherent GaO x formation at the TCO/CIGS interface has hampered the photocarrier extraction. Here, by controlling the Na doping scheme, we show that the hole transporting properties at the indium–tin oxide (ITO)/CIGS back contact can be substantially improved, regardless of the GaO x formation. Na incorporation from the glass substrate during the GaO x forming phase created defective states at the interface, which allowed efficient hole extraction from CIGS, while post Na treatment after GaO x formation did not play such a role. Furthermore, we discovered that an almost GaO x -free interface could be made by reducing the underlying ITO film thickness, which revealed that ITO/CIGS junction is inherently Schottky. In the GaO x -free condition, post-Na treatment could eliminate the Schottky barrier and create ohmic junction due to generation of conducting paths at the interface, which is supported by our photoluminescence analysis.