Development of transparent-conducting oxide (TCO) back contact for Cu(In,Ga)Se 2 (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.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films