Applications of ZnO in Cu(In,Ga)Se₂ solar cells

The influence of preparation conditions of the transparent conductive oxide (TCO) ZnO in a magnetron sputtering process on the properties of solar cells based on Cu(In,Ga)Se₂ absorbers is examined. Criteria for optimized ZnO layers for high efficiency applications are given. Preparing at substrate temperatures below 200°C, the sputtering conditions have only a minor effect on the device properties. A novel high rate reactive DC-sputtering process has been developed leading to highly transmissive conductive ZnO layers with no additional substrate heating. TCO layers suitable for module applications have been deposited in less than 5 minutes. Solar cell device properties using ZnO prepared with this process are comparable to cells with standard RF-sputtered ZnO. This demonstrates the possibility to apply a scalable high deposition rate ZnO process to high efficient Cu(In,Ga)Se₂ solar cells. A significant cost reduction for large area applications is expected with this novel process