Characterization of ZnO:Ga transparent contact electrodes for microcrystalline silicon thin film solar cells

Gallium-doped zinc oxide (ZnO:Ga) thin films are of interest to the semiconductor industry as transparent conductive surfaces and as transparent contact electrode layers for applications such as microcrystalline silicon (μc-Si) thin film solar cells. Physical vapor deposition (PVD) via sputtering is commonly used to produce thin films such as ZnO:Ga, but film quality and characteristics depend significantly on the PVD processing parameters. For use as contact electrode layers in μc-Si thin film solar cells, this study investigates some of the important changes of ZnO:Ga thin films that result from varying DC magnetron PVD sputtering parameters, specifically the working power (500, 1200, and 1900 w), process gas (Ar, Ar/O2=50/0.2 sccm) and working pressure (0.74 and 1.06 Pa). Process temperature is held at 200 °C because thin film solar cells are damaged above 200 °C. Adding O2 to the Ar carrier gas improved transmittance but the resistivity suffered. However, high-sputtering power solved the resistivity problem. Additionally, the effects of the produced ZnO:Ga material when applied as multi-layer front and back layer electrodes to μc-Si thin film solar cells is evaluated in terms of open-circuit voltage (ΔVOC), short-circuit current density (ΔJSC), fill factor (ΔFF) and efficiency (Δη) of the cells.