Improvement of amorphous silicon solar cell performance by inserting a tungsten oxide layer between zinc oxide and p-type amorphous silicon carbide

Amorphous silicon (a-Si:H) solar cell fabricated on zinc oxide (ZnO) has poor fill factor (FF) resulting from a high resistive contact between ZnO and p-type amorphous silicon carbide (p-a-SiC:H) films. This is due to the existence of a wide depletion region in the p-a-SiC:H adjacent to the ZnO/p-a-SiC:H interface. To overcome this contact problem, an amorphous tungsten oxide (WO₃) layer was inserted between ZnO and p-a-SiC:H. It was found that the insertion of the WO₃ layer improves the cell performance by reducing series resistance. Since this layer has higher optical band-gap (3.35 eV) than a-SiC:H (2.1 eV), there was no change of current density in short wavelength regions. A radio-frequency magnetron sputtering apparatus was used to deposit ZnO:Al on glass. The structure of the cells was ZnO:Al (800 nm)/n-a-WO₃ (4 nm)/p-a-SiC:H (10 nm)/i-a-Si:H (270 nm)/n-a-Si:H (30 nm)/Al (100 nm). As a result of the WO₃ insertion, the efficiency of the solar cell enhanced from 6.89% to 7.45%.