Key Issue for the Fabrication of High-Efficiency Microcrystalline Silicon Thin-Film Solar Cells at Low Temperatures

Abstract

Hydrogenated microcrystalline silicon (µc-Si:H) p–i–n solar cells have been prepared using the plasma-enhanced chemical vapor deposition (PECVD) method at process temperatures lower than 150°C. The low-temperature deposition of µc-Si:H was found to be effective in suppressing the formation of oxygen-related donors that cause a reduction of the open circuit voltage (VOC). We demonstrate the increase in VOC by lowering the deposition temperature to less than 150°C without deteriorating other device parameters such as short circuit current (JSC) and fill factor (FF). A high efficiency of 8.9% was obtained on a textured SnO2 substrate (Asahi-U) substrate. Further improvement in the efficiency to 9.4% (VOC=0.526 V, JSC=25.3 mA/cm2, FF=0.710) was achieved by optimizing the texture of Ga-doped ZnO substrates. An attempt to increse the deposition rate is also demonstrated using 60 MHz plasma and a relatively high efficiency of 8.4% was obtained at a deposition rate of 12 Å/s.