Influence of ion bombardment on microcrystalline silicon material quality and solar cell performances

Microcrystalline hydrogenated silicon growth with VHF-PECVD was examined in an industrial type parallel plate KAI™ reactor. The influence of pressure on material quality was studied in single junction solar cells. Solar cells with their intrinsic layer prepared at higher pressures exhibit remarkable improvements, reaching 8.2% efficiency at 3.5 mbar. Further analyzes showed that μc-Si:H intrinsic layers grown at higher pressures have a significantly lower defect density. These results are attributed to lower ion bombardment energies due to higher working pressures, which improve the microcrystalline material quality. Layer amorphization with increasing power density is observed at low pressure. Calculations show that the average ion energy drops from roughly 20 eV to a few eV in the pressure range studied.