Photovoltaic Characteristics of iodine-doped Amorphous Carbon Thin Films Grown by Microwave Surface-Wave Plasma CVD

摘要

This paper reports the effects of iodine (I) doping on the optical, structural and photovoltaic properties of amorphous carbon (a-C) thin-films grown on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition at low temperature ( < 100°C). For film deposition, Ar and CH_4 were used as plasma source gases. The undoped and I-doped (post deposition doping) films were characterized by UV/VIS/NIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and current-voltage measurements. The optical band gap of the undoped film (3.4 eV) dropped to 0.9 eV after I-doping. The XPS results confirmed the successful doping of I in the a-C film. The Raman results indicated I-induced graphitization in the doped-film. The photovoltaic measurements show that the open-circuit voltage (V_(oc)) and short-circuit current density (J_(sc)) of I-doped a-C film deposited on n-type silicon substrate under light illumination (AM1.5, 100 mW/cm~2) were approximately 177 mV and 1.15 μA respectively and the fill factor was found to be 0.217. The use of a-C in photovoltaic solar cells is still in its infancy due to complicated microstructure of carbon bondings, high defect density, low photoconductivity and dificulties in controlling conduction type. Further research is underway to realize cheap, reasonably high efficiency and environmental friendly a-C based solar cells.