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ESR Investigation of Semiconductor Materials for Application in Silicon-based thin-film Solar Cells

Time: 10:00 AM

Date:Oct. 26th, 2012
Location: The Institute for Biomedical Engineering & Nano Science (iNANO), 67 Chifeng Road
Reporter: 肖莉红博士 (德国慕尼黑工业大学)
Comparing with the traditional c-Si solar cells, thin-fim Si solar cells offer more efficient use of the Si raw material with a reduction of the cell thickness. The technology has been developed to improve the light trapping, to reduce process temperatures for the use of low-cost substrates, to build up multi-junction ( Combining the use of thin-film a-Si:H and µc-Si:H) ) structures for better use of the solar spectrum, and to develop large-area fabrication and integration into modules. One of the key research topics of thin-film Si-based solar cells is the understanding of their electronic transport properties. Defects and impurities which have localized electronic states within the band gap are critical limiting factors. These electronic defects act as recombination centers for photo – generated charge carriers, suppress doping by acting as traps and generally lower the performance of optoelectronic devices. Therefore, the nature of defects, their formation mechanisms and their influences on the electronic transport in a-Si:H, µc-Si:H and Si alloys are of importance for thin-film Si photovoltaics. Being used as the transparent conductive window layer, hydrogenated microcrystalline silicon carbide (µc-SiC:H) has been prepared by Hot-wire chemical vapor deposition (HWCVD) method. The correlation between the paramagnetic defects, microstructure, optical and electrical properties has been discussed. Correspondingly, these properties were characterized by the spin density (NS), g-value and the lineshape of ESR spectra, Infrared crystallinity as well as optical absorption and electrical dark conductivity (σD). Samples for material research have been prepared on glass and/or Al-foil substrates with variation of the Monomethylsilane concentration (cMMS), the substrate and filament temperature (TS, TF), the gas pressure (p) and the Al-doping concentration (pTMAl/pMMS). And subsequently optimized material has been applied in single-junction solar cells, an ideal conversion efficiency of 9.6% has been achieved.

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