SBIR Phase II: Fabrication of Low-bandgap Nano-crystalline SiGeC Thin Films Using the Plasma Enhanced Chemical Vapor Deposition (PECVD) Technique

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This SBIR Phase II project is to develop thin film tandem solar cells, comprising of nanocrystalline silicon and silicon carbon (nc-Si and nc-Si:C) absorber materials, with a conversion efficiency of ~20%. The phase I project successfully developed one of the key components, i.e. intrinsic nc-Si:C with a band gap, Eg, of ~ 1.5 eV and with good opto-electronic properties. This key material will be used initially in phase II to fabricate cells in a single junction configuration with an efficiency goal of ~10%. Previously, developed "device quality" nc-Si materials, with Eg ~1.1eV, were used to produce solar cells with efficiency ~8%. Integrating the two devices in a tandem junction configuration is forecast to yield efficiencies of ~18%. Further improvement in the tandem junction device efficiency,to ~20%, may be achieved via the use of buffer layers at the p/i or i/n interfaces and by increasing the grain size which would boost the open circuit voltage, Voc.Higher efficiency thin film tandem solar cells will be critical to achieving the low costs necessary to achieve widespread adoption of photovoltaic energy generating systems.