SBIR-STTR Award

This Small Business Innovation Research Phase I project will test the feasibility of using a novel Microwave/Electron Beam (EM) Gas Jet technique to prepare high stable efficiency microcrystalline silicon cells at high deposition rates. These cells, with light absorbing microcrystalline layers, have been proposed as an alternative to amorphous silicon based cells because, in contrast to the amorphous cells, the efficiencies do not degrade with long term light exposure. While microcrystalline cells with 11% stable efficiencies have been obtained, the technique used to prepare these cells requires unacceptably low deposition rates of 1-3 A/s for microcrystalline formation. The proposed technique is unique in that it utilizes a microwave source, an electron beam and a Gas Jet that produces near supersonic gas speeds. The microwaves efficiently decompose the silane gas to create high deposition rates and with large amounts of hydrogen dilution generate large atomic hydrogen fluxes that are important for microcrystalline formation. The electron beam is required to stabilize the plasma while high gas speeds created by the Gas Jet minimize any detrimental gas phase interactions. The proposer will demonstrate in this program that high quality microcrystalline silicon materials and solar cells can be prepared at high rates with this novel deposition technique. The success of this program will ultimately lead to a wider use of Photovoltaic (PV) products thereby reducing the dependency on fossil fuel energy sources. Development of a high deposition rate technique to prepare high quality microcrystalline silicon could also be applied in other industries such as thin film transistors, photodetectors, and photosensors.

This Small Business Innovation Research (SBIR) Phase II will further develop a novel microwave Gas Jet technique for its use the production of high efficiency microciystalline silicon solar cells at high deposition rates. In Phase I, it was demonstrated technique can he used to prepare microcrystalline silicon i-layers for single-junction nip solar cells at deposition A/s, rate 3-5 times high than those obtained using standard techniques. These rates make the large-scale production microcrystalline cells economically feasible. Microcrystalline cells are an attractive alternative to amorphous silicon germanium cells as red light absorbing structures in high efficiency amorphous silicon based multi-junction solar cell devices because their efficiencies do not degrade with long-term light exposure. Thus use of the microcyrstalline materials will lead to higher stable efficiencies for the multi-junction cells. In Phase II, the solar cell efficiencies for these microcrystalline cells will be further improved through optimization of the deposition conditions which include the use of carbon and fluorine based gases, and use of new load-locked hardware for the preparation of doped layers without air exposure of layer interfaces. Also, hardware designs for large-scale usage of the Gas Jet technique will be tested. A successful program will lead to the replacement of the standard rf glow discharge deposition technique in ECD's joint venture solar module production lines with the Gas Jet technique as well as the replacement or red-light absorbing amorphous silicongermanium layers in ECD's triple-junction solar cell design with more stable microcrystalline layers. As a result, we will fabricate modules with higher stable efficiencies at reduced costs. This will lead to a wider use of Photovoltaic (PV) products thereby reducing the dependency on fossil fuel energy sources. Development of a high deposition rate technique to prepare high quality microcrystallitic silicon could also be used in other applications such as in thin film transistors, photodetectors, and photosensors.