3 October 2017
Solar-Tectic granted US patent for low-cost, high-efficiency III-V thin-film tandem solar cell on glass substrate
Solar-Tectic LLC of Briarcliff Manor, NY, USA says that the US Patent and Trademark Office has granted it US patent 15/205,316 ‘Method of Growing III-V Semiconductor Films for Tandem Solar Cells’ for high-efficiency and cost-effective solar cells made on glass or flexible plastic substrates for various industrial applications, such as rooftops to help charge battery-powered electric automobiles (EVs). The technology also promises to be useful in manufacturing light-emitting diode (LED). The inventor is CEO Ashok Chaudhari.
The patent (the first ever for a thin III-V layer on crystalline silicon thin-film) covers group III-V compounds such as gallium arsenide (GaAs) and indium gallium phosphide (InGaP) for the top layer, as well as all inorganic materials, including (silicon, germanium etc) for the bottom layer. In the patented technology, ultra-thin films of III-V materials and silicon (or germanium) replace expensive, thicker wafers, lowering costs dramatically.
III-V tandem (or multi-junction) cells fabricated on wafers such as silicon are being developed with high efficiencies of about ~30%. The highest dual-junction cell efficiency (32.8%) came from a tandem cell that stacked a layer of GaAs atop crystalline silicon. Manufacturing costs are expensive, especially if a germanium wafer is used as the bottom material in the two-layer tandem structure. To compete with low-cost silicon wafer technology (which comprises 90% of the global solar panel market), efficiencies must not only be as high as silicon wafers or greater (lab records of 21.7% and 26.7% for poly- and monocrystalline silicon-based cells, respectively) but manufacturing costs must also be lower.
Solar-Tectic says that this is achievable in the patented technology, which uses common industrial manufacturing processes and at low temperature. There is no wafer involved, which saves material and energy. Instead, a thin film allows precise control of growth parameters. A glass substrate instead of a wafer also allows for a bifacial cell design for increased efficiency.
A cost-effective ~30%-efficient III-V tandem solar cell in today's market could dramatically reduce the balance of system (BoS) costs and reduce the need for fossil-fuel-generated electricity, says the firm. Silicon wafer technology based on polycrystalline or monocrystalline silicon could become obsolete, it adds.
Importantly, the entire patented process for the III-V tandem cell can be environmentally friendly, since non-toxic metals can be used to deposit the crystalline thin-film materials for both the bottom layer in the tandem configuration as well as in the top III-V layer, notes Solar-Tectic.
The firm adds that the technology also has great promise for LED manufacturing using, for example, gallium nitride.
Solar-Tectic has launched a Tandem Series of solar cell technologies, which includes a variety of different proven semiconductor photovoltaic materials for the top layer on silicon and/or germanium bottom layers. Recently, patents were also granted for a tin perovskite and germanium perovskite thin-film tandem solar cell.
The US International Trade Commission (ITC) ruling on 22 September means that it is likely that tariffs will be imposed on crystalline silicon wafers sold in the USA. However, these tariffs will not apply to thin-film solar cell technology such as Solar-Tectic’s, the firm notes.