Uni-Solar tweaks tech roadmap with back reflector, deposition upgrades

PV World gets the skinny (and an analyst’s take) on ECD/Uni-Solar’s plan to boost conversion efficiency for laminates, cells, and modules thanks to improvements in light-trapping, high-rate deposition, and a hybrid absorber material.

by Debra Vogler, senior technical editor, and James Montgomery, news editor Photovoltaics World

June 10, 2010 – Banking on improvements in light-trapping, high-rate deposition, and a HybridNano technology, Uni-Solar expects to be able to reach a conversion efficiency of 12% by CY2012 with the potential to go to 20+% for its product line. Currently, the company’s laminate efficiency is at 8.2%; by late spring 2011, the company expects to be at 10%.

With respect to light-trapping, Subhendu Guha, SVP of Energy Conversion Devices and chairman of its subsidiary United Solar Ovonic, noted that currently there is still a great deal of red and IR light that remains unabsorbed. The company uses a back reflector in its multi-junction solar cell to reflect and scatter light so it has multiple passes through the cell to increase absorption. It has now developed a proprietary back reflector (see cross-section below) that is not only a good reflector, but also an excellent scatterer, according to Guha. The company reports that the new back reflector has increased the current density by about 10%.

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A proprietary deposition process has also been developed — one that has demonstrated uniformity over a large area, and increases the cell (aperture) efficiency from its current value of 8.2% (6.7% module efficiency) to 10% aperture (~9.4% module), while able to achieve a deposition rate that is almost twice as fast as the previous method. Without presenting details in its news conference materials, the company highlighted its cathode design as being a key factor. The company has started retrofitting its deposition systems with the new process and expects that laminates with an efficiency of 10% will begin coming out of its Auburn Hills (Michigan) plant in CY2010.

In a research report, Deutsche Bank analyst Steve O’Rourke notes that raising present laminate efficiency of ~6.7%/8.2% aperture efficiency to ~9.4%/10% reflects a ~40% increase in laminate conversion efficiency, which should result in lower material costs and higher rooftop power density. He calculates that the jump from 8.2% to 10% reflects a ~22% relative increase in conversion efficiency/peak power output, which by itself would increase a 30MWp line rated throughput to ~37MWp. Combined, the improved back reflector and faster deposition process would double the company’s per-line throughput to 60MW, he says, adding that the proposed upgrade to 12% efficient cells would lower production costs to $0.95/Wp.

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The third rail of the company’s roadmap is its HybridNano technology that replaces the SiGe alloy in the green and red light-absorbing layers (middle and bottom cells) in the multi-junction solar cell. The material absorbs red and IR wavelengths more efficiently and is free of light-induced degradation. The new technology has already demonstrated a large-area efficiency of ~11% and will be incorporated into production lines in 2011, after the company improves large-area uniformity. The company expects to provide cells with a targeted efficiency of about 12% by CY2012.

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Financially speaking, improving the conversion efficiency and deposition rate (i.e., throughput) will help reduce cost/W and capex/W, the company says. O’Rourke suggests it will cost about $15M-$20M worth of line upgrades, and doubling throughput to 60MW would end up costing about $0.50-$0.60/Wp in capex. “With only a moderate increase in consumables, we estimate manufacturing cost could be cut by upwards of 30%, pushing present full utilization production cost of ~$1.50/Wp closer to <$1.10/Wp by mid next year,” he claims.