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EETE SEP 2015

Energy Harvesting Natcore takes silver out of photovoltaics By Julien Happich Research company Natcore Technology claims its scientists have produced a low-cost all-back-contact silicon heterojunction photovoltaic structure in which silver has been completely eliminated, being replaced by aluminium. The findings at the firm’s Rochester R&D Center are key to lower the cost of mass-produced silicon photovoltaic cells and could be licensed to large producers looking at cutting over 10% off their raw materials costs. Traditionally, and so for the last 60 years, silver has been the conductor of choice to manufacture the electrodes in solar cells, for its high-conductivity metal despite its high price. Indeed, with the average solar panel using about 14 grams of silver, the metal can represent over 48% of the metallization cost of a solar cell, or about 11% of the total raw material cost of a solar module. At today’s prices, silver costs about $0.491 per gram. The same quantity of aluminum costs $0.0016, about 0.3% of the cost of silver. The cost saving realized by switching from silver to aluminum are important, even considering that it would be necessary to use twice as much aluminum as silver in order to have an equal amount of conductivity from cell to cell. The raw material cost of aluminum would still be just 0.6% of the direct material cost of using silver in the cell. Although Dr. David Levy, Director of Research & Technology at Natcore’s Rochester (NY) R&D Center didn’t want to share more details about the exact pattern geometries and processes yielding a full silver replacement at no conductivity loss, he expects that in the case of black silicon and aluminium, the company will get revenues not only from licenses and royalties but also from materials sales. Patents are pending for proprietary laser technology to apply the back contacts to the rear of the cell as well as for other critical aspects of the low-temperature process. “Licensing our aluminum patterning process is one of our goals. Three companies (two in the U.S., one in Australia) have expressed interest. These are all companies that are planning to get into solar energy. They want to build cell fabs, module fabs, and/or power plants”, Levy wrote EETimes Europe in an email. So what have been the challenges to use aluminium instead of silver so far? “Part of the historical challenge has been the avoidance of a corrosive ‘galvanic couple’ and fatigue life of aluminum. The Natcore solution has overcome these hurdles. Three other main issues impede the use of aluminum in the types of cells that we are demonstrating. Its lower conductivity than silver means that thicker layers are required, which can pose problems for certain manufacturing techniques. Aluminum layers can also be prone to oxidation and thus poor electrical properties. Finally, it is difficult to apply aluminum at atmospheric conditions with near bulk conductivity, especially with methods that do not require high temperature and inert atmosphere sintering. High temperature steps would be incompatible with many of the devices we are demonstrating. Our technology addresses these issues. While we cannot go into details of the structure due to its proprietary nature, expect details to emerge in the next few months as we produce advanced demonstrations and secure the necessary patent protection”. Today, roughly 47 metric tonnes of silver are currently required to generate 1 GW of solar power. That demand translated into roughly 1900 metric tonnes of silver in 2014, or about 6% of the total demand for the metal. Before Natcore’s achievement, that demand was projected to rise to 15% of the total market in 2018, but the company is hoping it will have an impact on this market forecast. Paper-thin solar charger fits inside a notebook A By Rich Pell paper thin and ultra-lightweight solar charger from solar design startup Yolk (Seoul) has already raised over $750,000 of its $50,000 goal in its crowdfunding campaign. Designed to be as thin and aesthetically pleasing as possible, the charger, called Solar Paper, is claimed to be “the world’s thinnest and lightest solar charger.” It is thin enough that it can be placed inside a notebook or planner, yet the basic 5-W version is powerful enough to charge a smartphone in 2.5 hours on a sunny day according to the company. Modular in design, Solar Paper can be expanded to handle larger devices by adding new magnetic panels in place. As part of their campaign, the company is offering 5-, 7.5- and 10-W chargers, with two, three or four panels, respectively. The charger works with almost any device that charges via USB and measures 9x19x1.1cm when folded, and weighs 120 grams. It also includes an LCD current meter that displays the amount of current between the charger and device at any time. The first shipments are expected to start in September. 34 Electronic Engineering Times Europe September 2015 www.electronics-eetimes.com


EETE SEP 2015
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