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P-N Junction Innovation Promises Reduced Solar Cell Costs

April 23, 2007

A process developed by electrical engineering and materials science researchers at The University of Texas at Arlington should lower the cost of photovoltaic solar cells and allow the use of more abundant, less expensive and non-toxic materials to convert solar radiation into electricity. These next-generation solar cells should be available for a fraction of the cost of current silicon-based units.

The current solar cell market is dominated by silicon solar cells – approximately 98% of the market. Their high price has been a roadblock to widespread acceptance of solar power generation. Scientists have known that solar cells can be made from materials such as copper indium diselenide, cadmium telluride and copper oxides in addition to silicon. However, indium and cadmium are scarce, expensive and/or toxic, and copper oxides have a serious drawback.

A solar cell is electrically a positive-negative (p-n) junction, which requires both p-type and n-type of the same semiconductor to form. Unfortunately, copper oxides are naturally p-type. Scientists concluded 25 years ago that to make copper oxide solar cells more efficient, they needed to make n-type copper oxides and then p-n junctions of copper oxides: This has never been accomplished due to the difficulty in achieving n-type copper oxides.

Traditionally, p-n junctions are made by diffusion and ion implantation. UT Arlington Electrical Engineering Associate Professor Meng Tao and former Materials Science & Engineering graduate student Dr. Longcheng Wang have developed a process to overcome this problem. They have demonstrated simple methods to make n-type copper oxides and also p-n junctions of copper oxides in solutions.

Since these p-n junctions are made from solution-based methods, they can be made in large quantities, over large areas and inexpensively – all of which are required for a low-cost product. And, while solar cells are the most important application of this technique, this method can also be applied where large-area and low-cost are the main requirements.

This is a first but significant step in a long-term goal to develop an alternative solar cell technology that is cheaper but more efficient than silicon solar cells. A U.S. patent application is in progress and Drs. Tao and Wang are preparing several articles for submission to scientific journals.

“We are actively seeking commercial partners in a development effort,” said Associate Dean of Engineering for Research Dr. Rick Billo. “We believe that leveraging funds as a match for state and federal grants is a great way to obtain an early license for the technology. Through the savings that can be achieved in production costs, the process will allow the partners to gain a dominant marketing position.”

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