News

15 July 2009

 

UCLA reports low-cost solution processing for CIGS PVs

A team of researchers led by Department of Materials Science and Engineering professor Yang Yang at the University of California, Los Angeles (UCLA) has developed a low-cost solution processing method for photovoltaic cells based on copper, indium, gallium, selenide (CIGS). These could be produced on a large scale for various applications (including placement on backpacks or clothing), potentially overcoming existing manufacturing difficulties, it is claimed (Thin Solid Films, 7 July issue).

“This CIGS-based material can demonstrate very high efficiency,” says graduate student and first author William Hou. “People have already demonstrated efficiency levels of up to 20%, but the current processing method is costly. Ultimately the cost of fabricating the product makes it difficult to be competitive with current grid prices,” he adds. “However, with the solution process that we recently developed, we can inherently reach the same efficiency levels and bring the cost of manufacturing down quite significantly,” he reckons.

The team reported a copper indium diselenide thin-film solar cell that achieved an efficiency of 7.5%, but this has already been improved to 9.13% in the lab.

“We started this process 16 months ago,” says Yang, who is also a member of the California NanoSystems Institute (where some of the work is being done). “We spent three to four months getting the material to reach 1% and today it's around 9%. That is about an average increase of 1% every two months,” he adds.

Currently, most CIGS solar cells are produced using a co-evaporation vacuum technique (where the active elements — copper, indium, gallium and selenide — are heated and deposited onto a surface in a vacuum). This can be costly and time-consuming, the researchers claim. Using vacuum processing to create CIGS films with uniform composition on a large scale has also been challenging.

The copper-indium-diselenide material created by Yang’s team does not need to go through vacuum evaporation, but is simply dissolved into a liquid, applied and baked. To prepare the solution, the team used hydrazine as the solvent to dissolve copper sulfide and indium selenide in order to form the constituents. The solar cell's absorber layer (which is the most critical layer for performance and the most difficult to control) can then be formed easily by painting or coating the solution evenly onto a surface followed by baking.

“In our method, material utilization is one advantage,” says Hou. “Another advantage is our solution technology has the potential to be fabricated in a continuous roll-to-roll process,” he adds. “Both are important breakthroughs in terms of cost.”

The team's goal is to reach an efficiency of 15-20%. “As we continue to work on enhancing the performance and efficiency of the solar cells, we also look forward to opportunities to collaborate with industry in order to develop this technology further,” says Yang. “We hope this technology will lead to a new green energy company in the US, especially here in California,” he adds. Yang predicts 3-4 years before commercialization.

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