Solar Cells Info

by Aaron Hand, Executive Editor, Electronic Media,
Source: Semiconductor International, Jan 15, 2008
http://www1.semiconductor.net/article/CA6522776.html

Braggone (Oulu, Finland), which develops advanced materials for semiconductor and optoelectronics applications, has signed a joint-development agreement with equipment supplier Beneq (Vantaa, Finland) to offer a turnkey solution for improving the manufacturing efficiency and product performance of solar cells.  Braggone’s innovative antireflective coatings and silicon treatments have been able to significantly reduce reflective properties. Taking this solution from the semiconductor industry to photovoltaics has enabled solar glass reflectivity to be cut from 9.2% to 1.8%, for example, which translates into more of the sun’s energy being captured within the panels.

The partnership with Beneq, to incorporate Braggone’s solution into solar cell manufacturing tools, is just the first among several partnerships Braggone is working on, according to CEO Yrjö Ojasaar, who said that he expects another deal to close later this week. Various tool companies are interested in breaking into the popular solar industry, so matching Braggone’s materials to their tools is one way to do that. Meanwhile, demand for turnkey solutions is rapidly increasing in the capital-intensive photovoltaics industry. “We realized that in order to truly enter the market and make a splash, and get whole lines built around our materials, essentially, we would have to have turnkey solution,” Ojasaar said.

The materials, introduced by Braggone a few months ago, are proprietary polymers that are tuned by modifying hybrid siloxanes. This enables the refractive index (RI) to be optimized to about half what they are for competing antireflective coatings (ARCs) and bottom ARCs (BARCs), which are typically based on SiN materials. Not only are these coatings applied to the solar glass, but can improve solar cell efficiency even further by being applied to the silicon layer as well. Because the silicon surface is also very reflective, a SiN ARC is typically used to cut that reflection. “We’re able to provide a coating that’s twice as effective at cutting reflection,” Ojasaar said, pointing out that solar weighted reflectance (SWR) can be cut from 7.9% for Si3N4 to 3.8% for Braggone’s LUX coating.

Effectively, the coating on the solar glass first helps to deliver more light into the cell. The coating applied to the silicon layer, Ojasaar noted, makes sure the light continues into the active region of the cell rather than getting reflected off the silicon. A layer on the back of the silicon helps efficiencies even further. “A combination of those layers is what significantly increases the efficiency of the cells,” he said.

In addition to increasing cell efficiencies, Braggone’s polymers enable significant reductions in materials and energy costs because they do not have to be applied with chemical vapor deposition (CVD). Instead, they can be applied through spray, slit, spin or dip coating. “This can significantly cut up-front investment in the tool, and cut operational costs of the tool as well,” Ojasaar said.

The solutions partnered with Beneq use a spray coating method made possible by Beneq’s high-capacity two-fluid atomizer, which reduces the droplet diameter to submicron size, enabling high-speed processing. The system is applicable for both crystalline wafers and large, thin-film solar glass substrates, as well as module glass. One tool can produce multiple-RI films and films with both optical ARCs and electrical functions (passivation, hydrogenation) that are needed to boost cell efficiencies.