Photovoltaics and How to Avoid the Fall of Icarus

The PV industry is a huge success story today, with new companies shooting up like mushrooms and big companies shifting their gears towards this Holy Land of dollars. A crucial factor enabling this double-digit yearly growth is the incentives of European countries and, in particular, of the German government.

Thanks to this success, these incentives will be cut down at a faster pace than originally anticipated. To maintain a strong and sustainable PV market and ensure returns on the large investments that PV companies have made worldwide, grid parity has to be reached as soon as possible.

Without continued technological improvements, the PV industry may fall from its current heights like Icarus when he got too close to the sun. Here are some thoughts on how to improve:

For both bulk silicon solar cells and thin-film solar cells, it will be key to achieve a rise in solar cell efficiencies at an accelerated pace and a cost reduction. This does not necessarily imply immediate revolutionary changes. For bulk solar cells for example, the efficiency can be increased by contacting of shallow emitters and decoupling of front and rear side processing. These technologies are available for development and deployment by the industry. It will be crucial to guarantee the reliability of these solutions.

In general, an accelerated transfer of new technologies from lab to industry is key to maintaining a stable market after the incentives have faded out. Within this respect, it is important that interaction between research institutes and companies is increased and reinforced. Suitable business models for cooperation will have to be worked out. One such example is imec’s affiliation program in which different companies work together to develop new generic technologies to increase efficiency and reduce cost of bulk and thin-film solar cells. The sharing of risk and cost makes it an attractive business model to partners.

From a research point of view, new themes that will be important in 2011 are the study of new PV materials. These are necessary to replace materials that are suspected to be hampered by a limited supply in the future. If we want to be ready when the time of shortage comes, we have to start studying the possibilities today. For example, think of the replacement of silver contacts by copper contacts: if we want to develop a reliable solution to this problem, we have to start studying the possibilities now.

Imec is working to reduce the thickness of the active silicon layer from 150μm down to 40μm. This will substantially lower the production cost of crystalline Si solar cells.

To reach efficiencies of more than 20% on such large-area thin wafers, imec has introduced alternative back-side dielectric stacks using a PERL-style (passivated emitter and rear local back surface field) passivation, and interdigitated back-side contacts (i-BC), both in an industrial process flow.

We also investigate the integration of these new cells in modules, as reduced wafer thickness will impose specific integration requirements. And we work on and assesing the reliability of the cells, as the cells will need a guaranteed lifetime of up to 25 years.

Imec has also developed epitaxial thin-film (<20μm) silicon solar cells grown on low-cost silicon carriers. The process to fabricate such epitaxial thin-film cells on low-cost silicon carriers is generically similar to the bulk process, so an epi-process can be implemented with limited equipment investment in existing manufacturing lines.

Given the guarantees on lifetime and stability of PV modules, it should be emphasized that no technological innovation in photovoltaics can make it without a thorough assessment of reliability. However, with a well-thought choice of R&D topics, a large focus on reliability of new technologies, and an accelerated transfer of lab results to the industry, I believe PV industry can continue its growth path even within the context of rapidly decreasing incentives, and remain a booming business.

Jef Poortmans is the Program Director of the Strategic Programme SOLAR+ at IMEC.

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