PAPER PRESENTED AT 26TH EU PVSEC, HAMBURG, GERMANY 2011 Crystalline thin-foil silicon solar cells: where crystalline quality meets thin-film processing Frederic Dross * , Kris Baert, Twan Bearda, Jan Deckers, Valerie Depauw, Ounsi El Daif, Ivan Gordon, Adel Gougam, Jonathan Govaerts, Stefano Granata, Riet Labie, Xavier Loozen, Roberto Martini, Alex Masolin, Barry O’Sullivan, Yu Qiu, Jan Vaes, Dries Van Gestel, Jan Van Hoeymissen, Anja Vanleenhove, Kris Van Nieuwenhuysen, Srisaran Venkatachalam, Marc Meuris and Jef Poortmans IMEC vzw, Kapeldreef 75, B-3001 Heverlee, Belgium ABSTRACT Crystalline Si (c-Si) technology is dominating the photovoltaics market. These modules are nonetheless still relatively expensive, in particular because of the costly silicon wafers, which require large thickness mostly to ease handling. Thin-film technologies, on the other hand, use much less active material, exhibit a much lower production cost per unit area, but achieve an efficiency still limited on module level, which increases the total system costs. A meet-in-the-middle is possible and is the object of this paper. The development of c-Si thin-foil modules is presented: first, the fabrication of the active material on a glass module and then the processing of the Si foils into solar cells, directly on module level. The ac- tivity of IMEC in this area is put into perspective with regard to worldwide research results. It appears that great opportunities are offered to this cell concept, although some challenges still need to be tackled before cost-effective and reliable industrial production can be launched. Copyright © 2012 John Wiley & Sons, Ltd. KEYWORDS crystalline Si; thin film; low-temperature processing; polycrystalline Si; kerf-free wafering; epitaxial solar cells; light trapping; silicone; reliability; layer-transfer *Correspondence Frederic Dross, IMEC vzw, Kapeldreef 75, B-3001 Heverlee, Belgium. E-mail: frederic.dross@imec.be Received 29 May 2011; Accepted 4 October 2011 1. CONTEXT AND CONCEPT With approximately 85% share in 2010, crystalline sili- con (c-Si) technology is dominating the photovoltaics (PV) market. This fact can be attributed to several factors: • Crystalline Si material displays a higher minority- carrier lifetime and a longer minority-carrier diffusion length than, for instance, amorphous Si, making it possible to reach efficiencies as high as 25% [1]. • Si is abundant and its supply is not expected to limit the production of Si-based solar cells even in the most aggressive scenarios of terrawatt peak (TW p ) produc- tion per year [2]. • Si is non-toxic and is therefore not subject to ethical questions regarding the reconditioning process at the end of the module life cycle. • Module manufacturers are required to guarantee a stable performance of the modules over several decades; Si solar cells are stable over time, and the module technology has proven its reliability through many years of field experience. • Thanks to continuous effort of production cost reduction, the c-Si solar cell industry managed to maintain a learning curve (decrease of cost per watt peak when production volume doubles) of more than 20% since the 1970s [3]. The volumes reached in the early years 2010 make it now more and more difficult for a new coming technology to compete with the mainstream. Despite these crucial assets, the technology still holds a strong potential for further cost reduction. The cost of a module is dominated today by the substrate cost, where the 180 mm of expensive material is mostly used to PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS Prog. Photovolt: Res. Appl. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/pip.1238 Copyright © 2012 John Wiley & Sons, Ltd.