Towards very low-cost mass production of thin-film silicon photovoltaic (PV) solar modules on glass A. Shah a, * , J. Meier b , A. Buechel b , U. Kroll b , J. Steinhauser a , F. Meillaud a , H. Schade c , D. Domine ´ a a Institut de Microtechnique, University of Neucha ˆ tel, Neucha ˆ tel, Switzerland b UNAXIS Displays A.G., Solar Strategic Business Unit, Neucha ˆtel, Switzerland c RWE SCHOTT Solar GmbH, Phototronics, Putzbrunn, Germany Available online 2 September 2005 Abstract Production volume of PV modules increases at >35% per year, but one is yet far from making a global impact on energy supply. One of the obstacles is given by the present high production costs of PV modules. A possibility to reduce costs are thin-film PV modules on glass. The specific option of thin-film silicon is considered. The combination of amorphous and microcrystalline silicon thin films within a tandem solar cell corresponds to a theoretical optimum. In practice, stabilized efficiencies of 10% to 12% have so far been obtained in the laboratory with such tandem solar cells. Silicon being a material with an indirect band gap, its absorption coefficient is relatively low, and therefore light management in the solar cell has to be further optimized. Thin-film silicon can be deposited by plasma-enhanced CVD, as used for AM-LCD displays. The use of modified fabrication equipment from the AM-LCD Display Industry is therefore a promising way to implement low-cost mass production. D 2005 Elsevier B.V. All rights reserved. Keywords: Solar cells; Silicon; Zinc oxide; Plasma deposition 1. Introduction The quest for cost-effective, sustainable energy sources is one of the major concerns of present-day industrial society. It motivates the broad R & D efforts undertaken in the E.U., Japan, USA and in many emerging countries. Because photovoltaic (PV) solar energy can serve as a decentralized source of electricity, it is a key sector in this quest. Even though the increase in worldwide production of PV solar modules is impressive, so far this source of energy only plays a marginal role (Fig. 1). The main reason why PV modules have up to now not been used more extensively is related to their manufacturing cost and, thus, to their market price. Present PV modules are, to a large extent, made of silicon wafers, and here the cost of the wafers themselves is the limiting factor. Fig. 1 also indicates roughly how the price of PV modules has decreased during the last 20 years, (see also [1]), reaching at present average values just between 3 and 4 U.S. $ per W p (peak- Watt); for purchase of large quantities of crystalline silicon PV modules, prices as low as 2.60 U.S. $ per W p are quoted in certain countries. For the large-scale application of Photovoltaics, both for Building-Integrated Photovoltaics (BIPV) in Europe and Japan, as well as for rural electrification and irrigation pumps in emerging countries, like India, Brazil, and China, it is imperative to decrease the manufacturing cost of PV modules further, by a factor of at least 2 to 3, even if one thereby has to accept slightly reduced conversion efficiencies. This has motivated researchers to study, since the early 1980s, different thin-film solar module concepts. In all these thin-film concepts the semiconductor can be deposited directly on low-cost large-area substrates. Furthermore, the cells do not have to be self-supporting; therefore, large-area substrates can be used which are already a part of the 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.07.299 * Corresponding author. Tel.: +41 32 718 3335; fax: +41 32 718 3201. E-mail address: arvind.shah@unine.ch (A. Shah). Thin Solid Films 502 (2006) 292 – 299 www.elsevier.com/locate/tsf