EXECUTIVE OVERVIEW
The market share for thin-film PV in the US continues to grow rapidly, from 10% in 2003 to ~44% in 2006. Worldwide estimated projections for 2010 thin-film PV production capacity are >3700MW. A 40MW thin-film CdTe solar field currently being installed in Saxony, Germany, costing €130 million equates to an installed PV system price of €3.25/W averaged over the entire project. This is the lowest price for any installed PV system in the world today. Critical research, development, and technology issues for thin-film CIGS and CdTe still remain.
 Figure 1. Thin-film PV market share in US by calendar year. |
Major advances have occurred in the past several years as thin-film photovoltaic (PV) technologies based on copper indium gallium deselenide (CIGS) and cadmium telluride (CdTe) continue to enter the market for various applications. The market share worldwide for thin-film PV in 2006 was less than 6%. However, the market share for thin-film PV in the US continues to grow rapidly and was reported at more than 44% in 2006 [1] (Fig. 1). This number is mainly due to the aggressive growth in the manufacturing capacity of First Solar in Perrysburg, Ohio. In the case of α-Si, Uni-Solar, Auburn Hills, Michigan continues to play a leading role in the US. Both companies report strong growth in 2006, and 2007 estimates should be even better.
We identify several research, development, and technology issues in both thin-film CIGS and CdTe as the technologies scale up to multimegawatt production. For thin-film CIGS absorber layers, about ten deposition processes are currently being developed worldwide. Standardization of the absorber-layer deposition needs to be addressed to help in large-scale thin-film PV manufacturing to lower the unit cost of module production. For thin-film CdTe, back-contact stability offers an opportunity for researchers to make more reliable thin-film PV products.
A number of applications are being pursued using thin-film PV technologies, including building-integrated photovoltaics (BIPV), roof-top applications, and utility-scale applications.
Commercialization of thin-film PV
Several thin-film PV companies in the US and worldwide are actively involved in in the scale-up and commercialization of thin-film PV technologies using α-Si, CIGS, and CdTe. Table 1 summarizes the activities of numerous groups in the US.
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Some 16 companies in the US are pursuing the development and commercialization of α-Si and thin-Si PV products. Clearly, the US leader is Uni-Solar, with an installed capacity of 60MW in 2006. An additional 60MW will come online in 2007, resulting in a cumulative capacity of 120MW. Uni-Solar was supported by the National Renewable Energy Laboratory (NREL) in the technology development of the multijunction solar cells. Applied Materials supplies turn-key projects for the manufacture of single-junction and tandem α-Si/nano-Si (“micromorph”) solar modules. Thus far Applied Materials has completed sales of more than 200MW worldwide in countries such as China, India, Germany, Spain and Taiwan. There are 15 CIGS companies in the US using several deposition methods for the growth of the thin-film CIGS absorber layer. This offers both a challenge and opportunity for these emerging companies. Finally, eight companies are scaling up thin-film CdTe PV technology.
 Figure 2. First Solar’s 90MW thin-film manufacturing plant in the US. |
First Solar is reportedly the global sales leader of all thin-film PV technology companies. They have an installed capacity of more than 90MW in Perrysburg, Ohio for the manufacture of thin-film CdTe power modules (Fig. 2). The company recently started a new facility in Germany with an installed manufacturing capacity of 120MW. An additional 240MW manufacturing capacity in Malaysia is planned for completion in 2009. The total global target of about 450MW by 2009 makes it one of the leading PV companies in the world. Incidentally, NREL awarded the first subcontract to the predecessor company-Solar Cells Inc, OH-for the technology development of thin-film CdTe solar cells and modules in 1991 and has since supported the company in the technology development for commercializing thin-film PV products.
 Figure 3. Thin-film CdTe manufacturing capacity and cost reduction bycalendar year. (Source: First Solar) |
Figure 3 shows First Solar’s manufacturing cost for thin-film CdTe PV modules. As economies-of-scale have been realized, the manufacturing cost has dropped substantially from $2.94/W (6MW) in 2004 to $1.25/W (90MW) at present [2]. The target manufacturing cost is expected to be $0.70/W due to improvements in productivity, module efficiency, and yield by 2012, thus making it potentially price competitive with grid-parity electricity.
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Worldwide, five companies are presently offering commercial thin-film PV CIGS products: Wurth Solar (Germany), Global Solar (USA), Honda (Japan), Showa Shell (Japan), and Sulfurcell (Germany). The production capacity ranges between 5 and 27MW/year. Also, worldwide, about 34 companies are actively developing thin-film CIGS PV technologies. These companies are using about ten different deposition methods for growing the thin CIGS absorber layers, as is shown in Table 2. The absorber layer for commercial products often uses either co-evaporation or the two-stage process such as the deposition of the precursors by sputtering followed by selenization. All companies use Mo as the back contact deposited by sputtering, and the majority use ZnO as the front contact deposited either by sputtering or chemical vapor deposition.
Critical R&D and technology issues
Several critical issues still need to be addressed as emerging and new groups develop thin-film PV technologies. For thin-film CIGS PV technologies, the following six issues are critical for developing low-cost and reliable products:
- standardization of equipment for the growth of the CIGS absorber films,
- higher module efficiencies,
- prevention of moisture ingress for flexible CIGS modules,
- columnar CIGS structures deposited by alternative process for high efficiency cells and modules,
- thinner absorber layers (≤1µm), and<
- CIGS absorber film stoichiometry and uniformity over large areas.
For thin-film CdTe technology, five key issues include the following:
- standardization of equipment for deposition of the absorber layer,
- higher module efficiency,
- back-contact stability,
- reduced absorber layer thickness (≤1µm), and
- control of uniformity over large area.
Applications and production capacity
As thin-film PV technologies mature, installed solar arrays get larger in size. First Solar, along with Juwi Solar, Germany, are installing a 40MW thin-film CdTe solar field in Saxony, Germany. Figure 4 shows the project under construction that is due to be completed by early 2009. Thus far, 6MW of the solar field has been installed. When completed, this will be one of the largest solar fields in the world. The total price of this project is €130 million. Thus, the installed PV system price is €3.25/W, also the lowest installed price for any PV system in the world. Figure 5 shows a thin-film CIGS facade installed on a building by Honda in Japan. The system size is around 80 kW.
 Figure 4. A 40MW thin-film CdTe solar field being built in Saxony, Germany to be completed in early 2009 by First Solar and Juwi Solar. |
It is estimated that by 2010, the production capacity for thin-film PV technologies worldwide will be more than 3700MW. For thin-film PV production capacity, the US is estimated at 1127MW, Japan at 1312MW, Europe at 793MW, and Asia at 472MW.
 Figure 5. Building-integrated thin-film CIGS façade on a Honda building in Japan. |
In breaking news, Sharp recently announced a 1000MW thin-film factory to be built in Japan by 2010. The technology-presumably micromorph multijunction solar modules-will significantly reduce the manufacturing cost of PV, making it potentially more price-competitive with conventional energy sources.
Summary and outlook
Rapid progress is being made by both α-Si- and CdTe-based thin-film PV technologies in entering the commercial market. Several thin-film CIGS companies are also entering the market with power modules. In the US, market share for thin-film was about 44% in 2006 and is expected to surpass Si sales in 2007. Several critical research, development, and technology issues need to be addressed by emerging thin-film PV companies as they plan to enter the market. The projections for worldwide production capacity for all thin-film PV are estimated as more than 3700MW in 2010, with First Solar’s global target at 450MW by 2009 and Sharp’s target of 1000MW by 2010. This economies-of-scale production capacity should substantially reduce the manufacturing price of the thin-film PV products and potentially make solar electricity price-competitive with grid-parity electricity in the not-too-distant future.
Acknowledgments
This work was supported by the US Department of Energy under Contract No. DE-AC36-99G010337. The authors would like to thank the numerous managers, engineers, scientists, technicians whose data are included in this paper. This paper was first presented at the 22nd European Photovoltaic Solar Energy Conference, September 3-7, 2007, Milan, Italy. (Proceedings available at www.photovoltaic-conference.com.)
References
- PV News, March-April, 2003-2007.
- Mike Ahearn, 1st PV Investors Conference, Munich, Germany; April 5, 2007.
Contact Harin S. Ullal and Bolko von Roedern at the National Center for Photovoltaics, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, Colorado 80401 USA; ph 303/384-6486, e-mail harin_ullal@nrel.gov.
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