Thin Film Photovoltaics
Pradeep Haldar, College of Nanoscale Science and Engineering, U.S. Photovoltaic Manufacturing Consortium
The solar photovoltaic industry has grown tremendously over the last decade. Worldwide annual solar cell production increased from 370 MW in 2001 to 27,000 MW in 2010. This rapid growth was driven in part by support programs for solar offered by governments across the world, and in part by the reduction in prices of PV systems.
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Ernst Richter, LNO/Senior Manager; AVANCIS
Reduced costs for direct materials were initially considered one distinct advantage of thin film photovoltaics (PV). Meanwhile, module efficiency and manufacturing costs are the key drivers for its market penetration. Among thin film technologies, copper indium gallium selenide (CIGS) has shown the highest efficiency potential in various applications. Several companies have started large-scale production worldwide, but further improvement in module performance is needed to survive in the competitive PV market. Repeatedly, similarities to the integrated circuit (IC) industry are discussed.[1]
Michael Bauer, Calyxo GmbH
Competitive Position of CdTe
First Solar, as the market leader in thin film photovoltaics, has impressively demonstrated efficiency and production cost benchmarks during the last several years, with average aperture efficiencies in production around 12 percent and decreasing manufacturing costs.[1] Other companies, like Calyxo GmbH, also started successfully to follow this trajectory, with manufacturing costs coming down to <0.80 USD/Wp this year (Figures 1 and 2). The targets are clearly defined for increasing CdTe efficiency levels further in the near future to at least the same range as today’s crystalline silicon module efficiencies. This continued efficiency increase will be a major contributor to further manufacturing cost reductions. Given this, CdTe will remain the cost leader among all other photovoltaic technologies in the future.
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Robert Birkmire, Director, Institute of Energy Conversion;Professor of Material Science, Professor of Physics
Commercialization of CdTe solar cell technology has been dominated by First Solar, established in 1999 using CdTe technology developed by Solar Cells Inc. As the first to demonstrate the “economy of scale” utilizing high-speed/high-throughput manufacturing processes, their success has spawned several competitors that are now close to bringing large manufacturing facilities online.
Torsten Brammer, Consultant, Photovoltaic Research and Consulting
The most prominent challenge in PV is the reduction of the initial investment. But the costs for power from PV also depend on the long-term stability of the components of a PV installation. All PV module technologies can degrade if the individual weaknesses are not considered for the solar cell process, encapsulation and installation. For crystalline silicon, the potential-induced degradation effect gains some attention these days. The Staebler-Wronski effect for amorphous silicon seems to be inherent for this material. Exposure to air and water can cause degradation for CdTe, CIGS, dye-sensitized and organic solar cells. In general, the presence of certain ions in an electric field, the presence of oxygen and water as well as weak bonds can cause a loss in power output of a PV panel.
Tim Young, HyperSolar Inc
The term “concentrated photovoltaics” (CPV) is confusing, even to many in the solar industry. And no wonder – the term is an umbrella one that includes widely varying technologies. To make matters worse, it is often confused with concentrated solar power (CSP) – or solar thermal – which is another animal altogether.
Torsten Brammer, Photovoltaic Research Consultant
When Applied Materials announced the discontinuation of their product SunfabTM, a fully integrated line for manufacturing thin film silicon solar panels, many took this as a clear signal that thin film silicon is not a viable technology. According to analysts, the material to work with is CIGS (new material that promises high efficiencies) and crystalline silicon (mature and dominant market share). CdTe is doing fine anyhow. While there are surely some facts that support this analysis, it is time to see if all facts are considered and to look at thin film silicon more closely.
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Louay Eldada, HelioVolt Corporation
In recent years, thin film photovoltaic (PV) companies started realizing their low manufacturing cost potential, and have been grabbing an increasingly larger market share. Copper indium gallium selenide (CIGS) is the most promising thin film PV material, having demonstrated the highest energy conversion efficiency in both cells and modules. However, most CIGS manufacturers still face the challenge of delivering a reliable and rapid manufacturing process that can scale effectively and deliver on the promise of this material system. HelioVolt has developed a reactive transfer process for CIGS absorber formation that has the benefits of good compositional control and a fast, high-quality CIGS reaction. The reactive transfer process is a two-stage CIGS fabrication method. Precursor films are deposited onto substrates and reusable cover plates in the first stage, while in the second stage, the CIGS layer is formed by rapid heating with Se confinement. High-quality CIGS films with large grains were fabricated on the production line, and high-performance monolithic modules with a form factor of 120 cm x 60 cm were produced. With conversion efficiency levels around 14 percent for cells and 12 percent for modules, HelioVolt started commercializing the process on its first production line.
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Danielle Merfeld, GE’s Global Research Center
Thin film PV continues to capture the attention of the industry with the promise of a departure from the “s-curve” described by the current c-Si PV technology era of solar. Today the range of thin film PV materials is wide and the approaches varied; however, the mantra for success is the same: Use technology to drive high efficiency at low cost. Some approaches are of particular interest based on the opportunity to deliver a high-efficiency product, as evidenced by recent lab-scale records. Others benefit from manufacturing scale and a community of researchers creating advancements on a well-known material system.
Luc Feitknecht, goMicromorph Ltd.
There was a wide-open window of opportunity for thin film solar modules based on amorphous silicon due to the shortage of crystalline silicon wafer material in 2005. The time of the soaring raw-material prices was over in 2010, and the price per watt of solar power plunged lower than expected some years ago. This is good news for the penetration of photovoltaics worldwide. But it presents some difficulty to some manufacturers of solar panels. So why the “crisis” and where to go next? In this article, the discussion centers around amorphous silicon and nanocrystalline silicon tandem solar cells specifically.
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