Transparent conducting oxide deposition techniques for thin-film photovoltaics

By Volker Sittinger, Senior Scientist, Large Area Coating Department, Fraunhofer IST; Wilma Dewald, Junior Scientist, Magnetron Sputtering Group, Fraunhofer IST; Wolfgang Werner, Engineer, Fraunhofer IST), Braunschweig, Germany; Bernd Szyszka, Head of the Department of Large Area Coatings, Fraunhofer IST; Florian Ruske, Senior Scientist, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Highly conductive transparent films are of significant interest in the field of thin-film photovoltaics. The solar cell type defines the necessary properties of the TCO used, as, besides the obvious qualities of transparency and conductivity, stability and morphology are important. The most significant properties of these aspects for front contacts in amorphous/microcrystalline silicon tandem, CIGS and CdTe solar cells are presented in this paper. Commonly used deposition techniques like CVD and sputter technology are described herein, focusing on particular techniques like SnO2:F and ZnO:B (CVD) and ZnO:Al (sputtering). New developments of deposition methods are also discussed.

High productivity combinatorial study of wet chemical texture etch of sputter deposited Al-doped ZnO

By Nitin Kumar, Program Manager, Intermolecular, Inc.; Guizhen Zhang, Process Engineer, Intermolecular, Inc.; Nikhil Kalyankar, Process Engineer, Intermolecular, Inc.; Minh Anh Nguyen, Process Engineer, Intermolecular, Inc.; Jian Li, Process Engineer and Project Manager, Intermolecular, Inc.; Henry Yang, Member of Technical Staff, Intermolecular, Inc.; Zhi-wen Sun, Principal Scientist, Intermolecular, Inc.

This paper presents fluorescence detection as a new tool for the investigation of the degradation of EVA. The superior sensitivity of the setup contained herein allows an early assessment of the changes of the EVA after only 20 hours of damp-heat exposure. A newly developed scanning system allows the spatially resolved inspection of entire PV modules. Degradation of the encapsulants was detected after two years’ outdoor exposure, as was the effect of cracks in c-Si cells, which coincide well with cracks made visible by electroluminescence.

Atmospheric deposition techniques for photovoltaics

By Heather A.S.Platt, Senior Scientist, National Renewable Energy Laboratory; Maikel F.A.M. van Hest, Senior Scientist, National Renewable Energy Laboratory

With the never-ending need to reduce production costs, interest in atmospheric deposition techniques is steadily increasing. Even though atmospheric deposition is not new to photovoltaics, and in some cases is actually required to get the best cell performance, many of the fabrication processes for photovoltaic cells are vacuum-based. Due to the diversity in atmospheric deposition techniques available, there are opportunities for applications in thin film and patterned deposition. This paper discusses some of the deposition techniques and their applications, benefits and drawbacks.

Ramping a novel cadmium telluride thin-film solar photovoltaic module production process

By Kurt Barth, Founder, Abound Solar; Mark Chen, Director of Marketing, Abound Solar

Thin-film solar photovoltaic technology offers the benefits of low-cost and high-volume production. Yet numerous thin-film PV startups have struggled in their efforts to commercialize complex, expensive production technologies, as production ramps have taken longer than expected, and venture capital and other sources of funding have run dry. This article describes a proprietary cadmium telluride (CdTe) thin-film module production process commercialized by Abound Solar: heated-pocket deposition (HPD) of the semiconductor layer, and the replacement of a traditional lamination process with a novel edge seal. The simple production process has resulted in a fast ramp of module efficiency and throughput. The paper will also describe how the process also results in fast throughput, high yields, and low manufacturing and capital equipment costs.

Applied knowledge management for complex and dynamic factory planning

By Martin Kasperczyk, Project Manager, Oerlikon Solar AG; Fabian Böttinger, Project Manager, Fraunhofer IPA; Marcus Michen, Project Manager, Fraunhofer IPA; Roland Wertz, Project Manager, Fraunhofer IPA

This paper describes the functionality, applicability, and the development of dependency maps which are the basis for standardized information exchange between responsible parties during the fab design process. Examples and experiences are related to the solar industry; however this generic approach may be applied to a wide range of different industry sectors with similar challenges. The aim is to provide a guideline for realizing a fab design of dynamic and complex production systems. Its main benefit is a higher degree of transparency regarding dependencies within the production system, which results in a reduction of risk for incorrect planning. In addition, it enables the factory designer to execute the fab planning process and further continuous improvements for achieving respective targets.

Forecast for thin-film PV equipment market calls for sustainable growth

By John West, Managing Director, VLSI Research, Bedford, UK

The demand for equipment used to manufacture solar photovoltaic solar cells and modules has grown at an explosive rate over the past five years, and the fastest-growing segment has been for systems used to manufacture thin-film cells and modules. In 2009, demand for this type of equipment reached US$1.9 billion, up from US$0.1 billion in 2004, representing an astonishing 80% compound annual growth rate over the period. However, as with the rest of the industry, 2009 saw sales flattened and the business model change from one of rapid growth to that of sustainability. The result of this transition has been some consolidation, with several major equipment vendors strengthening their position through acquisitions. The outlook for 2010 calls for sales of thin-film production equipment to recover and continue growing at a compound annual growth rate of around 15% over the next five years (see Fig. 1).

Glass washing challenges in thin-film PV production

By Eric Maiser, Managing Director, VDMA; Iris Minten, Public Relations/Online Communication, Bystronic glass; Karl-Heinz Menauer, Managing Director, ACI-ecotec; Egbert Wenninger, Head of the Grenzebach Group Glass Technology Sales Division, Grenzebach Maschinenbau

Thin-film module production has proven itself as a forerunner in the race to drive down costs for photovoltaics. The type of semiconductor material used is the most differentiating factor for thin-film photovoltaics, playing the decisive role for determining which core processes are employed and what type of equipment is used. This explains why discussions related to thin-film costs and technologies usually focus on the semiconductor type. However, the effects of glass production, processing and handling are often underestimated: factors such as scaling, yield, unit cost and total cost of ownership of the equipment are defined by the glass-production side of the industry. This paper discusses the challenges faced in glass washing and handling in thin-film PV production.

Taking thin-film technology closer to the lowest possible manufacturing cost

By Hriday Malik, Freelance Writer

It is widely acknowledged that, without government subsidies, solar power still cannot compete effectively with conventional sources of electrical energy. As the industry strives to make solar electricity affordable and as a viable alternative to fossil fuels, solar power technology companies are diligently moving towards reducing the manufacturing cost for solar modules. In the case of thin-film solar cells in particular, as a benchmark, the cost of for solar power must be reduced for it to be competitive or to attain grid parity. This paper presents a number of opinions from industry leaders on how best to decrease this vital cost.

Scaling single-junction a-Si thin-film photovoltaic technology to the next level

By Mohan K. Bhan, Vice President of Engineering, Moser Baer PV Technologies India Limited; Rahul Kapil, Moser Baer PV Technologies India Limited; Indu Shekhar Bajpai, Moser Baer PV Technologies India Limited; Rajesh Kumar, Moser Baer PV Technologies India Limited; Vineet Jain, General Manager of Operations, Moser Baer PV Technologies India Limited; Sudheer Kumar, General Manager of the PV Solutions Group, Moser Baer PV Technologies India Limited

The recent photovoltaic industry shakeout which started around Q3 2008 has faced the overcapacity, credit crunch, and economic crisis that significantly declined the average selling price by 50 - 65%, including the price of thin-film photovoltaic modules. The changing business environment has put significant pressure on all PV manufacturing technologies but more candidly on amorphous silicon thin-film single-junction module manufacturers to advance and scale up the device efficiency and aggressively drive cost reduction. This paper outlines the approach taken at Moser Baer Photovoltaic Technologies India Limited (PVTIL), including process optimization and device management strategies, to enhance the module efficiency (total area) of the single-junction amorphous silicon quarter size, 1.43m2, substrate as manufactured using Applied Materials’ SunFab line.

Using novel spectroscopy and spectrometry techniques for the quantitative analysis of photovoltaic thin films and materials

By Fuhe Li, Director of Advanced Materials and Thin Films, Air Liquide–Balazs NanoAnalysis; Scott Anderson, Director of Laboratory Operations, Air Liquide–Balazs NanoAnalysis

Chemical stoichiometry along with depth profiling and metallic contamination is of considerable interest for photovoltaic thin films. Conversion efficiency can be affected for example if primary components, e.g. Cd and Te, are not present at proper ratios. Moreover, amorphous silicon can vary substantially between sources and deposition technique, and qualitative comparison of trace metallic contaminants may not be sufficient to ensure final thin-film quality. This discussion presents data from atomic emission and mass spectrometry techniques that quantitatively and accurately describe both bulk and trace elemental compositions in photovoltaic materials, various thin-film matrices, and the final thin-film cell and module.

Comparison of different ceramic Al-doped ZnO target materials

By Volker Sittinger, Senior Scientis, Large Area Coating Department, Fraunhofer IST; Wilma Dewald, Junior Scientist, Magnetron Sputtering Group, Fraunhofer IST; Wolfgang Werner, Fraunhofer IST; Bernd Szyszka, Head of the Department of Large Area Coatings, Fraunhofer IST; Florian Ruske, Scientist, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Highly conductive transparent films are of significant interest in the field of thin-film photovoltaics. ZnO-based films in particular have attracted much interest due to the low cost of materials with good film properties for CIGS and a-Si/µc-Si solar modules. Investigations have been ongoing at Fraunhofer IST into ceramic ZnO:Al2O3 targets from different manufacturers. This paper presents a comparison of target material, sputter characteristics and film properties of ZnO:Al. Sputter characteristics are in this case determined by voltage and current data showing arcing rates at different power loads and process pressures. ZnO:Al films are deposited by DC magnetron sputtering with various deposition parameters (e.g oxygen flow, total pressure, sputtering power and substrate temperature) and investigated with respect to optical and electrical properties. A correlation between film properties, sputter characteristics and target material can therefore be determined. As it appears that arcing has the biggest influence on film properties, the ceramic target material can be optimized for minimal arcing.

Photographic electroluminescence analysis of CIGS thin-film solar modules

By Uwe Rau, Director, IEF5-Photovoltaik, Forschungszentrum Jülich; Thomas Kirchartz, IEF5-Photovoltaik, Forschungszentrum Jülich; Anke Helbig, Institut für Physikalische Elektronik, Universität Stuttgart; Jürgen Werner, Director, Institut für Physikalische Elektronik, Universität Stuttgart; Raymund Schäffler, Product Manager, Technology and R&D, Würth Elektronik Research GmbH

This paper, the third in a series covering cost of ownership (COO) studies for photovoltaics [1], examines the need for metallization of silicon-based solar cells and how it has evolved over the past few years. The technologies and techniques that are being developed for this part of cell manufacturing in the foreseeable future are also discussed. The paper will conclude with a COO case study using the DEK Solar PV3000 as an example.

Rise of thin-film technologies

By Denis Lenardič, PV Resources, Jesenice, Slovenia

Until the year 2002, wafer-based crystalline silicon solar cells were almost exclusively the solar cell technology used for large-scale power plants. Since then, steady growth in the market share for thin-film technologies has been observed, although crystalline silicon technology still remains the most important solar cell technology used in large-scale PV power plants. The market share of thin-film modules, especially CdTe modules, has been continuously increasing in recent years, most notably in the German market. However, other countries like Spain, the USA, Italy and France have seen some large-scale CdTe-based modules being installed in power plants recently.

Understanding moisture ingress and packaging requirements for photovoltaic modules

By Arrelaine A. Dameron, Postdoctoral Researcher, National Center for Photovoltaics, NREL; Matthew O. Reese, Postdoctoral Researcher, National Center for Photovoltaics, NREL; Thomas J. Moricone, Research Technician, PV Module Reliability Group, NREL; Michael Kempe, Scientist, PV Module Reliability Group, NREL

Outside of the challenges of fabricating state-of-the-art photovoltaic devices, further care must be taken to package them such that they can withstand environmental conditions for an accepted lifetime of 20-plus years. Moisture ingress is a big adversary to hermetic packaging. The diffusion of water through barriers and edge seals can be minimized by careful choice of materials and package/barrier architecture. However, at present, there exist no solutions for extremely water-sensitive materials for flexible applications. Presented in the following is a review of the physics of permeation, the means of measuring permeation, current architectural strategies for semi-hermetic packages, and a brief evaluation of some common encapsulant materials.

Characterization and monitoring technologies for CIGS

By Theresa M. Friedlmeier, SEM, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW); Wolfram Witte, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW); Wolfram Hempel, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW); Richard Menner, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)

Among the various thin-film solar module options available, CIGS is especially interesting as it exhibits the highest efficiency potential. These chalcopyrite-based solar cells are manufactured on glass or flexible substrates using various thin-film coating methods for each layer. The central CIGS absorber layer is deposited by co-evaporation, selenization of elemental layers, and other methods. In order to achieve highest quality and reproducibility, the absorber properties must be properly monitored and characterized. In this contribution we shed some light on the most important analysis methods used for CIGS solar cell research, development, and production such as x-ray fluorescence, surface analysis, and Raman spectroscopy.