DuPont will present its broad portfolio of integrated materials and technologies for the photovoltaic (PV) industry at the 20th European Photovoltaic Solar Energy Conference and Exhibition, Barcelona 6-10th June 2005, stand 77. Regarded within the industry as a meeting of the ‘who is who’ of the PV solar branch, the event aims to provide a platform for dialogue and information exchange on bringing market-oriented and sustainable responses to the challenges of the global PV solar energy market. The DuPont portfolio of materials include films, resins for encapsulants, encapsulant films and conductive inks, all designed to improve the lifecycle of photovoltaic modules and reduce the cost per watt of photovoltaic electricity.

PV energy consists in converting light into electrical energy, and is achieved through the use of semiconductors, or photovoltaic solar cells. The cell assemblies are encapsulated into watertight modules for protection from moisture and impacts – the resulting assembly referred to as a solar panel or module. The principle components of a crystalline silicon photovoltaic module are the glass glazing, cross-linked ethylene-vinyl acetate (EVA) encapsulant, the silicon wafers and associated wiring and a protective backsheet. With the exception of the pure silicon encapsulated into EVA, DuPont provides technological solutions for each component, including:

• DuPont™ Elvax® EVA copolymer resins for the encapsulant sheet, or alternatively Surlyn^® ionomer resins,
• DuPont™ Tefzel® ethylene tetrafluoroethylene (ETFE) film for the flexible panels,
• DuPont™ Tedlar® polyvinyl fluoride (PVF) for the weather-resistant backsheet,
• DuPont™ Solamet® photovoltaic materials for the conductive Front and Backside metallizations,
• DuPont™ SentryGlas® PVB and SentryGlas® Plus interlayers to encapsulate solar cells in sheets of laminated safety glass.

Elvax® is used by many solar panel encapsulant sheet producers involved in the manufacture of films for embedding the wafers in panels. It is chosen for its properties such as superior quality and performance stability, ease of processing, low gel levels as well as its impact and puncture resistance. Depending on the demands, Elvax® can be pigmented, filled and cross-linked. Some existing patents describe the use of Surlyn® for PV applications: films made with the ionomer resin offer excellent optical properties, toughness, strength, chemical and UV resistance, as well as the possibility to reach an adhesion to glass. Also Surlyn® is an excellent basis for blending-in various additives.

Tefzel® ETFE films are a substitute for glass in a lamination process to produce flexible PV systems. Used as the top layer of the module, it brings a very high level of light transmittance in the operating frequency range of the solar cells. Tefzel® is lighter and less fragile than glass and shows very little degradation over a long period of time. It also offers excellent mechanical strength and reliability.

Tedlar® PVF films help extend the life and increase the efficiency of delicate PV modules. Virtually since the inception of the PV industry, they have been preferred as the backing sheet for PV modules due to their excellent strength, weather and UV resistance and moisture barrier properties. The most popular backsheet construction is a trilaminate of polyester film between two layers of Tedlar® film. Whilst white is the most popular colour for Tedlar® films when used in PV cells, they are also available in clear or pigmented versions, allowing better aesthetical results and better integration of PV modules in architectural applications.

Solamet® is the DuPont brand name for its comprehensive system of thick film materials used in the construction of PV cells. The thick film metallization pastes have three broad areas of functionality: aluminium pastes to secure a good ohmic contact with the backside (p-side); silver pastes to fire through the ARC (anti-reflective coating) and penetrate into the silicon to achieve a good ohmic contact without shunting; and the silver or silver/aluminium pastes which are soldered to the interconnect ribbon which in turn electrically connects the cells together either in series or in parallel. As the specific properties required of each type of paste can vary significantly, depending on the cell type and pre-processing it has received, DuPont offers several variants of each paste type to match customer processes as much as possible. Currently, PV14x front-side metallization is viewed as a worldwide market standard. The second generation of this type of material is cadmium-free and marketed as the PV15x series, whilst the third generation, to be launched in June 2005, will be lead-free. The aluminium paste PV322, is both cadmium- and lead-free, and has been developed primarily to minimise bowing, which is an increasingly important design criteria as the cell thickness is consistently reduced to remove cost. A co-product PV333, also cadmium-free, is for applications were a thicker oxide layer exists on the back face. For high solder adhesion on to the interconnect ribbon, the family of pastes are complimented by PV583 and PV581, cadmium- and lead-free, which were specifically developed as a silver alternative to the existing standard silver/aluminium PV202.

SentryGlas® PVB and SentryGlas® Plus interlayers are both used to encapsulate solar cells in sheets of laminated safety glass. SentryGlas® PVB has a long history in the laminated glass market and provides excellent adhesion to glass and excellent optics, allowing the laminated glass to pass the required safety standards. SentryGlas® Plus laminates offer increased tear strength and rigidity, as well as higher clarity, and are therefore proposed for PV modules installed in demanding conditions - requiring, amongst other properties, greater strength, impact and structural performance. A special version of SentryGlas® Plus interlayer, designed specifically for the solar cell industry, allows UV rays to pass through to the cells, thus increasing their efficiency.

"DuPont has years of experience in photovoltaic materials development, applications know-how, manufacturing expertise and global market access. By forming a cross-business approach to the industry, we will achieve an increased collaborative intensity towards product research, technology development and technical service. By the same measure, our participation at events such as the one in Barcelona will make it easier for customers to further understand the breadth and depth of our total offering," said Tom Earnest, project leader for DuPont Photovoltaic Solutions. Further information can be found at: photovoltaics.dupont.com.

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