Key Solar Cell and Module Material Trends to Watch in 2010


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Key Solar Cell/Module Material Trends to Watch in 2010

By Mike Corbett and Mark Thirsk, Linx Consulting, LLC (March 15 2010)

The PV industry is far stronger at the end of 2009 than it was at the end of 2008, and will likely be stronger still in 12 months. In 2010, the dynamics of the solar industry will still be policy driven. However, the need to reduce carbon emissions, decrease reliance on foreign fuel supplies, and create jobs will foster support for solar energy around the world. Materials innovation and materials-driven solutions will support continued industry growth over the next year.

Key Cell Material Trends to Watch in 2010

Texturization and Cleaning

Balancing the introduction of novel functional chemistries with cost considerations will be a challenge. Wet processes are key determinants of cell efficiency. By forming a surface that entraps light for conversion, and determining the quality of the silicon surface wet processes can be a large influence in the final cell efficiency. However, ultraclean processes, aggressive chemicals, and automated handling are all common in semiconductor processing, but carry costs for the pure chemistry, safety precautions, and eventual disposal of the used etchants.

Metallization

Printed paste, despite the cost of the base metal powders used, represents a remarkably cheap and efficient way of putting metal where it is needed. As cells develop limits of the screen printing technology (edge acuity, aspect ratio, etc.) become the gating factors on the pattern. Various techniques have been introduced aimed to increase aspect ratio and line acuity, and improved pastes formulations are continuously being evaluated to improve conductivity, and formation of ohmic contacts to various doping levels and types of silicon.

Selective Emitters

The drive to squeeze more efficiency out of the cell the search to reduce the resistance at the metal / silicon contact, while maintaining the optimum doping profile in the photocell has received considerable attention. To many semiconductor professionals, this is best achieved with multiple masking steps and diffusion processes. However, in the relentless push to avoid additional cost, multiple routes to reduce processing steps and achieve the same result have been developed, mainly by turnkey production line manufacturers. Techniques to achieve these selective emitters include the following approaches, among others:

  • Etching back highly doped silicon from open areas while leaving the grid line areas untouched.
  • Laser doping the emitter areas, and using the paste firing to drive in a light diffusion from spray deposited phosphoric acid.
  • Differential doping through laser patterned oxide masks prior to standard processing.
  • Printing dopant pastes over emitter areas that dope n++ areas.
  • Using etchant screen print pastes to open windows in an oxide before standard deposition.

Key Module Material Trends to Watch in 2010

Encapsulants

Thermoplastic encapsulants offer reduced laminator process times as the materials do not need a hold time at temperature to crosslink. This reduced processing time improves throughput and potentially offers capital costs savings due to a reduced number of laminators required. Critical in the introduction of thermoplastic encapsulants are the material properties of the materials, and their ability to meet performance characteristics as defined by EVA. Novel encapsulants using PVB, Olefins, Urethanes and Silicones have all been announced and multiple manufacturers have products in development. Certifications are progress with international test organizations, and these materials will compete in both thin film and c-Si modules.

Figure 1 illustrates the output from a sensitivity analysis. It details the impact of improving module curing time and module curing cost.

Figure 1. Impact of Improving Module Curing Time and Module Curing Cost

Source: Linx Consulting - Chemicals & Materials for Solar Cells and Modules, March 2010

Backsheets

Japan was one of the first countries to promote PV installations with subsidies, and a strong domestic industry developed in the 1980s. c-Si modules used a laminated PET backsheet that offered good insulation, but that degraded with exposure to UV light and harsh environments. As a consequence, module lifetimes were guaranteed at only 10 years. In contrast, most modules for commercial and residential use in Europe and North America are expected to last significantly longer, and the use of fluoropolymer materials, mainly PVF became common. As demand grew, the limited supply of PVF, and the search for alternative materials have brought in PVDF and other fluoropolymer alternatives in backsheets. The highly customizable nature of backsheets is leading to a large number of module maker specific products that incorporate different materials. Key for material acceptance is not only certification by LU, TUV or IEC, but the ability to supply the very large film volumes that are needed if materials are adopted by leading module makers.

Front Sheets

For both thin-film and c-Si modules a key material is the front sheet. While glass is a cheap, plentiful material, glass front sheets are technically complex, with molded surfaces to aid light capture, aesthetics, and module durability, and narrow composition specifications to meet transparency needs.

Forecast

As Figure 2 below, shows our forecast for materials market growth to 2015. The overall market will grow from $2,455 million in 2009 to $8,275 million in 2013. The market growth forecast is reliant on a “business as usual” subsidy environment. Alternative scenarios are presented in the Linx AEI Consulting report “Advanced Materials for PV Cells and Modules, 2010” published in February 2010.

Figure 2 – Materials Demand Forecast for PV Cells and Modules

Source: Linx Consulting - Chemicals & Materials for Solar Cells and Modules, March 2010


The growth opportunities identified here are all important contributors to the effort to make the PV industry commercially viable without subsidy, and thus once successful, self-sustaining. If materials suppliers can collaborate with equipment makers and process developers to bring these innovative processes to market, the point where PV competes with utility-supplied power will only come sooner.

Information in this article is based on the new Chemicals & Materials for Photovoltaic Cells and Modules 2010 report, which outlines market opportunities available to chemicals and materials suppliers as a result of strong volume growth in addition to technology-driven opportunities to deliver progress towards lower cost. It examines emerging materials requirements in solar cell and module production, and quantifies the global markets for advanced chemicals and materials.

The report covers polysilicon and wafering, process chemicals, conductive pastes and inks as well as metallization materials, specialty gases and dopants, functional polymers including encapsulants, backsheets, and glass substrates. In order to forecast chemicals and materials demand, the report also provides solar demand by cell type, with perspectives on crystalline silicon, amorphous silicon, tandem cells, CdTe and CI(G)S.

For additional information and for ordering, please visit http://www.semi.org/en/Store/MarketInformation/Photovoltaics/ctr_029966