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    Dye-sensitized Solar Cells(Environmental Technology)

    Sony has been involved in developing technology for dye-sensitized solar cells for several years. Dye-sensitized solar cells are next-generation solar cells based on innovative technology. Unlike conventional silicon-based solar cells, dye-sensitized solar cells consist primarily of photosensitive dye and other substances. Dye-sensitized solar cells are able to generate electricity by converting energy from light absorbed by the dye. Since these solar cells can be produced from low-cost materials using simple manufacturing processes (such as coating and printing), overall manufacturing expenditures are expected to be comparatively low. Other advantages over silicon-based solar cells include the ability to use a variety of designs and colors and achieve high performance under indoor and low light settings. In addition, changes in the angle at which light hits the surface of the cells have minimal effect on performance. Such dye-sensitized solar cell advantages are expected to expand the range of use for solar cells, which are ideal for a variety of consumer-related applications in which conventional solar cells are unsuitable.

    Sony commenced R&D in this field in 2001. In April 2009, a prototype module based on Sony's unique "Concerto Effect" dye-mixing technology set a world record for a dye-sensitized solar cell by achieving energy conversion efficiency of 8.4%. Subsequently in August 2010, efficiency was further enhanced to 9.9% (*1). Aiming to launch commercial products in the near future, Sony has accelerated efforts to enhance the photovoltaic (light to electric energy conversion) efficiency and reliability of these cells and develop effective manufacturing processes.

    Structure and Principle

    A dye-sensitized solar cell consists of an electrolyte sandwiched between a photoelectrode and a catalytic-electrode (counter electrode). The photoelectrode in this case, is a conductive glass plate coated with porous titanium dioxide to create a layer which can adsorb photosensitive dye molecules. Light energy absorbed in the dye is converted to electricity via solar cell electrochemical properties. In nature, light absorbed by pigment molecules is converted into a different form of energy through photosynthesis. Photosynthesis occurs when chloroplast pigments in leaves convert light energy into chemical energy, which is then used to produce carbohydrates. Because dye-sensitized solar cells also extract electrical energy from light absorbed by pigment molecules (dye), they are also known as "pseudo-photosynthetic solar cells."
    Electrons begin to move when cell is exposed to light Electrons begin to move when cell is exposed to light Electrons travel through transparent electrode and ultimately power light bulb Electrons return to dye molecules

    Sony's Unique "Concerto Effect" Realizes Highest Standard for
    Photovoltaic Performance

    The following four illustrate some of the methods currently used to enhance photovoltaic performance of dye-sensitized solar cells.

    1. Dye molecules can be modified to increase the range of wavelengths across which light can be absorbed.

    2. Light absorption can also be enhanced by increasing the amount of dye molecules adsorbed to the titanium dioxide surface.

    3. Internal resistance can be reduced by modifying the electrode structure and electrolyte.

    4. The efficiency of the solar cell module itself can also be enhanced by increasing the aperture ratio.


    Sony uses all of these approaches to enhance photovoltaic performance. It has also developed its own unique approach, known as the "Concerto Effect." As described below, this method achieves two goals: 1. It expands the light absorption wavelength range and 2. It ensures effective dye molecule adsorption.

    Different dyes absorb light at different wavelengths. By mixing two dyes with different absorption wavelengths, Sony was able to expand the light absorption wavelength range. At the same time, it improved the efficiency by which absorbed light is converted into electricity by increasing the dye molecule adsorption density on the titanium dioxide surface. The combined performance of the two dyes was greater than the sum of their individual performance levels. Because the dyes seemed to resonate together to produce an enhanced effect, Sony dubbed this method the "Concerto Effect."

    • Sony's Unique Concerto Effect Realizes Highest Standard for Photovoltaic Performance


    • Sony used the Concerto Effect to set a new conversion efficiency record of 8.4% using a 150mW module
      Sony used the Concerto Effect to set a new conversion efficiency record of 8.4% using a 150mW module (this result was confirmed by an official agency in April 2009)

    The dye mixture used to create the Concerto Effect consists of two dyes: black dye and D131. When black dye is used alone, its molecules tend to cluster together to form aggregates. This prevents efficient photoelectric conversion by slowing the passage of electrons from the dye molecules to the electrode, and by hindering the flow of electrons from the dye molecules into the titanium dioxide. However, when black dye and D131 are mixed together, the D131 molecules prevent the black dye from forming aggregates and both dyes are adsorbed effectively while avoiding aggregate formation.

    In many cases, dye mixtures reduce rather than improve photovoltaic performance because they fail to provide effective routes for carrying electrons to the electrode. However, the mixture used in creating Sony's Concerto Effect provides highly-efficient routes for transporting energy from the light absorbed by each dye to the electrode. In addition to increasing the light absorption wavelength range, this approach also improved the overall efficiency with which absorbed light was converted into electricity. As a result, Sony's prototype dye-sensitized solar cell module set a new world record (*1) with a photovoltaic conversion efficiency of 8.4%. Subsequently in August 2010, efficiency was further enhanced to 9.9% (*2).

    *1As of June, 2009. References: M. A. Green, K. Emery, Y. Hishikawa and W. Warta, Prog. Photovolt: Res. Appl. 17, 320 (2009).
    References: R. Y. Ogura; S. Nakane; M. Morooka; M. Orihashi; Y. Suzuki and K. Noda. APL 94, 073308 (2009)
    *2According to measurements carried out by the National Institute of Advanced Industrial Science and Technology.


    Potential Applications

    • The concept for these Hana Akari (literally flower light) solar powered lamps comes from tradition
      The concept for these Hana Akari (literally "flower light") solar powered lamps comes from traditional Japanese paper lanterns

    These lamps generate their own electricity to produce light via dye-sensitized solar cell lampshades. Dye-sensitized solar cells can be created using various colors of dye. Such freedom in choice of colors gave designers a great deal of leeway in creating color schemes and patterns for these solar lampshades. The cells are manufactured by coating the photoelectrode glass substrate with titanium dioxide and subsequently screen-printing various patterns on top of this.

    • Sony is working to develop large-size panels
      Sony is working to develop large-size panels

    A key functional advantage of this technology is the fact that dye-sensitized solar cells are more sensitive than crystalline silicon-based cells to visible light, including limited natural light on cloudy days, and artificial light produced by interior lighting. These cells are also more sensitive to light striking the panels at a shallow angle. Such characteristics enable dye-sensitized solar cells to reliably generate electricity under a variety of conditions.

    These advantages are expected to expand potential solar cell applications to include a wide range of consumer-related markets for which conventional silicon-based cells provide only minimal benefit such as walls, windows, interior products and interior décor.

    Mass-Production Technology & Improving Reliability

    Several types of solar cells already exist in today's market. Nevertheless, certain types of next-generation solar cells featuring specific advantages are being viewed with particular interest around the world. Dye-sensitized solar cells represent a promising next-generation solar cell technology which has achieved significant progress in recent years. Further work will be needed to take this technology to the next level in terms of photovoltaic performance and manufacturing methods. In addition, engineers and others will need to begin studying numerous technological aspects yet to be explored. Manufacturing technology for dye-sensitized solar cells encompasses a number of fields in which Sony possesses advantages due to its rich storehouse of technological knowhow. Examples include material coating methods and electrolyte containment systems created over years of developing other products such as rechargeable lithium ion batteries and magnetic tape.

    Sony aims to develop the related mass-production technology and create useful applications in the near future and will continue to improve the photovoltaic performance and reliability of dye-sensitized solar cells by developing new material and device technologies, including dyes, electrodes, electrolytes and module structures.

    Reference
    R. Y. Ogura, S. Nakane, M. Morooka, M. Orihashi, Y. Suzuki and K. Noda; APL 94, 073308(2009)





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