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Long-term Stability of Polymer Solar Cells

written by: Aggeliki K.•edited by: Lamar Stonecypher•updated: 1/31/2011

The article describes the latest advances regarding the improvements in efficiency and lifetime of polymer solar cells, and the problems that need to be overcome in order for them to become commercially available.

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    Polymer Solar Cells in General

    Conducting polymers were discovered back in 1976 by A. Heeger and A. MacDiarmid. The first step was to dope these polymers in order to produce insulators, conductors, and semi-conductors. The idea to use these materials in solar cell technology came in 1992.

    The advantage of polymer solar cells or organic photovoltaic cells (OPVs) is that they are based on the extraordinary properties polymers have. These materials are light, flexible, inexpensive, and easy to produce. All these characteristics make these materials ideal for industrial and home-based solar cell applications that can be incorporated into fabrics and building-integrated PVs.Examples of organic photovoltaic materials svg  The production and operation of polymer solar cells is a "greener" process than that of conventional silicon cells.

    Polymers are also used in solar-control glazing products (polycarbonate sheets) to protect buildings or as a means of transport from the excessive heat and harmful solar rays while allowing high transparency to visible light. Polymer solar glazings are finally available at a low cost due to the advances in this area as well.

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    Current Status

    Two of the leading companies in the field of organic photovoltaics are Konarka and Solarmer Energy.

    Konarka is mainly an OPV manufacturer that basically supplies other companies for multiple solar cell applications. The company reached a world record of 6.4% for OPV efficiency in May 2009.

    Solarmer Energy on the other hand, achieved three successive world records in 2009 – 6.8 %, 7.6 % and 7.9 % that were all certified by the National Renewable Energy Laboratory. In May 2010, they achieved a world record of 8.13 %.

    Lately, Konarka managed to achieve 8.3% efficiency, a fact that was announced and confirmed by the National Renewable Energy Laboratory in December 2010. The company has already installed polymer solar cells on the exterior of large buildings in Florida and bus stations in San Francisco. They also plan to use the new technology in the production of consumer goods such as luggage and umbrellas.

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    Difficulties and Problems to Overcome in OPV technology

    OPV technology is still in the early stages of development. Despite the advantages that it already has or may have in the future, the efficiency is still very low compared to the conventional PVs such as silicon cells that reach an average efficiency of 14 to 18%. Some of them can even reach the efficiency of 20%. Another drawback of polymer solar cells lies in their short lifespan, which increases the cost of use and production.

    The image below shows the structure of a polymer solar cell. In order to deal with the low efficiency and short lifetime of current OPVs, researchers are constantly testing new materials, structures, and combinations. Their goal is to achieve the long-term stability of polymer solar cells that will make them a commercially viable solution for cell technology.

    Polymer solar cell technology will probably become extremely competitive during the next several years. The next target of OPV manufacturers is to reach 10% efficiency by the end of 2011. The efficiency increase is absolutely necessary if polymer solar cells are to dominate the future solar cell market.

    Structure of Multilayer Organic Photovoltaic Cell