The tandem solar cells are comprised of two multilayered parts that work together to gather a wider range of the spectrum of solar radiation. By using two solar cells with different absorption characteristics, both shorter and longer wavelengths are gathered, resulting in 6.5% efficiency. To date, this is the highest efficiency level achieved by solar cells made from organic materials. Professor Heeger is confident that they can improve the efficiency to a level suited for commercial use. He expects this technology to be on the market in about three years’ time.
The new tandem architecture improves light harvesting and promises to decrease production costs. Professor Heeger explained that the cells can be fabricated to extend over large areas by means of low-cost printing and coating technologies that can simultaneously pattern the active materials on lightweight flexible substrates. According to Heeger, the new solar cells are less expensive to produce due to the deposition of each layer of the multilayered structure by processing the materials from solution.
The material causing the cells to separate and connect is a transparent titanium oxide called TiOx, which is the key to the multilayered system that allows the higher-level efficiency.
The new multilayered material was not developed by accident. In 2000, Heeger won a Nobel Prize in Chemistry (together with Alan MacDiarmid and Hideki Shirakawa) for the discovery and development of conducting polymers. The tandem solar cells utilize semi-conducting polymers from the same class of materials for which Heeger and his colleagues received the Nobel Prize.
TFOT recently covered another development in solar technology – advanced cadmium-telluride (CdTe) semiconductor based solar cells. These new solar cells are also fairly cheap and recently reached 9% efficiency. These numbers are still far from conventional commercial solar panels which can reach efficiency rates of up to about 20% but are considerably more expensive to produce. Other innovative solar technologies covered by TFOT include the Sphelar – a spherical solar cell, the Heliotube – a solar concentrator, and several solar powered vehicles such as the SAUV II solar powered under water robot, the Astrolab – first commercial solar car, the SolarLab – solar powered electric boat, and the Israeli Sunsailor solar UAV.
More information about the new tandem solar cells developed by Heeger and Lee can be found at the University of California, Santa Barbara website.