Paint-on solar cells are coming closer to reality every year. Recent research on the use of anatase titanium dioxide in solar cells has once again raised the photovoltaic efficiency bar – now to 15 percent – for solar cells, suggesting that it may yet become a basic block in building-integrated photovoltaics (BIPV).
While research in dye solar cells has been ongoing for decades as a less expensive alternative to silicon solar cells, a new consortium of players is aiming to make TiO2-based BIPV commercially available within a few years. Global research on TiO2-based solar cells include applications on glass, metal, flexible plastic and other surfaces. Unlike silicon-based solar cells, designed to operate in full sunlight, dye solar cells operate well in lower-light conditions.
The latest efficiency breakthrough was published in "Nature" magazine in July by the so-called “father” of dye solar cell development, Michael Grätzel, a research professor at Ecole Polytechnique Federale de Lausanne (EPFL), in Switzerland. The efficiency of different types of materials being researched to produce solar cells ranges from a single-digit to 40-plus percent efficiency, at very different costs. His work includes the discovery that titania molecules ranging between two nanometers and 50 nanometers provided the best conductors for electrons in the cells.
Similarly, a “major technical breakthrough” occurred in May with solid state dye solar cell (DSC) technology, which “catapulted to 11.3 percent efficiency at full sun,” said Angela Geary, the brand manager for Dyesol Inc. based in Queanbeyan NSW, Australia. She noted that “by comparison, performance was at just five percent in 2010 and significantly lagged the traditional liquid DSC material set performance.”
To help commercialize this work, Grätzel is cooperating with Dyetec Solar, a Toledo-based joint venture between parent Dyesol and Pilkington Glass, to come up with a large format coated glass solar cell for use in buildings and automobiles. Pilkington is a subsidiary of Nippon Sheet Glass, of Tokyo. Dyetec has received a $950,000 grant from the Ohio Third Frontier Commission, which fosters new technology in the state.
A new $16 million investment in Dyetec is being considered by National Titanium Dioxide, or Cristal, based in Jeddah, Saudi Arabia, through its parent company National Industrialization Company of Saudi Arabia (Tasnee). Cristal is the second largest TiO2 producer in the world and Tasnee is the second largest industrial conglomerate in the Saudi. Tasnee has already invested $4 million in the project.
Dyesol earlier this year forged a two-year research cooperation pact with Nanyang Technological University, in Singapore, for dye solar cell development, following similar agreements on several continents. Apart from the Dyesol/Dyetec efforts, perhaps a dozen other companies are working to develop commercial-scale dye solar cells. The U.S. Department of Energy’s National Renewable Energy Laboratory, in Golden, CO, also has been at work to develop nanotubes and other TiO2 forms for use in solar cells for several years.
In a basic dye solar cell, a TiO2 layer with absorbed dye is used as an anode to collect and transmit electrons excited by its exposure to sunlight. “The particle size of TiO2 anatase is in the range of 10 to 25 nanometers with a film thickness of 5 to 15 micrometers and a porosity of around 60 percent to ensure a large internal surface area for adsorbing dye molecules,” according to Materials Today.