Understanding Dye-Loading Mechanism at Interface Advances Next-Generation Solar Cell Study

The Japan Science and Technology Agency (JST) and Kyoto University jointly announced on April 27, 2011, that a research team led by Associate Professor Hideo Ohkita at Kyoto University has demonstrated efficiency improvements of dye-sensitized polymer solar cells, elucidating, for the first time in the world, the principle of selective dye loading at the interface.

A polymer solar cell, a type of organic flexible solar cell, has a film structure with a mixture of polymer and fullerene derivative, and has received much attention as a next generation solar cell, based on its being easy to mass produce at low cost by means of printing process. However, since the light absorption capacity of the polymer is limited only to the visible spectrum, its low conversion efficiency (less than 8 percent) has been a hurdle. In order to improve the conversion rate, researchers have attempted to load a dye sensitive to near-infrared light, which shares approximately 40 percent of sunlight, at the polymer/fullerene interface. The efforts proved, however, that it was difficult to regulate an inner structure during the formation of polymer solar cells by means of solution process.

Following the success in generating dye-sensitized polymer solar cell in 2009, the team this time successfully elucidated the principle of a mechanism in which the light-harvesting dye (a silicon phthalocyanine derivative (SiPc)) is selectively located at the poly (3-hexylthiophene) (RP-P3HT) /fullerene (PCBM) interface. They confirmed that the dye was located at the interface because its surface had medium surface energy between that of P3HT and PCBM. This is similar to the effect of surfactant as represented by soap with intermediate surface energy between water and oil. They then confirmed that crystallization of P3HT enhanced the dye segregation into the interface similar to the effect of freeze-desalination process under which the salt in seawater is expelled when seawater is slowly frozen.

The finding is expected to significantly accelerate the progress of applying dye sensitization to the polymer solar cells.

Light, Flexible Solar Cell Developed (Related JFS article)
http://www.japanfs.org/en/pages/025421.html

Posted: 2011/08/13 06:00:15 AM