Researchers at the Center for Solar and Thermal Energy Conversion (CSTEC) have explored molecular organic dye design tools for photocurrent generation efficiency in dye-sensitized solar cells (DSSCs) and developed a novel organic dye that exhibits excellent efficiencies and photocurrents.
The need for environmentally sustainable and renewable energy technologies relies on natural resources such as sun and wind. Solar cells directly convert energy from the sun to electricity. In recent years, DSSCs have emerged as a low-cost and environmentally friendly alternative to conventional silicon-based solar cells. Organic dyes make DSSCs sensitive to sunlight and produce power by means of a porous semiconductor film. Upon light absorption, the organic dye molecule goes to its excited state and subsequently injects electrons into the film. The leftover holes are transported to another electrode through electrolytes. The circulation of electrons into DSSCs results in the production of electricity. Thus, solar energy is converted to electrical energy and stored.
To improve the performance of DSSCs, previous studies have examined adding an electron donor/acceptor system, technically called a D-π-A structure, into the organic dye framework. However, compared to similar structures without electron-withdrawing acceptor groups, they don't convert as much sunlight to energy. The CETEC researchers developed a reliable dye-design tool and synthesized a novel organic dye with higher efficiency for DSSCs.
The reliable dye-design tool clarifies how organic dyes are more efficient. Specifically, the researchers discovered the relationship between metal-free organic dyes' exciton binding energy and its photocurrent efficiency by using reliable computational tools and complex calculations. An exciton, an electron/hole pair, transports energy. Researchers inserted a designed molecular structure into the organic dyes; they hold excitons loosely, resulting in a more efficient light-to-electricity conversion for better performing DSSCs. The researchers revealed that the exciton binding energy is inversely related to the maximum efficiency of the dyes. With their well-established dye-design principles, the researchers developed a novel organic dye, termed EB-01. It showed an excellent light-to-electricity conversion efficiency and outstanding power conversion efficiency.
"Achieving power conversion efficiency over 9 percent from a metal-free organic dye through the computational/experimental hybrid type of approach was very exciting. Now, we have better understanding on rational dye design for excitonic solar cells," remarks Jinsang Kim, associate professor at University of Michigan, who led the team of researchers at CSTEC.
With this information, scientists can optimize dyes through molecular design to increase efficiency of the light-to-electricity conversion. This new tool and research provides a new path to develop novel organic dyes with better performance for DSSCs.
