Oct 26, 2010
SWCNT films outperform platinum in dye-sensitized solar cells
Dye-sensitized solar cells (DSCs) are a strong candidate for next-generation solar cells offering high photovoltaic efficiency and low fabrication cost. One important step in the light-to-electricity conversion process is the regeneration of the redox species at the counter electrode. The counter electrode is required to be conductive and catalytic. Traditionally, platinum (Pt) is used due to its high conductivity and excellent catalysis, but the material has problems of high cost and can degrade in the electrolytes of DSCs. Various materials have been investigated to replace Pt and among them, carbon nanotubes (CNTs) are quite promising. In this case, the most effective way to process CNTs onto conductive substrates is by coating. However, a binder-like polymer is usually needed to improve the adhesion. Unfortunately, the binder can lower the catalysis and the conductivity of CNT films.
To overcome the problem, a research group at the National University of Singapore has recently developed a gel-coating method for preparing CNT films on various substrates. The CNT gels, also called bucky gels, are formed by dispersing CNTs in a liquid nonionic surfactant, such as polyoxyethylene(12) tridecyl ether or low-molecular weight polyethylene glycol, via mechanical grinding or ultrasonication. The gels can be coated onto substrates using a surgical blade. The nonionic surfactant, which disperses the CNTs, can be removed by heating at a temperature below the decomposition temperature of CNTs. As a result, the gel-coated CNT films are free of binder. The CNT films have good adhesion to substrates and do not detach from the substrates when in water or organic electrolytes over a long period.
As shown in the study, the binder-free CNT films fabricated by gel coating provide excellent electrochemical catalysis and can effectively catalyse the redox of iodide and triiodide. Devices featuring a gel-coated binder-free single-walled CNT (SWCNT) or multi-walled CNT (MWCNT) film as the counter electrode exhibit a photovoltaic efficiency comparable with the control DSCs based on a conventional Pt counter electrode. Moreover, the DSCs with the SWCNT counter electrode have better stability than the control DSCs.
The researchers presented their work in the journal Nanotechnology.
About the author
Xiaoguang Mei and Swee Jen Cho are currently PhD candidates under Prof. Ouyang's supervision at the National University of Singapore. Mei's research focuses on developing novel approaches to disperse CNTs and graphenes and exploring new applications of these materials. Cho has been making efforts to develop energy materials for energy devices, including DSCs and fuel cells. Benhu Fan is a research engineer and he has been working on developing high-performance third-generation solar cells, including DSCs and organic photovoltaic cells. Dr Ouyang is currently an assistant professor at the Department of Materials Science and Engineering, National University of Singapore. His lab develops high-performance organic and nanomaterials and devices.