Dye-Sensitized Solar Cells Set New Efficiency Benchmark with Low-Volatility and Solvent-Free Electrolyte

29 October 2008

Researchers in China and Switzerland are reporting efficiencies as high as 10% from new practical dye-sensitized solar cells (DSCs, or Grätzel cells) with low volatility and solvent-free electrolyte. In addition to the higher efficiencies, the new cells also showed greater stability at high temperatures than previous formulas, retaining more than 90% of their initial output after 1,000 hours in full sunlight at 60°C. Their study is scheduled for the 13 November issue of ACS’ The Journal of Physical Chemistry C.

The research, conducted by Dr. Peng Wang of the Chinese Academy of Sciences and colleagues—including Dr. Michaël Grätzel, inventor of the first dye-sensitized solar cell—involves photovoltaic cells composed of titanium dioxide and a new type of ruthenium-based dye that helps boost the light-harvesting ability.

DSCs are less expensive than standard silicon-based solar cells and can be made into flexible sheets or coatings. Although promising, DSCs have had serious drawbacks, including low conversion efficiencies, a drop in performance after relatively short exposures to sunlight, and the use of toxic and volatile solvents, which require expensive hermetic sealing.

Using a volatile electrolyte, DSC technology has delivered efficiency of up to 11.0-11.3% measured under the standard air mass 1.5 global (AM 1.5G) sunlight—about half that of the best silicon solar cell. [AM 1.5G is the intensity of insolation equivalent to the sun shining through the atmosphere to sea level, with oxygen and nitrogen absorption, at an oblique angle 48.2 degrees from the vertical (zenith).] Despite the lower efficiencies, the DSCs offer stable output over a moderate temperature range as well a response to weak and diffuse light.

In the past several years, much work has been focused on the development of practical DSCs by using low-volatility electrolytes, solvent-free ionic liquids, or solid organic hole-transporters. Promoted by material designing together with device engineering, the highest efficiency of a stable device with a low-volatility electrolyte now stands at 9.1%, whereas that of its counterpart with a solvent-free electrolyte is 7.7%.Shi et al. (2008)

Using a nanocrystalline titania film stained with the new ruthenium sensitizer, the researchers achieved 9.6-10.0% and 8.5-9.1% efficiencies in conjunction with low-volatility and solvent-free electrolytes under AM 1.5G solar illumination.

The research team is working on stability studies of a testing cell at 80° C and long-term evaluations of a large solar panel with the newly developed systems.

Resources

• Dong Shi, Nuttapol Pootrakulchote, Renzhi Li, Jin Guo, Yuan Wang, Shaik M. Zakeeruddin, Michaël Grätzel, and Peng Wang (2008) New Efficiency Records for Stable Dye-Sensitized Solar Cells with Low-Volatility and Ionic Liquid Electrolytes ASAP J. Phys. Chem. C, doi: 10.1021/jp808018h

• Yu Bai, Yiming Cao, Jing Zhang, Mingkui Wang, Renzhi Li, Peng Wang, Shaik M. Zakeeruddin and Michaël Grätzel (2008) High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts. Nature Materials 7, 626 - 630 doi: 10.1038/nmat2224