New type of solar cell retains high efficiency for long periods

Frederic Sauvage, Michael Graetzel and colleagues describe research that aimed to develop an improved version of a highly promising solar cell that is less expensive than conventional solar cells made from the semi-conductor material, silicon. These so-called dye-sensitized solar cells (DSCs), or Graetzel cells (named for the discoverer, Michael Graetzel), have other advantages. They can be manufactured in light-weight flexible sheets, for instance, that are more durable and suitable for roll-up applications such as window shades. Hindering commercial use of DSCs has been their lack of stability, with the electricity output tending to decline over time.

The new study reports development and successful lab tests of a new electrolyte composition suitable for the DSC, constructed with different material that is both stable and has a relatively high efficiency of 10 percent. It has an improved electrolyte system, the substance that conducted electricity inside the solar cell. The new device retained at least 95 percent of that sun-converting ability for 1,000 hours of testing.

More information: Butyronitrile-Based Electrolyte for Dye-Sensitized Solar Cells, J. Am. Chem. Soc., 2011, 133 (33), pp 13103–13109. DOI: 10.1021/ja203480w

Abstract
We elaborated a new electrolyte composition, based on butyronitrile solvent, that exhibits low volatility for use in dye-sensitized solar cells. The strong point of this new class of electrolyte is that it combines high efficiency and excellent stability properties, while having all the physical characteristics needed to pass the IEC 61646 stability test protocol. In this work, we also reveal a successful approach to control, in a sub-Nernstian way, the energetics of the distribution of the trap states without harming cell stability by means of incorporating NaI in the electrolyte, which shows good compatibility with butyronitrile. These excellent features, in conjunction with the recently developed thiophene-based C106 sensitizer, have enabled us to achieve a champion cell exhibiting 10.0% and even 10.2% power conversion efficiency (PCE) under 100 and 51.2 mW·cm–2 incident solar radiation intensity, respectively. We reached >95% retention of PCE while displaying as high as 9.1% PCE after 1000 h of 100 mW·cm–2 light-soaking exposure at 60 °C.

Provided by American Chemical Society