Dye-sensitized solar cells typically capture sunlight via a small molecule (dye), enabling this sunlight to be converted into electrical energy. An advantage of carbon-based dyes is that some of them can efficiently transmit the light they absorb.
However, a disadvantage is that they often absorb only a small range of colors, for example, certain colors in the yellow range. This essentially wastes much of the light (energy) they receive, because the sun emits everything from blue to red light.
Neil Pschirer (BASF Research, Germany), Gerrit Boschloo (Uppsala University, Sweden), and coworkers have worked towards addressing this limitation. They have synthesized a dye molecule that absorbs light from the blue to well within the red range of the color spectrum.
Key experimental improvements.
The scientists investigated perylene dyes for their research. These are carbon-based molecules possessing five fused rings, with electrons delocalized throughout the molecule.
Perylene molecules absorb a wide range of colors, are stable, and are easy to synthesize. However, depending on the method utilized to incorporate them within the solar cell, the color range of light absorbed shifts to a less useful range.
These scientists changed the chemistry of the linkage commonly used for incorporation into the solar cell. This resulted in more efficient charge transfer from the dye to other components of the solar cell.
Testing the solar cell.
The scientists then affixed these dye molecules to their model solar cells. In the case of a solid charge carrier, they found that the light-to-current conversion efficiency was over 50% at light wavelengths of 560 nanometers (the approximate transition between green and yellow).
Most notably, conversion efficiency was still above 30% at 700 nanometers (on the border of red and infrared, i.e. near the end of the visible color range). This contributes to an overall power conversion efficiency of 3.2%.
To the best of the scientists' knowledge, this is the largest efficiency yet reported for solid-state solar cells which do not contain the volatile additive known as tert-butyl pyridine. Volatile additives are undesirable in a solar cell.
This is because all of the light it receives quickly heats up the components of the solar cell to fairly extreme temperatures. You don't want the solar cell components boiling away (destroying it).
Perylene molecules show renewed promise as components of dye-sensitized solar cells, in that they can be rigged to efficiently absorb more light than has been observed previously. They may take the place of rare (expensive) metals that are currently one of the gold standards in this line of research.
for more information:
Cappel, U. B., Karlsson, M. H., Pschirer, N. G., Eickemeyer, F., Schöneboom, J., Erk, P., Boschloo, G., & Hagfeldt, A. (2009). A Broadly Absorbing Perylene Dye for Solid-State Dye-Sensitized Solar Cells The Journal of Physical Chemistry C, 113 (33), 14595-14597 DOI: 10.1021/jp906409q