31 October 2011
Precisely engineered dye compounds take
inexpensive, corrosive-free dye-based photovoltaic devices to record
levels of efficiency.
The push-pull dye C229 is coupled with a cobalt-based electrolyte
to achieve high solar
energy conversion efficiency.
The dye-sensitized solar cell (DSC) is a next-generation photovoltaic technology with the potential to reduce the cost of solar energy production to levels comparable to that of fossil fuel-based electricity generation.
DSCs use a mix of dye molecules and
titanium dioxide (TiO2)
nanoparticles to convert sunlight into electricity, and can be
easily and cheaply fabricated into thin, large-area sheets using
simple screen-printing techniques. Despite the promise of this
technology, however, achieving the high conversion efficiencies
needed to approach commercial viability has meant using
resource-limited materials such as ruthenium.
The high price and restricted
availability of ruthenium has led researchers to pursue alternative
‘push-pull’ dye sensitizers - organic molecules containing
electron-accepting and -donating groups linked together by a
conjugated bridge. Finding a suitable organic dye, however, has been
This modification enhanced the dye’s ability to collect red light from the visible spectrum, allowing it to absorb more solar light overall (see image). Combining this photo-sensitizer with cobalt phenanthroline as an electrolyte to regenerate the dye resulted in a DSC system with an energy conversion efficiency of 9.4% under typical daylight conditions - a new benchmark value for ruthenium-free DSCs and only marginally behind the best ruthenium-based systems.
The use of a cobalt-based electrolyte also addresses another shortcoming of ruthenium-based DSCs:
Measurements and quantum calculations revealed that interactions between the cobalt electrolyte and the C229 dye helped lift the system’s reduction-oxidation potential above its ground state, making the cell more receptive to light across the solar spectrum.