Silicon solar cells use an electric field to push the negatively charged electrons and positive charges apart. While chloroplasts adopt a more subtle approach of separate charges by making a distinction between the units that generate the electron and those that transport it away.
Deciding to copy nature’s trick, Michael Gratzel and Brian O’Regan at the Swiss Federal Institute of Technology began research and produced the Grätzel cell in 1991.
The Grätzel cell uses intensely colored organic dye molecules to capture light energy to inject an electron from the dye into a semiconductor such as titanium dioxide (TiO2). This remarkably efficient charge separation reaction initiates current flow and the output of electrical energy by the cell.
How does nanoscience help?
The ideal material used in the cell must have a high surface area for light absorption and charge separation. Nanoparticles, having a comparable surface area to volume ratio, provides for just that. Titanium dioxide nanoparticles are used to make nanoporous thin film supported upon a glass substrate. The material obtained has optical transparency, excellent stability and good electrical conductivity.
The benefit of these novel photoelectrical solar cells is that they can be fabricated from cheap, low purity materials by simple and low cost procedures. Contrary to expectation, some of the new devices also have strikingly high conversion efficiency. The size-tunable bandgaps of the semiconductor nanoparticles, due to size quantisation, also means more efficient solar cells can be produced for photovoltaics (electricity production) and water splitting (hydrogen production) processes.