The development of new sensitizers based on indoline dyes, has helped to improve the efficiency of photoelectrochemical solar cells.
Berlin, Feb 29 : The development of new sensitizers based on indoline dyes, has helped to improve the efficiency of photoelectrochemical solar cells.
According to a report in the Angewandte Chemie International Edition, this technology has been developed in collaboration with Satoshi Uchida at the University of Tokyo, Michael Gr„tzel and his research group at the Swiss Federal Institute of Technology in Lausanne.
Photoelectrochemical solar cells, which were developed some years ago by Gr„tzel, are inexpensive, easy to produce, and able to withstand long exposure to light and heat.
These Gr„tzel cells", as they are popularly called, contain a mesoscopic layer of titanium oxide (TiO2) particles coated with a sensitizing dye.
Upon irradiation with light, electrons are injected from the dye adsorbed on the TiO2, which are then transferred to the conducting band of the TiO2 and collected at the back contact, and carried away by an external circuit.
In order for the cell to work, the electrons that are injected into the TiO2 must not recombine with the oxidized dye. To prevent this, the cell contains an electrolyte solution with negatively charged iodide and triiodide ions as a redox couple dissolved in a solvent, which immediately reduce the holes created in the dye.
The main disadvantage of using volatile organic solvent in the electrolyte is the need for encapsulation of the electrolyte. The high viscosity of these electrolytes is detrimental to the mass transport and consequently a problem for obtaining high efficiency.
Gr„tzel and his team compensated for this loss of efficiency by optimizing the sensitizer.
In place of the usual ruthenium dyes, they used tailor-made organic dyes based on indoline, which have a higher molar extinction coefficient. This allows the TiO2 films to be thinner, in turn reducing the electron path length.
The combination thus attained an energy conversion yield of 7.2 %. This is a record for this type of cell.
ANI