Due to their high photoelectric conversion potential, DSSCs are a promising source of renewable energy. One critical aspect limiting higher conversion efficiency is recombination of the photoinjected electrons with the oxidised redox species. One strategy currently under investigation to decrease recombination losses is the treatment of the titania film with various types of insulating layers. One approach that we are using involves the attachment of various organic groups on the titania surface following porphyrin dye adsorption/attachment. These organic molecules on "free" titania sites have the potential to prevent contact between the triiodide and the surface, thereby reducing charge recombinations. In addition, they may also change the conduction band energy of the semiconductor and electron injection into the semiconductor.
In the project, the effect of treating the titania surface with various organic carboxylic, phosphonic or sulfonic acids on the performance of DSSCs is being examined. Treated titania films were analysed using IR spectroscopy to confirm chemical attachment and to develop correlations between treatment times and surface concentrations of the organic acid. The results of testing of DSSCs constructed using these treated films showed definitive trends with the agent used. For example, phosphonic acid treatment resulted in poorer performing cells than those that underwent sulfonic acid treatment.