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Ultrafast Spectroscopies for Dye Sensitised Solar Cell study and Optimisation

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Ultrafast imaging of solar cell function

Harvesting solar energy has become one of the main goals of the international community in an effort to decrease dependence on fossil fuels while investing in renewable resources. EU-funded researchers developed technologies to enable characterisation of the next generation of solar cells.

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Most photovoltaic (PV) devices, those that generate voltage and current from solar energy, are based on electron flow and separation related to the p-n junctions of the semiconductors in the devices. Dye-sensitised solar cells (DSSCs), on the other hand, are based on electron flow in a system consisting of a photosensitised (covered with a molecular dye that absorbs sunlight) titanium oxide (TiO2) anode, a liquid electrolyte and a platinum cathode. While DSSCs offer a technically feasible, cost-effective alternative to conventional PV devices, clear understanding of their functioning is still lacking and increased efficiency is desirable. Ultrafast (on the order of femtoseconds, or quadrillionths of a second) spectroscopies provide the technology to study the photo-electrochemistry of DSSCs. European researchers initiated the ‘Ultrafast spectroscopies for dye sensitised solar cell study and optimisation’ (ULTRADSSC) project to conduct the first electro-optical characterisation of DSSCs. Scientists evaluated various techniques for deposition of TiO2 given their fundamental role in charge transport mechanisms. Atomic force microscopy was used to evaluate structural and surface properties of the TiO2 films. In addition, numerous materials other than costly platinum were tested to optimise function of the anode. Investigators then evaluated electro-optical characteristics of a prototype device using a sun simulator. In particular, the photocurrent produced by laser illumination was found to increase with the incidence angle of the light, demonstrating up to 25 % enhancements that could be useful to novel device designs. Finally, ULTRADSSC partners set up the ultra-fast resolved spectroscopy laboratory including a femtosecond laser source, an imaging spectrometre and a cooled CCD (charge-coupled device) camera. The experimental materials work combined with the ultrafast spectroscopy setup position the ULTRADSSC team to study electron transfer from dye molecules on the surface of a solid functioning as an electrode. Enhanced understanding of the DSSC mechanisms should lead to more efficient, cost-effective DSSCs with important implications for the international solar energy market.

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