Rapid, continuous in situ monitoring of dye sensitisation in dye-sensitized solar cells

Abstract

Two alternative techniques to the traditional dye desorption method are presented which enable rapid, continuous in situ measurement of dye uptake in porous TiO2 films used in dye-sensitized solar cells (DSC). Measurement of dye uptake is crucial for the rapid up-scaling of DSC technology since currently this is a rate limiting process step typically taking hours to achieve. Most reported measurements of dye sorption have involved desorbing dye at set intervals using a base (e.g.NaOH) followed by UV-vis spectroscopy. Whilst this method is accurate and quantitative, it is time-consuming, destructive of the devices and in situ measurements are impossible. The latter are important as dyeing speeds increase. Here we present two methods to measure the temporal evolution of colour at the interface of porous TiO2 films with TCO-coated glass. The first method uses digital image capture and subsequent image analysis to extract RGB (red-green-blue) colour data enabling a rapid quantification of dye uptake over periods from seconds to hours. The second method uses UV-visible reflectance spectroscopy providing more highly resolved wavelength data; important as DSC co-sensitisation is becoming increasingly important. There is a clear correlation between the two in situ methods reported here as well as with traditional dye desorption methods for measurements made over a period of hours. These methods represent important new tools for the development of ultra-fast dye sensitisation for DSC.