Rapid deposition of titania nanoparticles on tin oxide for dye solar cell anodes using fluid mechanics and eletrokinetics

Using electrokinetics and fluid mechanics, we are designing a method to rapidly deposit titania nanoparticles onto transparent conductive oxide surfaces for use in dye solar cell anodes. Manipulating the pH and ionic strength of an aqueous solution makes it possible to control the surface potential of submerged oxide surfaces such as titania and tin oxide. By using pH values near and below 5.5, it is possible to create conditions where titania nanoparticles are stable and electrostatically repel each other in a dilute, aqueous suspension, but are attracted to various tin oxide surfaces. We can then use fluid flow such as that from a rotating disk or impinging jet to deliver nanoparticles adequately close to the surface such that they adhere via strong van der waals forces. For particles which are made in solution via oxidation, this technique offers the major advantage of never drying the particles, thus allowing them to remain un-aggregated until they deposit onto the surface. We have shown that we can monitor particle deposition in situ by measuring the zeta potential of a surface using a rotating disk electrode apparatus. The measured difference in iso-electric point of titania and both fluorine- and indium-tin oxide shown in this work indicates that we should have some control over the rate and extent of particle deposition. Currently, we have deposited titania nanoparticle layers which are several layers thick and consist of particles with diameters smaller than 10 nm; these tightly packed layers have applications as blocking layers to prevent unwanted shunts in dye solar cells.