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Abstract

Titanium dioxide (TiO2) in nanoparticle form has recently gained a lot of attention, in both the scientific and industrial communities. This is due to the fact that it exhibits various interesting chemical and physical characteristics, for example, a high photocatalytic activity and the absorption of incident UV light. Many applications have been developed so far, such as UV absorptive coatings, photocatalytically active coatings and dye-sensitized solar cells (DSSCs), which make it possible to produce electrical energy. In particular, the technology of DSSCs and photocatalytic coatings may be of great importance in the field of photovoltaics, which is one of the fastest growing technologies in the world. So far, the most promising photovoltaic technology has been based on silicon semiconductor modules, whose working action is very dependent on the cleanliness of the module surface, which determines the amount of absorbed incident light. Dust and other impurities may lower the efficiency of the silicon module, making the technology more expensive overall due to the required cleaning and maintenance. This also lengthens the overall time for a return on the investment. The use of coatings which would keep the Si module surface clean for a longer period of time could considerably lower the maintenance costs. On the other hand, the relatively new photovoltaic technology, the DSSCs, are based on cheap materials and technology and are a serious candidate for the implementation of low-cost electrical energy acquisition.
The basis of both technologies, photocatalytic coatings and DSSCs, is TiO2 in nanoparticle form. The TiO2 nanoparticles were developed using raw materials emanating from the established Sulphate process of pigment production in Cinkarna Celje Inc. The starting material was metatitanic acid. Using the principles of sol-gel and gel-sol chemistry we transformed it into anatase (TiO2) nanoparticles in polycrystalline form.
The polycrystalline anatase nanoparticles were used in the photocatalytic coating, which was applied to the surface of glass substrates. Then, the coating was analyzed for its photocatalytic activity and the superhydrophilic effect by the use of contact angle measurements and a quantitative method of terephthalic acid sodium salt degradation using a spectrofluorimeter. The coating was also tested on commercially available silicon modules. One module was coated with the photocatalytic coating and compared regarding its efficiency with an uncoated module. The efficiency measurements showed that initially the efficiency of the coated module is not lowered considerably, while long-term tests that are taking place could prove beneficial in keeping the efficiency higher when compared to the uncoated module.
The DSSC technology was based on using a special type of TiO2 nanoparticles, namely the monocrystalline form. Monocrystalline anatase nanoparticles were synthesized by the hydrothermal method using gel-sol derived polycrystalline anatase nanoparticles as the starting material. Monocrystalline anatase nanoparticles were then used as a raw material in TiO2 paste production based on the Pechini method. The paste was deposited onto the conductive glass substrate and sintered, forming a photo-anode which was used to construct the final DSSC. We have shown that by changing the initial paste composition and monocrystalline TiO2 type, various TiO2 pastes can be formed, effectively influencing the efficiency, which was in our case in the range of 0.5–2.3%.