Marko Berginc

Development of TiO2 pastes modified with Pechini sol–gel method for high efficiency dye-sensitized solar cell

A titanium oxide layer used for a dye-sensitized solar cell (DSSC) has to meet two opponent properties to assure a high efficiency DSSC: good connection between TiO2 grains and a large inner surface area. Three different paste formulations based on commercial nanocrystalline TiO2 powder (Degussa P25) are studied. Results confirm that modification of the TiO2 paste with the Pechini sol–gel method increases the surface area of the TiO2 layer while maintaining good connections between the nanocrystalline grains, consequently the efficiency of the DSSC increases from 1.8% to 5.3%. The structure and morphology of the TiO2 layers are described by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD).

Solution processed silver nanoparticles in dye-sensitized solar cells

A plasmonic effect of silver nanoparticles (Ag NPs) in dye-sensitized solar cells (DSSCs) is studied. The solutions of silver nitrate in isopropanol, ethylene glycol, or in TiO2 sol were examined as possible precursors for Ag NPs formation. The solutions were dipcoated on the top of the porous TiO2 layer. The results of optical measurements confirmed the formation of Ag NPs throughout the porous TiO2 layer after the heat treatment of the layers above 100°C. Heat treatment at 220°C was found to be optimal regarding the formation of the Ag NPs. The porous TiO2 layers with Ag NPs have been evaluated also in DSSC by measuring current-voltage characteristics and the external quantum efficiency of the cells. In addition, the amount of adsorbed dye has been determined to prove the plasmonic effect in the cells. The I-V characterization of the DSSCs revealed an increase of the short circuit current in the presence of Ag NPs although the amount of the attached dye molecules decreased. These results confirm that the performance enhancement is related to the plasmonic effect. However, neither a thin sol-gel TiO2 layer nor poly(4-vinylpyridine) shells provide effective protection for the long term stability of the Ag NPs against the corrosion of I3-/I- based electrolyte.

Plasmonic effect in dye-sensitized solar cells

Improvement of the absorption of the dye-sensitized solar cells (DSSCs) through the plasmonic effect is studied by simulations and experiments. Silver nanoparticles (NPs) having different size, density, embedded in different host materials were optically simulated first. The sputtered NPs were optically characterized to prove the presence of the plasmonic effect and the shift of the resonance frequencies. Finally the NPs were integrated in the DSSCs in a compact TiO2 layer at the TCO-active layer interface. The presence of NPs increased the quantum efficiency (QE) around 350 nm and decreased QE around main absorption peak at 550 nm.

Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are recognized as one of the worlds leading innovation in nanosciences and photovoltaic technology. In contrast to the conventional silicon-based solar cells the demand on purity of materials for DSSC is lower and forecasted manufacturing costs are approximately halved which make the DSSCs attractive alternative. Nowadays the conversion efficiency of DSSCs exceeds 10% which makes it competitive with other thin film solar cells. In this chapter the structure and the fundamental operation of the DSSC are presented. Afterwards the properties and requirements for each individual component used in a DSSC are given. In addition advanced hybrid DSSC systems also are presented. In overall, the emphasis of this chapter is given to the involvement of sol-gel chemistry in the preparation of the individual DSSCs components, primarily of TiO2 layers and electrolytes.