Urša Opara Krašovec

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.

Three-state regulator for electrochromic windows

Abstract Electrochromic (EC) windows enable to change their optical transmittance by applying appropriate electrical signals to the window structure. In many applications, such as “smart” EC buildings’ windows is required, an automatic control of the windows transmittance, in order to assure a constant level of transmitted daylight for different outdoors’ illuminations. For this purpose we develop an analogue three-state electronic regulator which controls an “all sol–gel” EC device intensity of transmitted light on a constant pre-selected level. In this paper, first of all, the structure and the performances of an all sol–gel EC window is given. Then the electrical schematic of the regulator is represented and explained in detail. The performances of the regulator are demonstrated by electrical and optical measurements. At the end a demonstrational application—EC sun-glasses with an accompanying handy regulator—is presented.

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.

Laminated Electrochromic Glazing with Optically Passive Counter-Electrodes and Organic-Inorganic Ionic Conductors

Publisher Summary The future energy saving requirements placed on modem buildings require that windows have to meet higher standards, including being able to reduce heat-loss while avoiding overheating of the building and gaining solar energy while assuring comfortable daylighting. These conflicting demands can be satisfied by using switchable or “smart” windows, the optical properties (transmittance and reflectance) of which can be varied between low and high transmitting states. This could be done either manually or automatically by the buildings own energy management system. Sol-gel processing together with the dip-coating deposition technique is gaining importance in the field of film manufacturing, since it allows the preparation of layers with controlled stoichiometry, structure, and texture. This chapter provides an overview of counter-electrode films prepared in laboratory together with their properties, which are photopic transmittance and charge capacity. Photopic transmittances of model electrochromic (EC) devices composed of counter-electrodes and an active EC WO3 layer were calculated to gain information about the possible optical modulation of the devices. Examples of the spectral characteristics of experimentally composed EC devices are shown and the materials science aspects of certain deposited films are discussed.

Spatial characterization techniques for dye-sensitized solar cells

Spatial characterization techniques are applied to dye-sensitized solar cells (DSSCs). A comparison between transmittance imaging (TI), light-beam-induced-current (LBIC) scan and electroluminescence imaging is carried out. Detected types of inhomogeneities have different fingerprints by each applied technique. Electroluminescence (EL) is advantageous over TI because the electrical activity of the inhomogeneities influences the result. EL is also advantageous over the LBIC scan due to shorter acquisition time. Based on the above findings, EL has been used for characterization of DSSCs during outdoor short-term aging, showing that EL imaging is a proper method to follow the evolution of the inhomogeneities. Proof-of-concept EL inspection of a screen-printed dyesensitized solar module shows good uniformity.

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.