TiO2 Films For Dye-sensitized Solar Cells Research Articles

Hierarchically macro–mesoporous TiO2 film via self-assembled strategy for enhanced efficiency of dye sensitized solar cells

The hierarchically porous structure of TiO2 film plays an important role on improved photoelectric conversion efficiency in dye-sensitized solar cells (DSSCs). It is highly required to develop a facile strategy to prepare the hierarchical porous photoelectrode. In this study, a novel hierarchically macro–mesoporous TiO2 film as photoelectrode of DSSCs is fabricated by a self-assembled process of TiO2 nanoparticles via TiF4 hydrolysis. The hydrolysis of TiF4 is accompanied with self-assembled process of TiO2 nanoparticles on the surface of electrophoretic-deposited titanate nanotube film which provides effective active sites for the deposition of TiO2 nanoparticles owing to a large amount of hydroxyl groups, resulting in the formation of hierarchically porous structures. The hierarchically porous TiO2 film is mainly composed of mesopores with a size of 2–50nm and macropores with a wide range of 0.5–5μm, which contribute to an obviously higher conversion performance (6.70%) than nonporous P25-TiO2 film (4.01%). The main reasons for enhanced conversion efficiency of hierarchically porous TiO2 film can be attributed to adsorption of more dye molecules, rapid diffusion and efficient transport of electrolyte, and longer electron lifetime. This work may provide new insights into preparing porous structure of TiO2 films in DSSCs for modification of photoelectric conversion efficiency.

Characterization of nano-crystalline structure of TiO2for Dye-sensitized Solar Cells by Raman spectroscopy and spectroscopic ellipsometry

ABSTRACTDye-sensitized solar cells (DSSCs) are attractive alternatives to conventional solid-state photovoltaic devices because of performance, stability, environmental compatibility and cost. In contrast to the conventional systems where the semiconductor assumes both the task of light absorption and charge carrier transport, these two functions are separate in DSSC and, therefore, efficiency is very sensitive to the cell structure/composition. High-efficiency DSCs based on mesoporous nanocrystalline titanium dioxide (TiO2) electrodes have received considerable research attention in the past decade. Grain size and thickness of the mesoporous TiO2film have shown a dominant effect on the efficiency of the photovoltaic devices.We have investigated screen printed TiO2films deposited on a textured fluorinated SnO2(FTO) glass substrate, using Raman spectroscopy and spectroscopic ellipsometry. Materials were prepared by repeating a same screen-printing procedure once, twice and three times, using TiO2paste with 10nm, 20 nm and 200nm particles sequentially. Raman spectra of PV devices cells taken at different excitation (266 nm, 325 nm, 364 nm, 532 nm, 633 nm, and 1064 nm) as well as pure TiO2oxides are presented. Different excitation wavelengths allow to probe different depth of the sample. It was found that there is strong correlation of the position and the width of E2gmode of anatase at 144 cm-1and size of TiO2particles. The samples show that this peak shifts to the high frequency region and becomes broader for small size particles. The position and broadening of the peak can be described by optical confinement model that depends on the size of nano-crystals. Results showed varying grain sizes as correlated with different TiO2paste applied. Thickness, optical constants and porosity of TiO2films were determined by spectroscopic ellipsometry. In this work, we have demonstrated the use of Raman Spectroscopy and Spectroscopic Ellipsometry for non-destructive characterization of nanocrystalline TiO2films for dye-sensitized solar cells.

Effect of binder molecular weight on morphology of TiO2 films prepared by tape casting and their photovoltaic performance

Titanium(IV) oxide in the form of anatase has proven to be the best choice for photoanodic material in dye-sensitized solar cells (DSCs). The aim of the work was to study the influence of binder molecular weight on the morphology of deposited films, and consequently, DSC parameters. For this study, five different TiO2 tape casting slips were prepared from commercially available nanoanatase powder and polyethylene glycol (PEG) as a binder. The process of drying and sintering was carefully designed, so that the organic template was slowly decomposed, leaving favorable crack-free, porous structure. It was found that there is an optimal region of binder molecular weight for obtaining homogeneous, nonagglomerated and porous microstructure which is a necessary condition for application of TiO2 films in DSCs.

The Influence of Titania Electrode Modification with Lanthanide Ions Containing Thin Layer on the Performance of Dye-Sensitized Solar Cells

The lanthanide and scandium groups ions (except Pm and Ac) have been used as dopants of TiO2film in dye-sensitized solar cells. The X-ray diffraction spectra show that the modification has no influence on the structure of the electrode; however, the diffuse reflectance UV-Vis measurements exhibit significant changes in the electronic properties of modified electrodes. The appearance of energy barrier preventing photoexcited electron back-transfer was confirmed for Sc, Ce, Sm, Tb, Ho, Tm, and Lu modified cells. The best photoconversion performance of 8.88 and 8.80% was found for samples modified with Ce and Yb, respectively, and it was greater by 31.4 and 30.2% than that of a unmodified cell.