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Abstract: A phenomenological model is proposed for a better understanding of the basic working mechanisms of dye-sensitized solar cells (DSCs). A steady-state approach allows the construction of the I–V characteristics, giving important informations about the main factors that influence DSCs’ performance. On the other hand, the transient approach model is an important tool to relate the phenomenological behavior with certain dynamic techniques, such as Electrochemical Impedance Spectroscopy (EIS). Bearing in mind the uncertainty arising from fitting the experimental Nyquist diagrams to general electrical analogues, this transient model contributes for a deeper understanding of the DSCs and for obtaining the relevant kinetic parameters with higher accuracy. The one-dimensional transient phenomenological model presented here assumes that the injected conduction-band electrons may recombine only with the electrolyte redox species. Due to the small dimension of the titania particles, no significant electrical potential gradient is considered, resulting only in a diffusive electron transport across the semiconductor. For modeling purposes, the mesoscopic porous structure, consisting of TiO2 nanoparticles covered with light-absorbing dye molecules and interpenetrated by the redox mediator (electrolyte), is considered as a homogeneous nanocrystalline structure of thickness L. The continuity and transport governing equations are defined for the mobile species involved: electrons in the TiO2 conduction band and ions in the electrolyte. The simulated results are in straight agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: The photocurrent-voltage characteristic of a photoelectrochemical cell for solar hydrogen production via water splitting, using undoped-hematite as photoanode, was obtained. Photoelectrochemical characteristics of the cell were also investigated by electrochemical impedance spectroscopy. Both techniques were carried out in the dark and under illumination. The analysis of the frequency spectra for the real and imaginary parts of the complex impedance allowed obtaining equivalent electrical analogs for the PEC cell operating in the dark and under 1 sun simulated illumination. Additionally, different electrode configurations were used (two and three-electrode arrangements). The two-electrode configuration allowed the study of the overall charge transfer phenomena occurring at the semiconductor, within the electrolyte and at the counter-electrode side of the cell, whereas the three-electrode configuration gave more detailed information concerning the double charged layer at the semiconductor/electrolyte interface. [ABSTRACT FROM AUTHOR]

Highly ordered anodic hafnium oxide (AHO) nanoporous or nanotubes were synthesized by electrochemical anodization of Hf foils. The growth of self-ordered AHO was investigated by optimizing a key electrochemical anodization parameter, the solvent-based electrolyte using: Ethylene glycol, dimethyl sulfoxide, formamide and N-methylformamide organic solvents. The electrolyte solvent is here shown to highly affect the morphological properties of the AHO, namely the self-ordering, growth rate and length. As a result, AHO nanoporous and nanotubes arrays were obtained, as well as other different shapes and morphologies, such as nanoneedles, nanoflakes and nanowires-agglomerations. The intrinsic chemical-physical properties of the electrolyte solvents (solvent type, dielectric constant and viscosity) are at the base of the properties that mainly affect the AHO morphology shape, growth rate, final thickness and porosity, for the same anodization voltage and time. We found that the interplay between the dielectric and viscosity constants of the solvent electrolyte is able to tailor the anodic oxide growth from continuous-to-nanoporous-to-nanotubes. [ABSTRACT FROM AUTHOR]

Solar energy harvesting and chromogenic technologies can be integrated together to give self-powered and wireless photoelectrochromic devices (PECD). Due to the similarity in the architecture of both dye-sensitized solar cells (DSC) and electrochromic devices (ECD), it is possible to merge these two devices into one combined solar-powered electrochromic device known as DSC-EC. The present work describes the preparation and characterization of electrochromic solar cells using PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) as electrochromic material in the counter-electrode. Different configurations and liquid and polymer-based electrolytes are studied. The resulting electrochromic solar cells were characterized focusing on the determination of solar to electricity conversion efficiency and the color contrast was assessed using color coordinates under simulated solar irradiation. The best DSC-EC configuration originates a color contrast of ( Δ E = 30) at a potential difference of 0.4 V and energy conversion efficiency of 4.9% at V OC of 0.66 V and J SC of 11 mA cm −2 , when using the liquid electrolyte. On the other hand, the best performing DSC-EC using the polymer-based electrolyte showed a very good color contrast of (ΔE = 47) at short circuit and an energy conversion efficiency of 1% at V OC of 0.63 V and J SC of 4.5 mA cm −2 . [ABSTRACT FROM AUTHOR]

In an industrial context, the re-utilization of resources is very important to monetize processes, reducing the production costs without overlooking a proper performance of the devices. For specific applications such as dye-sensitized solar cells (DSC), a high-aspect-ratio configuration of the produced TiO 2 nanotubes (NTs) is essential to achieve higher conversion efficiencies. In this work, we report the effect of electrolyte re-utilization in the diameter, length and morphology of TiO 2 nanotubes (NTs) produced by electrochemical anodization. A detailed study of the bias voltage effect on the anodic NTs for new and re-utilized electrolytes was performed. Also, the possibility of obtaining NT arrays with ribs morphology just by re-using the electrolyte was unveiled. [ABSTRACT FROM AUTHOR]