• Energy Research

We report on the synthesis of two new dyes to be employed as sensitizers in p-type dye-sensitized solar cells (DSCs). The design of the two new molecules under consideration has been inspired by the state-of-art dye PMI-6 T-TPA. In particular, a specific engineering of the thiophene-based central core is here considered to favour structural planarity between an oligothiophenic π-spacer (a sexithiophene), and the acceptor and donor units made by peryleneimide (PMI) and triphenylamine (TPA) moieties, respectively. This leads to a wide absorption in the NIR with stabilization of the HOMO energy level in the resulting dyes, as supported by TD-DFT simulations and spectroscopic characterization. When tested as sensitizers in NiOx-based p-type DSCs, A6D (with an Acceptor-π-Donor structure) outperforms both its counterpart with a Donor-π-Donor structure (D6D) and P1, a benchmark dye in the field of p-DSCs. With A6D dye-sensitizer the resulting DSC device presents the quite remarkable value of stabilized efficiency as high as 0.15 % when I-/I3- is employed as redox couple and nanostructured NiOx photocathode is thick less than 2 μm and does not contain any blocking layer. Notwithstanding the panchromatic feature of the sensitizer, A6D-based devices show an average visible transmittance (AVT) of 8 %. Such a result paves the way toward the application of these types of multifunctional dyes in semi-transparent solar cells.

The chemical dissolution of anodically grown Si oxides in acidic fluoride medium has been studied in-situ with the Bending Beam Method (BBM). Current and deflection transients were recorded after switching the electrode from the given polarization conditions to zero applied field and monitoring the etchback process. Oxide stress values estimated with this approach are free from contributions due to film electrostriction and to changes in surface tension. Transients recorded after polarization in the regime of current or potential oscillations show dissolution patterns which contain information on the properties of oxide film along its depth profile.

Undyed mesoporous NiO in the configuration of thin film (thickness 2–3 μm) presents photoelectrochemical activity as cathode of a p-type dye-sensitized solar cell (p-DSC) towards the reduction of triiodide to iodide under irradiation with a solar simulator. The photoelectroactivity of the oxide prepared via microwave plasma sintering (or rapid discharge sintering, RDS) has been observed in the spectral range 300–500 nm with the incident photon-to-current conversion efficiency (IPCE) reaching a maximum of 8.7 % at 375 nm. Upon sensitization, the characteristic photoelectrochemical activity of NiO can be either enhanced or depressed depending on the nature of the dye-sensitizer. The comparative analysis of the JV and IPCE curves of the p-DSCs based on bare NiO and four differently sensitized NiO cathodes reveals that N719, black dye (BD), and commercial squaraine 2 (SQ2) decrease the efficiency of conversion of dyed NiO with respect to bare NiO in the range of photoelectroactivity of the latter (300–500 nm). The fourth dye P1 represents the sole exception since its employment brings about an enhancement of the quantum efficiency of P1-sensitized vs. unsensitized NiO up to a maximum of 21 % within the spectral interval of reference for NiO (300–500 nm). Outside the range of NiO photoelectrochemical activity, i.e., λ > 500 nm, only N719 does not introduce a gain of quantum efficiency with respect to bare NiO despite the observation of spectral sensitization up to 580 nm for N719-sensitized NiO. The impedance spectra recorded under illumination shows a direct proportionality between the overall efficiency (η) of the variously sensitized p-DSCs and the amplitude of the semicircle which is generally associated with the process of charge recombination at the electrode/electrolyte interface with η decreasing with the increase of the recombination resistance.

Tandem dye-sensitized solar cell shows higher photoconversion performances with respect to parent devices with single photoactive electrode thanks to careful photocurrent matching and complementarity of electrodes optical absorption.

Spray deposition followed by sintering of nickel oxide (NiO x ) nanoparticles (average diameter: 40 nm) has been chosen as method of deposition of mesoporous NiO x coatings onto indium tin oxide (ITO) substrates. This procedure allows the scalable preparation of NiO x samples with large surface area (~103 times the geometrical area) and its potential for applications such as electrocatalysis or electrochemical solar energy conversion, which require high electroactivity in confined systems. The potential of these NiO x films as semiconducting cathodes for dye-sensitized solar cell (DSC) purposes has been evaluated for 0.3–3-μm-thick films of NiO x sensitized with erythrosine B (ERY). The electrochemical processes involving the NiO x coatings in the pristine and sensitized states were examined and indicated surface confinement as demonstrated by the linear dependence of the current densities with the scan rate of the cyclic voltammetry. Cathodic polarization of NiO x on ITO can also lead to the irreversible reduction of the underlying ITO substrate because of the mesoporous nature of the sintered NiO x film that allows the shunting of ITO to the electrolyte. ITO-based reduction processes alter irreversibly the properties of charge transfer through the ITO/NiOx interface and limit the range of potential to NiO x coatings sintered for DSC purposes.

Abstract The application of four pyran based dyes as sensitizers for p-type dye-sensitized solar cells (p-DSCs) is here proposed. The dyes differ for the nature of the electron acceptor group which functionalizes the pyran core. Such a structural variation significantly influences the optical properties of the dyes so that the new pyrans overall cover most of the visible spectrum. In some cases, the p-DSCs employing these pyran-based dyes display power conversion efficiency significantly higher than the device sensitized with sensitizer benchmark P1. The relevant photo-electrochemical activity of one of the reported dyes combined with its ability to absorb the visible radiation in the lower energy portion (λ > 500 nm) makes it a promising candidate to be used in a tandem DSC (t-DSC) with the photoanode sensitized by a dye typically absorbing the higher energy zone of the visible spectrum (λ

The mechanical effects of the intercalation processes in electrochromic WO 3 thin films are reported here and discussed. In particular the electrochemical insertion of H, Li and Na ions in WO 3 was studied by means of laser beam deflection method (LBDM). Linear changes of WO 3 stress were observed for small amounts of the inserted charge and linearity was always associated with a reversible mechanical behavior of thin films. An explanation in terms of homogeneity of the insertion is given. An analogous trend was also verified in the absorbance vs. charge curves. As a consequence the constancy of the electrochromic efficiency values for the three different ions was found. In this way it was possible to determine a full reversible behavior for M x WO 3 in the composition range 0 ≤ x ≤ 0.2. The onset of new phases formation when x exceeded previous upper limit, was observed during Li and Na intercalation. Such transitions brought about the loss of optical and mechanical reversibility. During prolonged hydrogen insertion a reversible slope inversion occurred in stress curve so that it was necessary to take into account different possible mechanisms of the WO 3 electrochromic reaction.