Ana F. Nogueira

New insights into dye-sensitized solar cells with polymer electrolytes

Polymer electrolytes or gel polymer electrolytes are interesting alternatives to substitute liquid electrolytes in dye-sensitized solar cells (DSSC). The interest in this research field is growing continuously, reflected in the increase in the number of papers published each year concerning these materials. This feature article presents a brief review of the history and development of polymer electrolytes aiming at applications in DSSC. Recent improvements achieved by modifications of the composition and by introduction of additives such as inorganic nanofillers, organic molecules and ionic liquids are described. The stabilities of DSSC assembled with these materials are also discussed and further improvements that can be introduced to maximize performance of the solar cell, such as photoelectrode modification, will also be presented.

Transient optical studies of charge recombination dynamics in a polymer/fullerene composite at room temperature

The recombination kinetics of photogenerated charge carriers in a composite of poly[2-methoxy-5- (3′,7′-dimethyloctyloxy)-1-4-phenylene vinylene], (MDMO–PPV) and the functionalised fullerene 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 are investigated at room temperature by transient absorption spectroscopy. The decay dynamics of positively charged MDMO–PPV polarons were found to be either monophasic or biphasic, depending upon the laser excitation density employed. The slower, power law, decay phase (100 ns–10 ms) is attributed to recombination dynamics of localized polarons, while the fast decay component (<20 ns) is attributed to recombination of relatively mobile polarons observed when the density of localized states is exceeded by the density of photogenerated polarons (∼1017 cm−3). The implications of these observations are discussed in relation to polymer/C60 photovoltaic cells.

Electrochemical and Structural Characterization of Polymer Gel Electrolytes Based on a PEO Copolymer and an Imidazolium-Based Ionic Liquid for Dye-Sensitized Solar Cells

Polymer electrolytes based on mixtures of poly(ethylene oxide-co-propylene oxide) and 1-methyl-3-propyl-imidazolium iodide (MPII) were investigated, aiming at their application in dye-sensitized solar cells (DSSC). The interactions between the copolymer and the ionic liquid were analyzed by infrared spectroscopy and (1)H NMR. The results show interactions between the ether oxygen in the polymer and the hydrogen in the imidazolium cations. The ionic conductivities, electrochemical behaviors, and thermal properties of the electrolytes containing different concentrations of MPII were investigated. The electrolyte containing 70 wt % MPII presented the highest ionic conductivity (2.4 x 10(-3) S cm(-1)) and a diffusion coefficient of 1.9 x 10(-7) cm(2) s(-1). The influence of LiI addition to the electrolytes containing different concentrations of MPII was also investigated. The DSSC assembled with the electrolyte containing 70 wt % MPII showed an efficiency of 3.84% at 100 mW cm(-2). The stability of the devices for a period of 30 days was also evaluated using sealed cells. The devices assembled with the electrolyte containing less ionic liquid showed to be more stable.

The effects of CdSe incorporation into bulk heterojunction solar cells

Hybrid solar cells based on CdSe nanoparticles and a PPV-type polymer containing fluorene and thiophene units (PFT) were investigated. The CdSe/PFT devices showed very low photocurrent and fill factor values, which was attributed to the poor charge transport in the TOPO-capped CdSe nanoparticle phase. Thus, ternary systems based on mixtures of PFT/CdSe and the fullerene derivative PCBM were investigated. The CdSe:PCBM ratio was varied, and nanoparticles with different sizes were also used. It was observed that for the optimized composition of 20 wt% PFT + 40 wt% CdSe + 40 wt% PCBM the devices presented higher photocurrents and efficiencies. The photophysical and electrochemical properties and microscopy images (AFM and HRTEM) of the ternary systems were systematically investigated to elucidate the mechanism of action of the inorganic nanoparticles in these ternary hybrid devices.

Enhancement of photocurrent generation and open circuit voltage in dye-sensitized solar cells using Li+ trapping species in the gel electrolyte

The influence of the addition of 12-crown-4 ether in a gel polymer electrolyte based to a PEO copolymer and its application in dye sensitized solar cells were investigated. Introduction of these Li+ trapping species brought beneficial contributions to both V(oc) and J(sc) values, increasing the devices performance.

Flexible photoelectrochemical devices based on conducting polymers

In this work, we have investigated the photoelectrochemical behavior of conjugated polymers in flexible solid-state devices exploring some unique features that they exhibit: the possibility of adjusting the band gap energy by employing different structures and improving the light harvesting by the addition of an organic dye. We also report the use of these materials as photoactive materials and counter-electrodes in optical devices, depending on their oxidized or reduced state. The overall conversion efficiency is higher than for other photoelectrochemical devices, which exploit the photoconductivity and photosensitivity of organic materials, and the performance remains constant when the devices are bent; however, it is low in comparison to solid-state devices using inorganic materials.

Poly(ethylene oxide-co-epichlorohydrin)/NaI: a promising polymer electrolyte for photoelectrochemical cells

We have investigated the thermal and ionic conductivity properties of the elastomer poly(ethylene oxide-co-epichlorohydrin) filled with NaI and I2. The reason for using this composition is its potential application as electrolyte in photoelectrochemical cells. This copolymer was characterized as a function of NaI concentration, temperature and relative humidity. According to the data obtained, the Na+ ion interacts with the ethylene oxide repeating units by means of Lewis type acid–base interactions. The empirical Vogel–Tamman–Fulcher equation was used to model the conductivity and temperature relationships, indicating that the conduction occurs in the amorphous phase of the copolymer. The sample with 9.0% (w/w) of NaI presents a conductivity of 1.5×10−5 S cm−1 in a dry atmosphere (30°C, [H2O]<1 ppm) and 2.0×10−4 S cm−1 at 86% relative humidity (22°C).

A facile nonaqueous route for fabricating titania nanorods and their viability in quasi-solid-state dye-sensitized solar cells

A facile and simple process has been detailed for the synthesis of titanium glycerolate nanofibers using glycerol as both a solvent and a chelating agent. This complex has then been successfully converted to a high surface area anatase phase of titanium dioxide (TiO2) through solid state transformation without alteration in the overall fiber morphology. The structure, crystallinity and morphology of the products before and after transformation have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), solid-state 13C NMR and thermogravimetric analysis (TGA) measurements. As a demonstration of a potential application, these anatase nanorods (NRs) have been used as a photoanode to fabricate a dye-sensitized solar cell (DSSC) using a gel polymer electrolyte. Devices with efficiencies of 2.8% and 4.4% were recorded under light intensity of 100 mW/cm2 and 10 mW/cm2 illumination respectively.

Solid-state photoelectrochemical device using poly(o-methoxy aniline) as sensitizer and an ionic conductive elastomer as electrolyte

Abstract We report on a photoelectrochemical cell based on polymers (electrolyte and sensitizer) and TiO 2 . Poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I 2 was used as electrolyte and poly( o -methoxy aniline) doped with p -toluenesulfonic (PoAni-TSA) as dye. The short-circuit current and open-circuit voltage obtained with illumination at 120 mW cm −2 are 12.2 μA cm −2 and 0.048 V, respectively, indicating that the ionic conductive elastomer is appropriated for assembling a totally solid device. The monochromatic photon-to-current conversion efficiency decreases from 1.3% to 0.1%, from 410 to 600 nm, respectively, showing that the conducting polymer acts as a dye for TiO 2 , injecting electrons into its conduction band.

Synthesis and characterization of a quaternary nanocomposite based on TiO2/CdS/rGO/Pt and its application in the photoreduction of CO2 to methane under visible light

‘Together we are stronger’ In this work, the preparation of the quaternary nanocomposite TiO2/CdS/rGO/Pt is reported along with its application, for the first time, as a catalyst for the photocatalytic reduction of carbon dioxide (CO2) to methane (CH4). TiO2/CdS nanoparticles and Pt nanoparticle-decorated reduced graphene oxide sheets (rGO/Pt) were synthesized separately and characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, UV-vis spectroscopy and photoelectrochemical experiments. Hydrocarbon samples were collected and analysed using gas chromatography (GC). After 5 hours of illumination under visible light, 0.11 μmol of CH4 was produced at an average production rate of 0.0867 μmol h−1, which is higher than the production of CH4 measured from the TiO2/CdS and the TiO2/CdS/Pt control samples. The photoelectrochemical experiments confirmed that the presence of rGO sheets in the nanocomposite enhanced the electrochemical and photocatalytic properties of the nanocomposite as a result of rapid electron transport and the inhibition of charge recombination.