Flavio S. Freitas

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.

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.

Synthesis of C60-containing Polymers by Ring-opening Metathesis Co-polymerization of a C60-cyclopentadiene Cycloadduct and N-(cycloheptyl)-endo-norbornene-5,6-dicarboximide and their Application in a Photovoltaic Device

A C60-cyclopentadiene cycloadduct and N-(cycloheptyl)-endo-norbornene-5,6-dicarboximide were utilized as co-monomers in ring-opening metathesis polymerization (ROMP) reactions to afford a series of polymers containing C60 in varying ratios. The polymerization reactions were catalyzed by the Grubbs second-generation ruthenium catalyst, and the co-polymers formed were investigated by spectroscopic and thermal techniques. The photovoltaic behavior of the new materials was studied by the construction of a simple sandwich-type photovoltaic cell. Under irradiation we concluded that the C60 in the copolymers simultaneously accelerated both the charge separation in the polymer and the charge recombination between the electrons in the TiO2 and the electrolyte.

Incorporation of nanocrystals with different dimensionalities in hybrid TiO2/P3HT solar cells

Abstract. We investigate the effect of TiO2 nanoparticles–nanospheres and nanorods–inserted in the poly(3-hexylthiophene) (P3HT) matrix of TiO2/P3HT inverted hybrid solar cells. X-ray diffraction, high-resolution transmission electron microscopy, small-angle x-ray scattering, photoluminescence, and photoelectrochemical experiments were employed to investigate the structure, morphology, and photoactivity of TiO2 nanoparticles modified with 2-thiopheneacetic acid, mixed or not with P3HT. Both TiO2 nanospheres and TiO2 nanorods presented a good dispersion in the polymer matrix. The incorporation of TiO2 nanospheres and nanorods has improved the photocurrent generation, and devices with efficiency values up to 1.35% were obtained. Our results reveal that the nanoscale morphology enables an enhanced interfacial area for exciton dissociation. In particular, the nanospheres contribute with their high specific area, and the nanorods contribute with their high aspect ratio.

Polymer electrolytes for dye-sensitized solar cells

Abstract: Polymer electrolytes or gel-type polymer electrolytes are interesting alternatives to substitute liquid electrolytes in dye-sensitized solar cells (DSSC). The interest in this research field is growing, reflected in the increased number of papers published each year concerning these materials. This chapter presents a brief review of the history and development of polymer electrolytes aiming at the application 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 stability of DSSC assembled with these materials, and scaling-up of such devices are also discussed.

Organic and Hybrid Solar Cells Based on Small Molecules

In this chapter, the recent literature involving small molecule-based organic solar cells (OSCs) will be reviewed. The number of papers published in the fields of organic semiconductor and OSCs has grown exponentially in the past decade. Such growth is stimulated by the exciting properties of these materials, combined with the possibility to produce colored, flexible, transparent and cheap solar cells. The main focus of this review is to give an overview and a perspective of the recent advances in this area, highlighting the most interesting results, novel materials as well as their limitations and challenges. This chapter will explore the properties and applications of several classes of small organic molecules, as electron donors and acceptors, dyes, and hole transport materials. Different architectures and techniques will be also discussed in the assembly of double, heterojunction, and multilayer films.