Unravelling the Chemical Morphology of a Mesoporous Titanium Dioxide Interface by Confocal Raman Microscopy: New Clues for Improving the Efficiency of Dye Solar Cells and Photocatalysts

The presence of anatase and rutile domains on nanocrystalline films of P25 TiO(2), as well as the distinct coordination modes of carboxylates on those phases, were revealed by confocal Raman microscopy, a technique that showed to be suitable for imaging the chemical morphology down to submicrometric size.

Layer-by-layer TiO(2) films as efficient blocking layers in dye-sensitized solar cells

Charge recombination at the conductor substrate/electrolyte interface has been prevented by using efficient blocking layers of TiO(2) compact films in dye-sensitized solar cell photoanodes. Compact blocking layers have been deposited before the mesoporous TiO(2) film by the layer-by-layer technique using titania nanoparticles as cations and sodium sulfonated polystyrene, PSS, as a polyanion. The TiO(2)/PSS blocking layer in a DSC prevents the physical contact of FTO and the electrolyte and leads to a 28% increase in the cell`s overall conversion efficiency, from 5.7% to 7.3%. (C) 2009 Elsevier B.V. All rights reserved.

Efficient and low cost devices for solar energy conversion: Efficiency and stability of some natural-dye-sensitized solar cells

Dye-sensitized solar cells, named by us Dye-Cells, are one of the most promising devices for solar energy conversion due to their reduced production cost and low environmental impact, especially those sensitized by natural dyes. The efficiency and stability of devices based on natural sensitizers such as mulberry (Morus alba Lam), blueberry (Vaccinium myrtillus Lam), and jaboticaba`s skin (Mirtus cauliflora Mart) were investigated. Dye-Cells prepared with aqueous mulberry extract presented the highest P(max) value (1.6 mW cm(-2)) with J(sc) = 6.14 mA cm(-2) and V(oc) = 0.49 V, Photoelectrochemical parameters of 16 cm(2) active area devices sensitized by mulberry dye were constant for 14 weeks of continuous evaluation. Moreover, the cell remained stable even after 36 weeks with a fairly good efficiency. Therefore, mulberry dye opens up a perspective of commercial feasibility for inexpensive and environmentally friendly Dye-Cells. (C) 2009 Elsevier B.V. All rights reserved.

Buried screen-printed contacts for silicon solar cells

A Simple way to improve solar cell efficiency is to enhance the absorption of light and reduce the shading losses. One of the main objectives for the photovoltaic roadmap is the reduction of metalized area on the front side of solar cell by fin lines. Industrial solar cell production uses screen-printing of metal pastes with a limit in line width of 70-80 μm. This paper will show a combination of the technique of laser grooved buried contact (LGBC) and Screen-printing is able to improve in fine lines and higher aspect ratio. Laser grooving is a technique to bury the contact into the surface of silicon wafer. Metallization is normally done with electroless or electrolytic plating method, which a high cost. To decrease the relative cost, more complex manufacturing process was needed, therefore in this project the standard process of buried contact solar cells has been optimized in order to gain a laser grooved buried contact solar cell concept with less processing steps. The laser scribing process is set at the first step on raw mono-crystalline silicon wafer. And then the texturing etch; phosphorus diffusion and SiNx passivation process was needed once. While simultaneously optimizing the laser scribing process did to get better results on screen-printing process with fewer difficulties to fill the laser groove. This project has been done to make the whole production of buried contact solar cell with fewer steps and could present a cost effective opportunity to solar cell industries.

Impedance Spectroscopy Analysis of the Effect of TiO2 Blocking Layers on the Efficiency of Dye Sensitized Solar Cells

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Doping saturation in dye-sensitized solar cells based on ZnO:Ga nanostructured photoanodes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electron Transport in Dye-Sensitized Solar Cells Based on ZnO Nanotubes: Evidence for Highly Efficient Charge Collection and Exceptionally Rapid Dynamics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Synthesis and characterization of mesoporous TiO2 nanostructured films prepared by a modified sol-gel method for application in dye solar cells

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and characterization of ZnO and ZnO : Ga films and their application in dye-sensitized solar cells

Highly crystalline ZnO and Ga-modified zinc oxide (ZnO:Ga) nanoparticles containing 1, 3 and 5 atom% of Ga3+ were prepared by precipitation method at low temperature. The films were characterized by XRD, BET, XPS and SEM. No evidence of zinc gallate formation (ZnGa2O4), even in the samples containing 5 atom% of gallium, was detected by XRD. XPS data revealed that Ga is present into the ZnO matrix as Ga3+, according to the characteristic binding energies. The particle size decreased as the gallium level was increased as observed by SEM, which might be related to a faster hydrolysis reaction rate. The smaller particle size provided films with higher porosity and surface area, enabling a higher dye loading. When these films were applied to dye-sensitized solar cells (DSSCs) as photoelectrodes, the device based on ZnO: Ga 5 atom% presented an overall conversion efficiency of 6% (at 10 mW cm(-2)), a three-fold increase compared to the ZnO-based DSSCs under the same conditions. To our knowledge, this is one of the highest efficiencies reported so far for ZnO-based DSSCs. Transient absorption (TAS) study of the photoinduced dynamics of dye-sensitized ZnO:Ga films showed that the higher the gallium content, the higher the amount of dye cation formed, while no significant change on the recombination dynamics was observed. The study indicates that Ga-modification of nanocrystalline ZnO leads to an improvement of photocurrent and overall efficiency in the corresponding device.

Efficient Dye-Sensitized Solar Cells Based on the Combination of ZnO Nanorods and Microflowers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ga-Modified Nanostructured ZnO: Characterization and Application in Dye-Sensitized Solar Cells

ZnO has received great attention in many applications due to its electronic and optical properties. We report on the preparation of ZnO and gallium-containing ZnO (ZnO:Ga) nanoparticles by the precipitation method. The nanoparticles have the wurtzite structure and a high crystallinity. Gallium ions are present as Ga(3+), as evidenced by the binding energies through XPS. Porosity and surface area of the powder increased under increasing gallium level, explained by the smaller particle size of ZnO:Ga samples compared with ZnO. The estimated optical band gap of ZnO was 3.2 eV, comparable to ZnO:Ga.

Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells based on ZnO and ZnO:Ga

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Impedance spectroscopy study of solid-state dye-sensitized solar cells with varying Spiro-OMeTAD concentration

This work reports on the changes of performance of solid-state cells dye-sensitized solar cells with the variation of concentration of spiro-OMeTAD between 5% and 25% in the fabrication of the cell. Variations of charge recombination and capacitance correlate with the improvement of current-potential characteristics at increasing spiro-OMeTAD content, which is explained by reduction of transport resistance for hole transport, the increase of charge separation in the dye molecules, and importantly, with the increase of the β-factor in the recombination resistance, that causes a reduction of the diode ideality factor. © 2010 Materials Research Society.

Optical spectrum of bottom-up graphene nanoribbons: towards efficient atom-thick excitonic solar cells

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)