Nanoporous ZnO Photoelectrode for Dye-Sensitized Solar Cell (original) (raw)
Related papers
Self-assembled ultra small ZnO nanocrystals for dye-sensitized solar cell application
Journal of Solid State Chemistry, 2014
We demonstrate a facile chemical approach to produce self-assembled ultra-small mesoporous zinc oxide nanocrystals using sodium salicylate (SS) as a template under hydrothermal conditions. These ZnO nanomaterials have been successfully fabricated as a photoanode for the dye-sensitized solar cell (DSSC) in the presence of N719 dye and iodine-triiodide electrolyte. The structural features, crystallinity, purity, mesophase and morphology of the nanostructure ZnO are investigated by several characterization tools. N 2 sorption analysis revealed high surface areas (203 m 2 g À 1) and narrow pore size distributions (5.1-5.4 nm) for different samples. The mesoporous structure and strong photoluminescence facilitates the high dye loading at the mesoscopic void spaces and light harvesting in DSSC. By utilizing this ultra-small ZnO photoelectrode with film thickness of about 7 μm in the DSSC with an open-circuit voltage (V OC) of 0.74 V, short-circuit current density (J SC) of 3.83 mA cm À 2 and an overall power conversion efficiency of 1.12% has been achieved.
Nanoscale research letters, 2014
Mesoporous ZnO nanoparticles have been synthesized with tremendous increase in specific surface area of up to 578 m 2 /g which was 5.54 m 2 /g in previous reports (J. Phys. Chem. C 113:14676-14680, 2009). Different mesoporous ZnO nanoparticles with average pore sizes ranging from 7.22 to 13.43 nm and specific surface area ranging from 50.41 to 578 m 2 /g were prepared through the sol-gel method via a simple evaporation-induced self-assembly process. The hydrolysis rate of zinc acetate was varied using different concentrations of sodium hydroxide. Morphology, crystallinity, porosity, and J-V characteristics of the materials have been studied using transmission electron microscopy (TEM), X-ray diffraction (XRD), BET nitrogen adsorption/desorption, and Keithley instruments.
ZnO Nanostructures for Dye-Sensitized Solar Cells
Advanced Materials, 2009
This Review focuses on recent developments in the use of ZnO nanostructures for dye-sensitized solar cell (DSC) applications. It is shown that carefully designed and fabricated nanostructured ZnO films are advantageous for use as a DSC photoelectrode as they offer larger surface areas than bulk film material, direct electron pathways, or effective light-scattering centers, and, when combined with TiO 2 , produce a core-shell structure that reduces the combination rate. The limitations of ZnO-based DSCs are also discussed and several possible methods are proposed so as to expand the knowledge of ZnO to TiO 2 , motivating further improvement in the power-conversion efficiency of DSCs.
Hierarchically Assembled ZnO Nanocrystallites for High-Efficiency Dye-Sensitized Solar Cells
Angewandte Chemie International Edition, 2011
Photoelectrochemical cells are promising devices for cheap, environmentally compatible, and large-scale solar energy conversion as an alternative to conventional solid-state semiconductor solar cells. Among excitonic cells, dyesensitized cells (DSCs) exhibit the highest performance in terms of energy conversion efficiency and long term stability, despite the fact that the efficiency remains below 13 % because of the intrinsic limitation in charge transport. The structure of the photoelectrodes is crucial in determining the functional properties of the photoelectrochemical system. In particular, the photoanode consists of a mesoporous wideband-gap oxide semiconductor film with a high specific surface (typically a thousand times larger than the bulk counterpart). To date, the highest photoconversion efficiency (PCE) has been achieved with film consisting of 20 nm TiO 2 nanocrystallites sensitized by different dye molecules (11.1 % for N719 dye, over 10 % for "black dye", and 11.4 % for C101, ). In addition to TiO 2 , a series of other ntype metal oxide semiconductors can in principle be used in DSCs, such as ZnO, SnO 2 , and In 2 O 3 . Much attention has been recently devoted to ZnO owing to its higher electron mobility and similar electronic band structure with respect to TiO 2 . Various strategies have been addressed to enhance PCE in ZnO-based DSCs, which are mainly based on tailoring the geometrical and structural features of ZnO. A possible solution to reduce electron recombination could be the use of one-dimensional nanostructures that are able to provide a direct pathway for the rapid collection of photogenerated electrons. However, only low PCE has been achieved to date, mainly because of the reduced internal surface area of the nanostructures. Hybrid structures have also been tested to improve light collection, such as combination of nanoparticles and nanowires (maximum PCE = 4.2 %), or hierarchical nanowires (maximum PCE = 2.63 %). Another strategy to enhance PCE is application of hierarchical photoanodes composed of large aggregates of nanocrystallites, which can act as light scattering centers while maintaining a high specific surface area. The synthetic procedure of photoanode preparation is crucial to improve PCE: an optimized photoanode composed of just ZnO nanoparticles without any geometrical feature for light confinement or enhanced electron transport resulted in the highest value of PCE (6.58 %) for a ZnO-based DSC. Herein we present the fabrication and characterization of hierarchically structured ZnO-based photoanodes in DSCs to enhance the PCE. Our approach addresses specifically the following points: 1) High optical density of the sensitized layer, allowing complete light absorption in the spectral range of the dye; 2) high light scattering of the absorbing layer, enhancing the time spent by light inside the sensitized film and improving light absorption; and 3) inhibition of back electron transfer between the conducting layer at the anode and the electrolyte. The films are prepared by the simple, cheap, and large-area-scalable spray pyrolysis method. The films are composed of polydispersed ZnO aggregates consisting of nanosized crystallites while submicrometer-sized aggregates act as efficient light scattering centers and nanoparticles provide the mesoporous structure and the large specific surface area needed for high dye loading. Additionally, a ZnO compact layer is intentionally formed between the conducting substrate and the layer composed of polydispersed aggregates. Such a layer acts as an efficient blocking layer for electron back reaction between the conducting glass at the anode and the electrolyte, improving the functional properties of the cells. This is the main innovation with respect to the work of Cao and co-workers, leading to unprecedented PCE up to 7.5 %, which is larger than ZnO nanoparticles (6.58 %), hierarchically structured ZnO without a blocking layer (5.4 %), and hierarchically arranged ZnO nanowires (2.63 %). As a further benefit, our method is extremely fast (no more than 1.5 h for the complete processing of a photoanode, while typically 8 h or 10 to 14 h are required), enabling its technological implementation.
Influence of morphology on the performance of ZnO-based dye-sensitized solar cells
ZnO nanomaterials with different morphologies, obtained by a sonochemical synthesis method at pH values of 5.5, 8, 10 and 12, have been used as starting materials for the fabrication of dye-sensitized solar cells. The morphology of the nanomaterials and the texture of the films deposited using screen printing depend on the synthesis pH, and the various exposed surface facets interact in a different manner with the dye and electrolyte solutions. The best cell performance was obtained with the morphology that resulted from the synthesis at pH 10, where the {100} and {110} crystal forms are predominant, and where dye coverage was largest. Interestingly, the BET total surface area was lowest for this nanomaterial illustrating the importance of morphology. The influence of the synthesis pH was also evident in the energetics and recombination kinetics of the solar cells. For the ZnO material synthesized at pH 5.5, the band edges appear to be shifted to more negative potentials, which could have resulted in a larger open circuit potential based on thermodynamic considerations. However, the electron life time for the pH 5.5 ZnO material is significantly smaller than for the other three synthesis pH values, indicating that the recombination kinetics are significantly faster for these cells as well, resulting in a smaller open circuit potential based on kinetics arguments. The balance between these two effects determines the experimentally observed open circuit potential. Overall, the results indicate that the dependence of the dye adsorption characteristics on ZnO nanomaterial morphology and film texture are the dominating factors that determine the solar cell performance.
Physica Status Solidi B-basic Solid State Physics, 2013
Stacked ZnO structures made of a nanoporous film superimposed on a dense underlayer have been prepared by electrochemical deposition on fluoride doped SnO 2 substrates. The growth conditions of the two components have been optimized in order to get efficient photoelectrodes after sensitization by the D149 metal-free indoline dye. From the dye-sensitized solar cell characteristics, the optimal underlayer and nanoporous layer deposition times have been determined. Moreover, the porosity induced by the use of an organic structure directing agent, eosin Y, has been found optimum for a concentration of 50 mM.
Sponge-like Porous ZnO Photoanodes for Highly Efficient dye-sensitized Solar Cells
Acta Physica Polonica A, 2013
We propose a 3D branched ZnO nanostructure for the fabrication of highly ecient dye-sensitized solar cell photoanodes. A coral-shaped structured Zn layer was deposited by radio frequency magnetron sputtering at room temperature onto uorine-doped tin oxide/glass sheets and then thermally oxidized in ambient atmosphere, obtaining a high-density branched ZnO lm. The porous structure provides a large surface area, and, as a consequence, a high number of adsorption sites, and the size and spacing of the nanostructures (on the order of the exciton diusion length) are optimal for good electron collection eciency. The proposed synthesis technique is simple and scalable and the reproducibility of the growth results was tested. The crystalline phase of the lm was investigated, evidencing the complete oxidation and the formation of a pure wurtzite crystalline structure. ZnO-based solar harvesters were fabricated in a microuidic architecture, using conventional sensitizer and electrolyte. The dependence of the cell eciency on dye incubation time and lm thickness was studied with IV electrical characterization and electrochemical impedance spectroscopy. The obtained conversion eciency values, with a maximum value of 4.83%, conrm the highly promising properties of this material for the implementation in dye-sensitized solar cell photoanodes.
Electrochimica Acta, 2011
Dye-sensitized solar cells (DSCs) with films (photoelectrodes) of ZnO nanopowders and nanorods were constructed and investigated. Films having different thicknesses were fabricated by an electrophoretic deposition technique (EPD) and sensitized using different concentrations of a N719 dye solution. Adsorption isotherms for this dye were obtained and showed different behaviors depending upon whether the adsorbent was nanopowders or nanorods. The DSCs were characterized by linear sweep voltammetry and electrochemical impedance spectroscopy. The photo-electrochemical performance of these DSCs was measured and cell performance depended on the thickness of films, concentration of dye solution used, and the film structure. The DSC having an electrodeposited film of ZnO nanorods showed a higher efficiency than that containing ZnO nanopowders.
Study of Porous Nanoflake ZnO for Dye-Sensitized Solar Cell Application
American Journal of Engineering and Applied Sciences, 2009
Problem statement: Nano-scale porous ZnO with high surface area have been studied to enhance physicochemical and electrochemical properties of certain optoelectronic devices applications. Approach: ZnO porous structure consists of flake-shape particles was synthesized through pyrolitic reaction of hydrozincite as Chemical Bath Deposition (CBD) product. Flake-like particle perpendicularly lied on substrate was obtained after 24 hours deposition. After calcinations, cavities on particle surface were observed as additional pores. Result: Sample crystallinity and morphology before and after calcinations were characterized by XRD, FTIR and SEM. Porosity profile was evaluated to its particle structure using N 2 adsorption-desorption. Surface area was calculated using BET and it was 15 m 2 gram −1 . Conclusion: The particle growth in CBD technique had been observed through its morphology and crystalline structure. Macropores structure was formed by cavities among the nanoflakes lied random on substrate and give surface area of 15.1866 m 2 gram −1 .