Influence of Synthesis-Dependent Structural Morphology on Performance of Natural Dye-Sensitized ZnO Solar Cells (original) (raw)
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This paper reports on the synthesis of ZnO nanowires (NWs), as well asthe compound nanostructures of nanoparticles (NPs) and nanowires (NWs+NPs) with different coating layers of NPs on the top of NWs and their integration in dye-sensitized solar cells (DSSCs). In compound nanostructures, NWs offer direct electrical pathways for fast electron transfer, and the NPs of ZnOdispread and fill the interstices between the NWs of ZnO, offering a huge surface area for enough dye anchoring and promoting light harvesting. A significant photocurrent density of 2.64 mA/cm2 and energy conversion efficiency of 1.43% was obtained with NWs-based DSSCs. The total solar-to-electric energy conversion efficiency of the NWs+a single layer of NPs was found to be 2.28%, with a short-circuit photocurrent density (JSC) of 3.02 mA/cm2, open-circuit voltage (VOC) of 0.74 V, and a fill factor (FF) of 0.76, which is 60% higher than that of NWs cells and over 165% higher than NWs+a triple layer of NPs-based DSSCs....
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.
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ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band gap semiconducting photoelectrode in dye-sensitized solar cells (DSSCs). The nanowires provide a direct path from the point of photogeneration to the conducting substrate and offer alternative semiconductor network morphologies to those possible with sintered nanoparticles. Growing nanowires with dendrite-like branched structure greatly enhances their surface area, leading to improved light harvesting and overall efficiencies. Hybrid cells based on a combination of nanowires and nanoparticles can be tailored to take advantage of both the high surface area provided by the nanoparticles and the improved electron transport along a nanowire network. Solar cells made from branched nanowires showed photocurrents of 1.6 mA/cm 2 , internal quantum efficiencies of 70%, and overall efficiencies of 0.5%. Solar cells made from appropriate hybrid morphologies show photocurrents of 3 mA/cm 2 and overall efficiencies of 1.1%, while both the nanowire and hybrid cells show larger open circuit voltages than nanoparticle cells.
Beilstein Journal of Nanotechnology, 2017
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ZnO nanoparticle-nanowire ͑NP-NW͒ array hybrid photoanodes for dye-sensitized solar cell ͑DSC͒ with NW arrays to serve as a direct pathway for fast electron transport and NPs dispersed between NWs to offer a high specific surface area for sufficient dye adsorption has been fabricated and investigated to improve the power conversion efficiency ͑PCE͒. The overall PCE of the ZnO hybrid photoanode DSC with the N3-sensitized has reached ϳ4.2%, much higher than both ϳ1.58% of ZnO NW DSC and ϳ1.31% of ZnO NP DSC, prepared and tested under otherwise identical conditions.
Effects of Na-doping on the efficiency of ZnO nanorods-based dye sensitized solar cells
Journal of Materials Science: Materials in Electronics, 2014
Na-doped ZnO nanorods (Zn 1-x Na x O: x = 0.0, 0.02, 0.04) were grown by a chemical bath deposition method on ZnO seeded FTO substrates. The influence of Na-doping on the efficiency of ZnO nanorods-based dye-sensitized solar cells (DSSCs) was investigated. Undoped and Na-doped ZnO nanorods were used as photo-anodes for the fabricated DSSCs. X-ray diffraction measurements exhibited that all the samples had a wurtzite structure of ZnO with a preferred orientation of (002) plane. Scanning electron microscopy images of the samples revealed that all the samples displayed hexagonal shaped nanorods. It was observed from optical measurements that the band gap energy gradually decreased from 3.29 to 3.21 eV for undoped and 4 at.% Na-doped ZnO nanorods, respectively. Photoluminescence spectrum for undoped ZnO showed three peaks located at 379, 422, and 585 nm corresponding to UV emission, zinc vacancy, and deep level emission (DLE) peaks, respectively. When ZnO nanorods were doped with 2 at.% Na, the intensity of UV peak increased whereas the intensity of DLE peak decreased. The maximum conversion efficiency of DSSCs was found to be 0.22 % with a J sc of 0.80 mA/cm 2 , V oc of 0.49 V, and fill factor of 0.523 as ZnO nanorods were doped with 2 at.% Na atoms.
Journal of Alloys and Compounds, 2011
ZnO film with a novel bilayer structure, which consists of ZnO nanowire (ZnO NW) arrays as underlayer and polydisperse ZnO nanocrystallite aggregates (ZnO NCAs) as overlayer, is fabricated and studied as dye-sensitized solar-cell (DSSC) photoanode. Results indicate that such a configuration of the ZnO nanocrystallite aggregates on the ZnO nanowire arrays (ZnO-(NCAs/NWs)) can significantly improve the efficiency of the DSSC due to its fast electron transport, relatively high surface area and enhanced lightscattering capability. The short-circuit current density (J sc) and the energy-conversion efficiency (Á) of the DSSC based on the ZnO-(NCAs/NWs) photoanode are estimated and the values are 9.19 mA cm −2 and 3.02%, respectively, which are much better than those of the cells formed only by the ZnO NWs (J sc = 4.02 mA cm −2 , Á = 1.04%) or the ZnO NCAs (J sc = 7.14 mA cm −2 , Á = 2.56%) photoanode. Moreover, the electron transport properties of the DSSC based on the ZnO-(NCAs/NWs) photoanode are also discussed.