Abstract
Photoelectrodes for dye-sensitized solar cells were fabricated using commercially available zinc oxide (ZnO) nanoparticles and sensitized with the dye N719. This study systematically investigates the effects of two fabrication factors: the ZnO film thickness and the dye adsorption time. Results show that these two fabrication factors must be optimized simultaneously to obtain efficient ZnO/N719-based cells. Different film thicknesses require different dye adsorption times for optimal cell performance. This is because a prolonged dye adsorption time leads to a significant deterioration in cell performance. This is contrary to what is normally observed for titanium dioxide-based cells. The highest overall power conversion efficiency obtained in this study was 5.61%, which was achieved by 26-μm-thick photoelectrodes sensitized in a dye solution for 2 h. In addition, the best-performing cell demonstrated remarkable at-rest stability despite the use of a liquid electrolyte. Approximately 70% of the initial efficiency remained after more than 1 year of room-temperature storage in the dark. To better understand how dye adsorption time affects electron transport properties, this study also investigated cells based on 26-μm-thick films using electrochemical impedance spectroscopy (EIS). The EIS results show good agreement with the measured device performance parameters.
Highlights
Dye-sensitized solar cells (DSSCs) are regarded as promising low-cost solar cells with high light-toenergy conversion efficiency
These two samples exhibited similar patterns except for differences in the peak intensity. Apart from those corresponding to the fluorine-doped tin oxide (FTO) substrate, the diffraction peaks can be indexed to the hexagonal wurtzite zinc oxide (ZnO) (JCPDS card no. 79–0206)
No other diffraction peaks were found in both cases, indicating that the prepared ZnO films are of the pure wurtzite phase, and no phase transformation occurs during thermal treatment
Summary
Dye-sensitized solar cells (DSSCs) are regarded as promising low-cost solar cells with high light-toenergy conversion efficiency. The basic principle of the light scattering method is to confine light propagation and extend the traveling distance of light within the oxide film In this way, the opportunity of photon absorption by the dye molecules is increased, so is the cell conversion efficiency. In traditional DSSCs, the porous photoelectrode typically consists of nanocrystallites of approximately 20 nm in diameter to ensure a large interfacial surface area; to generate light scattering, submicron-sized particles are incorporated into the nanocrystalline film. A promising three-dimensional nanostructure that has been developed to fulfill multiple functions in DSSCs is nanocrystallite aggregates [26,27,28,29] These aggregates provide a large interfacial surface area, and generate light scattering because they are composed of nanoparticles that assemble into submicron aggregates. Mixing the large particles into the nanocrystalline film unavoidably causes a decrease in the interfacial surface area of the film, whereas placing the large particles on top of the nanocrystalline film brings about a limited increase in the interfacial surface area of the film
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