Introduction: Our society use fossil fuels such as coal, oil and natural gas, but these fossil fuels will be depleted someday in the future because they are limited. CO2 is produced in the combustion of fossil fuels and the quick increase of CO2 concentration has affected the consequence of climate, resulting in the global warming effect. Under these circumstances, interest in photovoltaic (PV) solar cell is increasing rapidly as an alternative and clean energy source. Photovoltaic solar cells provide clean electrical energy because the solar energy is directly converted into electrical energy without emitting carbon dioxide. The solar energy is not limited, free of charge and distributed uniformly to all human beings. Crystalline silicon solar cell has been extensively studied and used for practical terrestrial applications. However, the expensive material cost and lots of energy necessary for manufacturing have caused high cost and long energy payback time, which have prevented the large spread of PV power generation. Purpose: The purpose of this study is produced a solar cell that achieves very high power-conversion efficiencies (PCEs) by using hybrid nanostructures. This work also addresses the reduction of fabrication cost of the nano-hybrid cells to make them more economically viable as it is easy to proceed and suitable for large-scale production, and paves the way for the growth of some other promising materials to further improve the cell efficiency. The design of hybrid DSSCs structures used in this research is studied and a charge transfer processes of dye sensitized solar cell based on ZnO/CuO hybrid structures are explained. Scope: Under solar irradiation, the dye molecules adsorbed on the n-type semiconductor film’s surface are excited from the ground state to the excited state, and the electron transferred to the lowest unoccupied molecular orbital (LUMO) of the dye is injected into the conduction band (CB) of the typical n-type semiconductor. The electron is transported through the semiconductor layer and then the external circuit to the counter electrode of the DSSC. The electron at the CB of the semiconductor may undergo recombination with the oxidized dyes and the redox couple mediator and this reduces the power conversion efficiency of the cells therefore this process is unfavorable and should be prevented to collect as much as electron possible to increase the PCE of the cells. Limitation: It is widely believed that the ruthenium dyes N719 are regenerated by iodide with near unity quantum yield following photo-oxidation in dye-sensitized solar cells (DSSCs). However, the incident photon-to-current efficiency (IPCE) of DSSCs using these dyes decreases with increasing forward bias, limiting power conversion efficiency (η) compared to the hypothetical constant-IPCE case. This phenomenon could arise due to incomplete regeneration, but despite the important implications for cell efficiency, it has received little attention. The results strongly suggest that this is the case, even for abnormally high iodide concentrations, where η is reduced by as much as 30% by the effect. Method: In this study, CuO nanorods were coated on top of ZnO nanowire photoelectrode to form a barrier layer by hydrothermal method. The photoanode based 1 dimensional (1D) ZnO was prepared by a hydrothermal method. 0.1 g Zn(NO3)2.4H2O and 40 ml deionized water were prepared in a magnetic stirrer. 2 mL ammonia was added to adjust the pH~10.6 of the solution. The solution was placed into a Teflon-lined stainless steel autoclave. The FTO substrates were immersed in the solution, and the autoclave was then sealed and heated to 175 °C for 12 h. In addition to, for produce hybrid structures, 0.52 g CuCl2.H2O and 50 ml deionized water solution was prepared and adjusted to pH ~ 11 using ammonia solutions. The 1D ZnO were putted into the solution and then heated to 150 °C for 24 h. After the growth step, the substrates were dried under a flow of N2 and were then annealed in a furnace at 350 °C in air for 30 min to form the hybrid structures. Results: The hybrid structures have the potential to decrease the chance of electron-hole recombination. The growth of CuO nanorods on ZnO nanowire can effectively obstruct the injected electron from back-transferring from the conduction band of the ZnO to the electrolyte. Consequently, the recombination of photo-generated electron with oxidized dye molecules or tri-iodide in the electrolyte is decreased. The power conversion efficiency and short-circuit current density (Jsc) of ZnO/CuO hybrid photoanodes were obtained around 6.18% and 14.76 mA cm−2 much higher than (~30%) pure ZnO nanowire. Structural, morphological, chemical and optical characterizations were carried out using X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive Spectroscopy (EDS), Raman spectroscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) spectroscopy tools. Conclusion: Hybrid nano-semiconductors were obtained for application in hybrid-DSSCs with enhanced solar conversion efficiency. CuO low band-gap nano-semiconductors were used as a layer on the top of 1D-ZnO to form a blocking layer. Photocurrent measurements indicated that the light-harvesting efficiency of the obtained ZnO/CuO hybrid film was higher than that of bare ZnO nanostructures. Current density-voltage characterization indicated that the ZnO/CuO hybrid structures exhibited remarkably enhanced power conversion efficiency about 30% higher than that of pure ZnO. Our results show that ZnO/CuO hybrid structures are clearly favorable for DSSC applications owing to their fast electron transport, effective diffusion length, and reduced rate of charge recombination.
Anahtar Kelimeler: Dye-sensitized solar cell, ZnO/CuO, Hybrid nano-semiconductors, Nanowires
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