Preparation And Performance Optimization Of Zinc Oxide Based All-solid-state Dye-sensitized Solar Cell

As one kind of the third generation solar cells,dye sensitized solar cell(DSSC) has a lot of advantages such as simple preparation process,simple devices,low cost of materials and so on,so many scholars are attracted by the DSSC and it is an important research field of the solar cells.Compared to liquid-state dye-sensitized solar cell,all-solid-state dye-sensitized solar cell has many advantages such as long service life,high stability,easy package and so on.Ti O2 and Zn O are widely used as the photoanode nanomaterials of DSSC.The band structure of Zn O is similar to Ti O2,but Zn O has a higher carrier mobility,which can shorten time of electron to arrive the external circuit and thus improving the electronic transmission efficiency of DSSC.Zn O nanorods have many advantages,such as high specific surface area, good transmission of electrons,low recombination efficiency of the electron and hole and so on.Therefore,Zn O was used as the photoanode material in order to improve the photoelectric conversion efficiency of DSSC in this paper.In this thesis,hexagonal phase wurtzite structure Zn O nanorods are synthesized by low temperature hydrothermal method.The Zn O nanorods are sensitized by dye Z907 and then mixed with P3 HT to prepare the heterojunction solar cell.The morphology,structure,optical absorption properties and charge transfer efficiency of Zn O nanorods are characterized by field emission scanning electron microscope,X ray diffraction,ultraviolet spectrophotometer, fluorescence spectrometer and I-V curve test instrument.And hexagonal phase zincite structure Zn O nanorod arrays are synthesized by polymer soft template method.The morphology, structure and optical absorption properties of Zn O nanorod arrays are characterized by field emission scanning electron microscope,X ray diffraction,ultraviolet spectrophotometer,fluorescence spectrometer, external quantum efficiency tester and I-V curve test instrument.Conversion efficiency of 0.21%,fill factors of 0.55,open circuit voltage of0.48 V,short circuit current of 0.80 m A/cm2 are obtained when the test effective area of solar cell is 0.16cm2.2.Zn O nanorod arrays are synthesized by polymer soft template method,with C4H10O6 Zn as zinc source, [C6H9NO]n as surfactant.The influence of p H value,Znions concentration,the molar ratio of PVP to zinc acetate and reaction time on the morphology of Zn O are studied and the growth mechanism of Zn O nanorod arrays is also analyzed.(1) The different morphologies of Zn O are synthesized by adjusting the p H value of complex solution.The FESEM result shows that the polar growth trends of Zn O nanostructures are more and more obvious when the p H value increases from p H1 to p H2.The XRD result shows that all samples are hexagonal phase zincite structure and the intensity of(002) diffraction peak enhances obviously.The UV-vis spectra result shows that the absorption edge increases from 391 nm to 421 nm and the PL spectra result shows the crystallinity of Zn O becomes better.(2) Different length and diameter of Zn O nanorod arrays are synthesized by adjusting the Zn ions concentration.The FESEM results show that the morphology of Zn O is rivet which grows on the dense layer of Zn O when the Zn ions concentration is M1.The average length of Zn O nanorods increases from 0.26μm to 1μm and the average diameter of Zn O nanorods increases from 33 nm to 95 nm when the Zn ions concentration increases from M2 to M5.The XRD spectra result shows that the intensity of(002) diffraction peak increases obviously.The UV-vis spectra result shows that the absorption edge increases from 400 nm to 420 nm and the PL spectra result shows the crystallinity of Zn O becomes better.(3)Different length and diameter of Zn O nanorod arrays are synthesized by adjusting the molar ratio of PVP to zinc acetate. FESEM result shows that the average diameter of Zn O nanorods is about 70nm-80 nm and the average length of Zn O nanorods decreases from1.18μm to 0.76μm, respectively and the XRD spectra result shows that the intensity of(002) diffraction peak increases.when the molar ratio of PVP to zinc acetate increases from N1 to N5.The UV-vis spectra result shows that the absorption edge increases from 387 nm to 440 nm and the PL spectra result shows that the surface defect concentrations of Zn O nanorods decreases obviously.(4) Different length and diameter of Zn O nanorod arrays are synthesized by adjusting the water bath reaction time.The FESEM result shows that the average diameter of Zn O nanorods increases from 64 nm to 78 nm and the average length of Zn O nanorods increases from 0.36 μm to 1 μm respectively when the water bath growth time increases from t1 to t3.The XRD spectra result shows that the intensity of(002) diffraction peak increases with the increase of the water bath growth time from t1 to t3, which illustrates that Zn O nanorod arrays with the more perfect crystallinity have been synthesized gradually. The UV-vis spectra result shows that the absorption edge increases from 401 nm to 436 nm and the the PL spectra result shows that the density of the surface defect of Zn O nanorods reduces obviously.The red shifting of the PL curves from 585 nm to 604 nm demonstrats that the grain size of Zn O nanorods becomes large.(5) The formation mechanism of Zn O nanorod arrays has also been studied. Zn O nanorod arrays were synthesized through the seven processes of complexation,Zn(OH)2 formation, thermal decomposition, PVP carbonization, carbon thermal reduction, Zn oxidation and carbon removal. In the process of complexation, the protonation degree of PVP becomes higher when the PVP-Zn2+complex solution is positively charged. As a result, the complexation of PVP and Zn2+ becomes weaker because of the carbonyl which exists in PVP is negatively charged. While the protonation degree of PVP becomes rather weaker and PVP guides the quasi-one-dimensional orientation growth of Zn O nanorods when the PVP-Zn2+complex solution is negatively charged.