A Study On TiO₂-ZnO Composite Dye Sensitization Thin-film Solar Cell

Nowadays, the crisis of energy has became the block of society development, then the exploitation of new energy was extremely urgent. So the solar cell has became the focus of research.The preparation of dye sensitization thin-film solar cell has became the popular topic because of its advantages such as simple technology, high stability, long lifetime and low price.TiO₂-ZnO composite films used in dye sensitization thin-film solar cell were prepared by sol-gel method, and were analyzed by TG-DTA, XRD, SEM, TEM and UV-Vis absorbance spectrum.TiO₂-ZnO composite sols with diferrent Ti/Zn mol ratio were prepared by butyl acetate titanate and zinc acetate used as precursor,and the phase composion and microstructure were tested by TG-DTA,XRD and SEM.The best Ti/Zn mol ratio were discussed in the research.The results showed that the composite sol with Ti/Zn (mol ratio)=3:1 fired at 500℃had two kinds of crystals:anatase and partial zinc titanate,the crystalinity and the sizes of which were 94.8%,94.9% and 23.771nm,62.649nm respectively.The appearance of Ti-Zn sosoloid couldn't be avoided because of the contact of Zn2+ and butyl acetate titanate at molecular level.Because partial zinc titanate had high dielectric contant and anatase had good photoelectric effect,so Ti/Zn(mol ratio)=3:1 was chosen as the best mol ratio.TiO₂-ZnO composite thin-films were prepared on the slides by spinning coating method,and were tested by SEM and UV-Vis absorbance spectrum.The influence of the way of heat-treatment,the amount of sol per layer, the viscosity of the sols,the treatment of the slides and the way of film coating to the properties of thin-films were discussed in the research.The structure of the samples were analyzed by XRD and UV-Vis absorbance spectrum.The results showed that transparent and complete composite films could be prepared when the way of heat-treatment was step-by-step way (the method of cycle:one layer of film, then one time of heat-treatment),the temperature was controlled at 550℃,uncorrupted slide was chosen as the matrix,the viscosity of sols were controlled at 30 drops per layer and the amount of layer was chosen as 3.When the way of heattreatment was single-step (the method:many layers of films, then one time of heat-treatment), the thin-film would craze and fall off. The thin-films prepared by composite sol had the thickness of 1.0μm,and the surface with the distribution of particles,the size of which was about 0.1μm.It had the highest absorbance of 3.9 when the wavelength was 300nm. The thin films prepared by layered sol had the thickness of 0.7μm, the surface covered densely of the structure of three-dimensional net because of the growth in vertical direction of T-ZnO crystal in the form of four claws, the width of net was 0.1μm, the new absorption boundary appeared between 320nm-500nm because of the coupling effect between TiO₂ particles and ZnO particles and the highest absorbance of 0.25～3.2.In order to increase the thickness of thin-films, the sol had been tried to coat on the slide corrupted by 5%HF for 30s, the results showed that this way had little influence to the thickness of thin-films and would decline the transparency of the slides.TiO₂ sol with doped Zn2+ and La3+ and ZnO sol with doped Al3+ and Li+ has been prepared and the TiO₂-ZnO composite thin-films with doped ions were prepared by compounding this two kinds of sols.The mechanism of doped ions to the microstructure and UV-Vis absorbance of samples were discussed.The results showed that the thin-films with doped ions all had the transparent and complete appearance, because small amounts of doped ions wouldn't change the appearance of samples in macro, but could improve the absorbance of light.The samples prepared from composite sol with the doped ions, the amount of which were Zn (0.6)-La (0.4),Al(1.0)-Li(2.0), had the surface with sparse grains, the size of which was 0.1μm.The sample had the thickness of 0.8～1.0μm, and had the highest absorbance of 4.1 when the wavelength was 290nm.The absorption threshold of the sample fell to 336.38nm, and the band gap rised to 3.68eV because of the doped ions, the phenomenon was beneficial to separate the conductive holes and electron.The samples prepared by layered sol with the doped ions, the amount of which were Zn (0.2)-La (0.4),Al (1.0)-Li (2.0), had the sample covered densely with the structure of three-dimensional nets because of the growth in vertical of T-ZnO crytal in the form of four claws and the width of net of 0.3μm.There were some sheet connection and porous structure between the nets because of the expansion of lattice caused by doped La3+.The thickness of the sample was about 0.8μm～1.0μm.The sample had the highest absorbance of 3.9 when the wavelength was 300nm, The absorption threshold of the sample fell to 355.47nm, the energy gap rised to 3.49eV because of the doped ions, and the probability of compound of electronics and holes would decline.Because of the coupling effect between TiO₂ particles and ZnO particles, new absorption boundary appeared when the wavelength was 320nm.