| Solar energy is a renewable energy which will not be exhausted,and also it is a clean energy which will not produce any pollution.One of the main methods of solar energy utilization is solar photovoltaic power generation. With increasingly wide range of today’s solar power generation and its application,it has been gradually applied in the oil and gas development projects and provids services for the oil and gas fields.Dye sensitized solar cell (DSSC),the third generation of solar cell,has received more and more attention in recent years for its many advantages such as simple preparation procedure,high conversion efficiency and low cost, which make it become a promising new photovoltaic cells.Up to now, many scholars at home and abroad have carried out a lot of research work,and have made some achievements,but many problems still exist in its application for DSSC.For example,due to the wide band gap, TiO2can only absorb light of the ultraviolet region, which results in insufficient utilization of the incident light and seriously affects the photon-to-electron conversion efficiency of the DSSC.Nano-TiO2thin film as an important part of DSSC is one of the key factors for limiting photon-to-electron conversion efficiency of solar cell. Therefore, in the future, around the research on diversification of preparation technology of TiO2thin film, it is important to adjust the band gap of nano-TiO2,and expand its spectral response range to improve its sunlight utilization in the field of DSSC study.These researches have very important applicational and theoretical values.Based on nano-TiO2thin films as the research object,five kinds of methods such as cathodic electrodeposition method,anodic oxidation method,low thermal solid-state method,sol-gel and hydrothermal method had succeeded in preparing nano-TiO2powders and thin films,respectively.Then the nano-TiO2thin films were applied to DSSC.We used AFM,SEM,XRD,TG-DSC and XRF to characterize the morphologies, phase structure,composition and thermal properties of the nano-TiO2thin films.and analysed the effects of preparation process parameters on the morphologies and thermal properties of product.More over,its formation mechanisms of the part of the product are concluded.In addition,the characteristics of current-voltage curves (I-V curves) and AC impedance spectroscopy (EIS spectra) were studied for a variety of TiO2thin film materials,and the photoelectric properties of its cell were evaluated.The main research conclusions are shown as follows:(1) Nano-TiO2thin films were prepared by the cathodic electrodeposition method.The changes of process conditions such as voltage,pH and time during the preparation of TiO2thin films are discussed through single factor analysis method. Then the best formula and process conditions were achieved when Ti(SO4)2was used as titanium source,which included10.0mL of Ti(SO4)2,3.0mL of H2O2,2.0mL of HNO3,8.0mL of NH3·H2O,20.0mL of H2O,pH of1.5,the voltage of3.5V, depositing time of20min.Under this condition.a layer of uniform TiO2thin film formed and its TiO2crystal is anatase type, its size is10nm. The photon-to-electron conversion efficiency is up to1.26%. Fe-doped TiO2thin films are prepared by wet impregnation methods, its conversion efficiency can reach1.53%,increasing by21.4%.(2) TiO2nanotube thin films were prepared by the anodic oxidation method.Effects of anodic oxidation parameters on the morphology of TiO2nanotubes were studied in a aqueous solution containing F" ions as the electrolyte.When the voltage is less than15V, it does not favor the growth of TiO2nano tubes.When the voltage range is15-30V, the diameter of TiO2nanotubes also increases with the voltage increases.When the voltage reaches30V, the nanotube structures are destroyed and form a spongy-like porous structure with no rules. Therefore, it is conducive to the formation of large aperture TiO2nanotubes while the voltage is appropriately increased.Under the condition of voltage20V and oxidation time30min, the crystal of TiO2nanotubes is anatase phase, the diameter of TiO2nanotubes is around100nm, the photon-to-electron conversion efficiency of its cell was up to1.42%. After TiO2nanotubes are treated by using TiO2solution, the photon-to-electron conversion efficiency of its cell reaches1.98%, increasing by39.4%. AC impedance experiment results validated the conclusion.(3) Ni-doped TiO2thin films were prepared by the low thermal solid-state method plus screen printing technique.Ni-doped TiO2powders and thin films were prepared by direct solid phase reaction of butyl titanate and nickel chloride hexahydrate.The determination of Ni content is1.66wt.%.Ni-doped TiO2thin films prepared are not only spongy porous structure but also uniform film,its crystal is anatase type,and the average grain size is around20nm.Compared with undoped TiO2thin films, Ni-doped TiO2thin films promote the grain refinement.The photon-to-electron conversion efficiency is up to2.13%, increasing by about37.4%.The photon-to-electron conversion efficiency is further improved after TiO2solution treatment, its conversion efficiency is2.45%.(4) TiO2nanocrystalline thin films were prepared by the sol-gel method plus dip-coating technique.The best formula of reagents for the preparation of TiO2thin films was obtained by the orthogonal test method,which consists of10.OmL butyl titanate,50.0mL anhydrous ethanol and2.0mL nitric acid,1.0mL water,0.4g polyethylene glycol (20000).In this condition, uniform surface structure with no cracks is obtained in TiO2film.The average grain size is around12nm, and the film supplies photon-to-electron conversion efficiency of3.72%under100mW/cm2simulated sunlight irradiation.At the same time,La-doped TiO2thin films was prepared on the basis of the best formula.The results showed that Crystal phase of La-doped TiO2films prepared at450℃is anatase by XRD test.In La-doped TiO2crystal film,diffraction peaks become broader and their relative intensity decreases with the increase of doping molar content of La/Ti.Morever,it contributes to causing grain refinement and suppressing the grain growth, and photon-to-electron conversion efficiency also increases with the increase of doping molar content of La/Ti (0-1.5mol%).When La-doped molar ratio was1.5mol%, the photon-to-electron conversion efficiency reaches4.35%,and it increases as much as16.9%compared with no La in DSSC.In addition,mechanism analysis of La-doped TiO2thin film shows grain refinement and impurity energy level cause mainly the increase of photon-to-electron conversion efficiency.(5) Anatase TiO2nanocrystalline thin films were prepared by the hydrothermal method plus screen printing technique.Preperation formulations of TiO2powder was the mixture of10.0mL of tetrabutyl titanate,1.0mL water,and2.0mL of hydrochloric acid (37wt.%HCl) in40.0mL of anhydrous ethanol by the hydrothermal method.The optimum process condition of the preparation of TiO2thin films was obtained by the orthogonal test method.It included hydrothermal temperature of220℃, hydrothermal time of24h, printing layers of5layers, and heat treatment temperature of550℃.The TiO2thin films prepared in the optimum process conditions,as a photoanode,can supply a photon-to-electron conversion efficiency of5.53%.At the same time, rare-earth (Er,Yb) doped TiO2thin film was prepared on the basis of this formula.The results show that rare-earth (Er,Yb) doped TiO2thin film is spongy porous thin film with uniform distribution, and shows grain refinement compared with undoped TiO2thin film.When Er/Yb co-doped molar ratio is0.5mol%Er and0.5mol%Yb respectively,the photon-to-electron conversion efficiency is up to6.15%,increasing by11.2%than undoped TiO2thin film, which is consistent with AC impedance experiment result.(6) Photoanode TiO2film is a key component of DSSC,and it is the key of the improvement of the cell photon-to-electron conversion efficiency.It has an important influences on photovoltaic performance of solar cells.According to the study on diversification preparation and Modification of TiO2thin film,its results were shown as follows:TiO2film with uniformity was prepared by the cathodic electrodeposition method, and this methods have certain characteristics.but photon-to-electron conversion efficiency of the cells was lower;as for anodic oxidation methods,TiO2nanotube arrays were prepared by adjusting the factors such as oxidation voltage,electrolyte concentration, pH and oxidation time,and we predicted it might have a lot of improvement room for photon-to-electron conversion efficiency of the cell;TiO2thin films with spongy porous structure were prepared by low thermal solid-phase method with the advantages of a simple preparation process,less pollution,cheap and mass production.Photon-to-electron conversion efficiency of its cell is still lower,there is improvement room for its photon-to-electron conversion efficiency after continuing to be studied.This method is adaptable,and it is one of very promising preparation methods;there are the advantages of simple equipment, easy to control and easy to industrial production for sol-gel method.TiO2thin film prepared by using this method is more uniform,and photon-to-electron conversion efficiency of its cells is still lower.thus,it needs further research to improve photon-to-electron conversion efficiency;TiO2thin films with spongy porous structure were prepared by the hydrothermal method plus screen-printing technology.Its cell has higher photon-to-electron conversion efficiency, and there are good prospects for industrial production.In addition,after the processing of the modified TiO2thin film prepared by the aforementioned methods,photon-to-electron conversion efficiency of its cell can be increased to some extent.Therefore,it is a very effective method for TiO2film modified to improve photon-to-electron conversion efficiency of its cell. |
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