| Dye sensitized solar cells(DSSCs)have been the focus of scientific research because of their advantages on simple production,high efficiency,clean and pollution-free.The solar light utilization rate of traditional DSSCs is still low.And spherical nanocrystalline TiO2 only absorb less than 387 nm of ultraviolet light with limited electron transfer effect.Which lead to a low photoelectric conversion efficiency.As a new member of the carbon family,carbon quantum dots(CDs)have attracted more and more attentions because of their low toxicity,small particle size,excellent fluorescent properties,and electronic media.Consequently,the introduction of carbon dots and different morphology TiO2 into dye-sensitized solar cells not only leads us towards a new step to a sustainable green development,but also solves the problem of low DSSCs photoelectric efficiency.Based on the above discussion,the main research work of this paper as follows:By using maleic anhydride and o-,m-,p-phenylenediamine as the raw materials,RGB carbon dots with good fluorescence properties were prepared by solvothermal method.9 kinds of carbon dots were prepared by changing the reaction time(4,12,20 h).The surface functional groups,structure,size and optical properties etc of carbon dots were characterized by IR,XPS,TEM,UV-vis,PL and other testing methods.Their fluorescence quantum efficiency is proposed,and the highest one is 31.8% with the reaction condition: 0.216 g m-phenylenediamine,0.216 g maleic anhydride,12 mL ethanol,the reaction temperature is 200 ?,the reaction time is 4 h.The stability of fluorescence was studied by the fluorescence intensity and luminous range with the various concentrations of carbon dots.The PL intensity increases first and then decreases in concentrations of carbon dots from 10-5 g/L to 1 g/L.And the maximum PL intensity was obtained in the concentration of 10-3 g/L.Only blue fluorescence was shown at low carbon dots concentrations.Higher concentrations of carbon dots lead to a red fluorescence.The effects on the photovoltaic performance of DSSCs modified by RGB carbon dots were explored through I-V curves,it is found that the efficiency of cells modified by Green CDs was increased from 6.87% to 7.20%,and the short-circuit current was increased from 15.09 mA/cm2 to 16.10 mA/cm2.In order to enhance the spectral response of DSSCs,carbon dots with absorbing blueviolet and emitting blue-green light are introduced into DSSCs.The morphologies,structures and optical properties of ethanol soluble blue-green carbon dots were characterized by TEM,XPS and PL.After modification of DSSCs photoanode by carbon dots,the influence of carbon dots on light absorption and the carrier transfer behavior(transmission and composite)of the internal battery cell were studied through photoelectrochemical method such as IPCE,EIS,I-V curve,and so on.And the reasons for the improvement of photoelectric conversion efficiency were analyzed.The experimental results show that the particle size of the blue-green carbon dots is around 3-5.5 nm,which can be assigned to the structure of nitrogen oxide graphite,and with a large number of nitrogen-containing oxygen functional groups on the surface.Bluegreen carbon dots show good fluorescence properties.After modification of DSSCs photoanode by carbon dots,the utilization ratio of N719 to sunlight is improved by light conversion.Meanwhile the path of electron transport is shortened.Thus,as a result,the photocurrent density of the cells increased significantly from 16.12 to 21.26 mA/cm2,and the photoelectric conversion efficiency of the cells increased from 7.25% to of 8.70%.TiO2 nanotubes,nanorods and flower-like TiO2 were prepared by solvothermal method,and were constructed as double layer structure with P25.The morphology,crystalline phase and particle size of them were investigated by SEM,XRD and so on.And their photoelectric properties were studied by UV-vis,diffuse reflectance,I-V curve and other test methods.EIS,OCVD and other electrochemical methods were used to discuss the carrier transfer behavior and the electronic lifetime of the flower-like TiO2 nanoparticles and the blue-green carbon dots co-modified cells.The results show that flower-like TiO2 particles were rutile phase with a diffuse reflection in 434-800 nm.The flower-like TiO2 is more suitable for using the light diffusion layer and constructing the double layer structure with P25.They make not only the photocurrent increase to 16.7 mA/cm2,but also the photovoltage to 0.751 V,respectively.In general,the photoelectric conversion efficiency of solar cell is increased from 7.08% to 7.69%.Flower TiO2 nanoparticles and blue-green carbon dots co-modified DSSCs photoanode.Which combine light conversion affect of blue-green carbon dots with light scattering and electrical transport affect of flower-like TiO2.As a result,the photoelectric conversion efficiency of solar cell is increased from 7.08% to 8.11%(increased by 14.5%),The shortcircuit current is increased from 15.7 to 17.8 mA/cm2(increased by 13.4%). |
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