Study On The Preparation And Properties Of Carbon Dots Based Luminescent Solar Concentrators

Luminescent solar concentrators(LSCs)have attracted extensive attention due to their potential application in Building Integrated Photovaltaic(BIPV).They can not only replace expensive solar cells with large-area LSCs to reduce the cost,but also avoid the thermal effect caused by direct sunlight on photovoltaic devices when they are applied to BIPV.In addition,the color and shape of LSCs can be adjusted and controlled,which can not only decorate buildings,but also be combined with other functional materials to make multi-functional smart windows.Although carbon quantum dots with low cost,easy preparation,good stability and high fluorescence quantum yield have received much attention,reports on their application in LSCs are rare.In this paper,carbon quantum dots are proposed as fluorescent material,and eco-friendly polyvinylpyrrolidone(PVP)which has very good compatibility with carbon quantum dots are used as polymer film.In addition,glasses with different refractive indexes are firstly introduced as substrates to prepare thin film LSCs.The effect of carbon concentration,the layers(thickness)of thin films and the substrate refractive index on photoelectric properties of thin film LSCs are investigated,respectively.The main conclusions are as follows:(1)The carbon quantum dots prepared by microwave method had uniform particle size distribution and good dispersion,and the particle size was mainly between 2-5 nm.The presence of the surface hydrophilic group group made it have a good water solubility,and the strong electron donor groups such as amino group and carboxyl group can also greatly improve the fluorescence performance of the carbon point.The absorption peak of carbon point was about 350 nm,and it can absorb light in the range of 300-500 nm.When the carbon point was stimulated by the optical excitation in the range of 290-500 nm,the fluorescence emitted by the carbon point will showed a significant red shift with the increase of the excitation wavelength due to the dependence of the excitation wavelength.(2)The surface of the CDs/PVP composite film prepared by spin-coating was smooth and flat,and the connection between the film and the substrate was tight,without bubbles or gaps.The transient fluorescence spectra and fluorescence emission spectra of the film samples were consistent with the test results of carbon dots in ethanol solution.As the concentration of carbon dots and the layers(thickness)of thin films increases,the absorption and fluorescence emission intensity under the same excitation wavelength of thin film samples both increased,but the photoelectric conversion efficiency of LSCs increased at the early stage and then decreased,and photoelectric performance of the CDs/PVP composite thin-film LSCs with 7 layers(0.5 wt%)was the best,the photoelectric conversion efficiency of which was 4.97%,optical efficiency of which was 5.02%.(3)CDs/PVP composite thin film LSCs were prepared on substrates with a refractive index of 1.45,1.51 and 1.61 by spin-coating.The photovoltoic properties of each sample were tested,and it was found that with the increase of the substrates' refractive index,the photoelectric performance parameters of the thin-film LSCs were significantly improved.Taking the film with 5 layers as an example,the photoelectric conversion efficiency of the LSC with the substrate refractive index of 1.61 was nearly 1.3 percentage points higher than that of the LSC with the substrate refractive index of 1.45.