Research On Eu-doped Materials By Near Ultraviolet Excitation And Its Applications In Down-conversion Solar Cells And Warm White LEDs

Since the energy crisis,environmental pollution,and other issues becoming gradually aggravated,renewable energy technology and energy-saving technology researches are getting increasingly attention.The development and application of rare-earth ion doped materials are closely related to the development of high-tech materials.In this trend,combined with the current application needs of the industry and the urgent problems to be solved,this thesis mainly studies the related applications of europium ion doped materials in the field of down-conversion solar cells and warm white light emitting diodes(WLED),including the following two parts:Part 1:Application of Eu3+doped transparent glass in the field of down-conversion solar cellsCurrently,the main scheme of down-conversion solar cells is to apply spectral conversion materials on the surface of solar cells,but there is a contradiction in this scheme.Particularly,spectral conversion materials are opaque,if the size of the down-conversion materials is too small,the spectral conversion ability is limited While if the size of the down-conversion materials is too big,the obstruction of light is not conducive to the improvement of solar cell efficiency.There are also some attempts to develop glass materials,but there are no specific cases to effectively improve the efficiency of solar cells.In this paper,transparent glass based on Eu3+ ion doping was prepared and applied in the field of solar cells.The key problems of down-conversion solar cells were discussed,and the corresponding improvement ideas were proposed.The main achievements were as follows:(1)silicate glass with Eu3+ doped was prepared by high temperature melting method,and SiO2 glass with Eu3+doped was prepared by sol-gel method.These glasses can convert short-wavelength purple light into red light without affecting the transmittance to light of other wavelength.But with these glasses on the solar cells,the performance of solar cells was decline instead of improving.The reason for the decrease of solar cell efficiency is that the emission direction of Eu3+is random and a large number of red light escapes.Therefore,we need to consider solving problem of the energy loss caused by glass.Based on the research of other scholars,a surface micro-structure on the glass was designed in this paper.With software simulation by TracePro7.0 and experiments,it’s showed that the glass with micro-structure on the surface can restrict the light in the glass.The light irradiated to the glass surface can be reflected downward.(2)Subsequently,according to the above conclusions,two kinds of glass with micro-structures on the surface were designed and fabricated.It was found that the performance of solar cells could be improved by the application.When the glass surface is designed with an inverted pyramid triangular pyramid with an angle of 90°,the short circuit current of the solar cell can be increased and the efficiency can be increased by 0.41%.It was also been confirmed that the experimental of SiO2 glass with EU3+doped can get the same conclusion.When the glass surface is designed with a 60°positive triangular pyramid structure,the short-circuit current of the cell increases from 35.12 mA/cm2 to 36.92 mA/cm2,thereby increasing the efficiency of the solar cell from 14.17%to 14.68%.Compared with silicate glass,SiO2 glass with Eu3+ doped with the 60°positive triangular pyramid structure can improve the performance of crystal silicon cell better.Part 2:Optimization of phosphors with Eu2+doped and their applications in warm WLEDAt present,WLED in the market basically was usually prepared with yellow phosphor(YAG:Ce3+)excited by blue LED chip.It was found that the spectrum of red part is too little,the color rendering index is only about 75.The performance of the WLED with red and green phosphors excited by blue LED chip is improved,the luminous efficiency of the WLED is limited.The scheme of red,green and blue phosphors excited by purple chip is found has more advantages in color rendering index and luminous efficiency.In this paper,it was researched that the phosphor materials with Eu2+doped and its application in the filed of warm W LED.The main achievements are as follows:(1)Commercial red-green-blue phosphors with Eu2+doped were reviewed,the most efficient red,green,blue phosphors were selected that red phosphors(Sr,Ca)AlSiN3:Eu2+,green phosphors(Ba,Sr)2SiO4:Eu2+and blue phosphors Sr5(PO4)3Cl:Eu2+.A warm WLED was prepared with these selected high-efficient phosphors and excited by 395 nm near-UV chip,and with a not good performance.The reason is belong to the low efficient blue phosphor.Then the blue phosphor Sr5(PO4)3Cl:Eu2+was optimized from the synthesis process,raw materials.And a more efficient blue phosphor Sr5(PO4)3Cl:Eu2+was obtained.The optimized blue phosphor was applied to the fabricate of white LED.And also,the packaging method of phosphors was optimized by placed the blue phosphors on the top layer by layer,which reduced the secondary absorption of red and green phosphors.Then,the influence on the performance of LED with phosphors of different particle sizes was analyzed.Finally,the ratio of three color phosphors was adjusted,and a high efficiency warm white LED with different color temperature was obtained.Among them,when the LED with the color temperature is 3150K,warm white LED has the best luminescent performance.Its color rendering index Ra is 90.7,the related color temperature CCT is 3150K,and the CIE color coordinates is(0.4354,0.4196).The luminous efficiency reaches 104.86 lm/W,which meets the requirements for commercialization.(2)The human biological safety of light source was emphasizes in this paper,and phosphor was developed for warm white LEDs with the perspective of biological safety.In order to prepare warm WLEDs with high biological safety,a blue phosphor LiCaP04:Eu2+with near-ultraviolet excitation emission peak band of 470 nm has been developed.The emission spectrum of the phosphor avoids the hazard zone of blue light(450 nm band).And,the blue phosphor LiCaPO4:Eu2+ with great performance was obtained by optimizing doping concentration.A NUV excited warm WLED was prepared by using 395nm InGaN chip coated with red(Sr,Ca)AlSiN3:Eu2+,green(Ba,Sr)2SiO4:Eu2+,and blue LiCaPO4:Eu2+phosphors.The color rendering index(Ra)is 88.6,the correlation color temperature is 3351 K,and the color coordinates Locates at(0.4399,0.4389),the lumen efficiency is 77.051m/W.The performance of the prepared warm WLED have its unique advantages with the spectrum less in the hazard zone.(3)As well as,a full spectrum warm WLED with color rendering index(CRI)of 95.8 is fabricated by using 395-nm near-UV chip coated with Sr5(PO4)3Cl:Eu2+,LiCaPO4:Eu2+,(Ba,Sr)2SiO4:Eu2+,and(Sr,Ca)AlSiN3:Eu2+phosphors.The correlation color temperature is 3527K,the color coordinate is(0.4125,0.4067),and the luminous efficiency is 40.311m/W.The white light emission spectrum of the prepared full-spectrum LED covers the whole visible band from 420 to 650 nm,which is rich in color and excellent in color rendering.