Study On The Luminescence Properties Of Rare Earth Doping Material And Its Application In Solar Cells And White LEDs

Rare earth ions are widely applied in down conversion solar cell and near-ultraviolet(n-UV)excitation warm white LED,since it can convert n-UV into visible light.Firstly,photovoltaic glass,doped with rare earth ion Eu3+,with down-shifting function was developed.Moreover,photovoltaic glass with compound eye structure was researched.Secondly,the Ce3+ and Yb3+ doped CsPbClxBry(x+y=3)perovskite quantum dot material was coated on the surface of the crystalline silicon solar cell,so that the photoelectric conversion efficiency(PCE)was improved.Thirdly,a novel stable Eu-doped Na2Al2B2O7(NAB:Eu)bicolor phosphor excited by n-UV has been successfully prepared by one-step solid state process in air.The self-reduction of Eu3+?Eu2+ in NAB has been realized.The luminescence properties have been analyzed,as well as the application in White LED has been explored.The main works of this paper are as follows:(1)Development of Eu3+ doped photovoltaic glass and compound eyes structure photovoltaic glass:The Eu3+ doped calcium-sodium photovoltaic glass was developed by high-temperature sintering method.The excitation spectrum,emission spectrum and transmittance were characterized.It obeys the discipline of f-f transition of Eu3+ that exhibits a red emission at 612 nm under the excitation of n-UV with peak at 393 nm.The optimum content of Eu3+ is 0.02 in molar concentration.The PCE of the crystalline silicon solar cell increases by 0.16%when covered by the Eu3+ doped photovoltaic glass.In addition,a special designed photovoltaic glass with a compound eye structure has been explored to improve the PCE of solar cell.Optical simulation is carried out through the Trace Pro ray tracing software.The influence factors include the arrangement gap length(D),the chord ratio(L/H)and the size of compound eyes(R).Comparing to the conventional flat photovoltaic glass,the compound eyes photovoltaic glass has an increment of 6.41%on collecting sun energy,when the compound eyes arrange gapless with the L/H of 2.5 and R of 20.50mm.Experimentally,the compound eyes photovoltaic glass samples fabricate with D of 0.584 mm,L/H of 2.5,and R of 4.1mm,and cover on a 6.25cm2 crystal silicon solar cells.A fully daytime photocurrent test in Xiarmen was carried out by covering the photovoltaic glass on crystalline silicon solar cell.When sunlight is slanting in the early morning and later afternoon,the photocurrent increment of solar cell covered by the compound eyes glass achieves 8.9 mA in maximum.The absolute PCE increment of the as fabricated compound eyes photovoltaic glass is 1.03%in maximum,by comparing to that of the conventional flat photovoltaic glass.Moreover,the compound eyes glass does not cause obvious temperature rise.Therefore,the compound eyes glass provides a promising enhancement on sunlight collection for PV modules.(2)Study on rare earth doped perovskite quantum dots and their application in silicon solar cells:CsPbCl3,CsPbCl1.5Br1.5 and CsPbBr3 perovskite QDs were prepared by thermal injection.The energy gaps were 3.75 eV,2.72 eV and 2.42 eV,respectively.Thereof,two kinds of QDs of CsPbCl1.5 Br1.5:Ce3+(3%)and CsPbCl1.5 Br1.5:Ce3+(1%),Yb3+(2%)were prepared.The photoluminescence spectra showed that the energy transition from CsPbCl1.5Br1.5 to Ce3+ ion was achieved and quantum cutting was realized by codoping of Ce3+ and Yb3+.When spin coating the above QDs on polycrystalline silicon solar cells,the PCE was increased by 0.4513%and 0.508%,respectively.Further,a diamond-like carbon film was deposited on the spin-coated QDs for protection,but results in a reduction in PCE.(3)Study on Luminescence Properties of Self-reducing Na2Al2B2O7:Eu Phosphors and Its Application in White LEDsRecently,it has been found that the self-reduction mechanism can reduce high-valent rare earth ions into low-valent under air atmosphere,and realize transitions of both f-f and 4f-5d,which is significant in theory and application prospects.We conducted a novel study on the self-reduction Na2Al2B2O7:Eu phosphors by traditional solid state reaction in air.It is found that the emission peak at 445 nm is derived from the 4f65d1?4f7 transition of Eu2+,and the emission peak at 570-650 nm belongs to the transition of 5D0?7FJ(J=0,1,and 2)from Eu3+.The ESR and XPS confirmed the presence of Eu2+ in Na2Al2B2O7.And the self-reduction process is explained by the principle of charge compensation.The phosphor has an excellent thermal stability in red emission and no fluorescence quenching occurs.The emission intensity increases with the Eu doping concentration,and the second phase Eu(BO3)was determined in the XRD patterns.However,the emission strength at 445nm shows different variation trend with the increment of Eu doping concentration,which is neither concentration quenching nor uniform changing,but gives two remarkable peak values.The PL quantum efficiencies of Na2Al2B2O7:0.16Eu sample are 11.99%and 9.39%with the excitation of 341nm and 393nm,respectively.The intensity balance between the blue emission of Eu2+ in Na2Al2B2O7 and the red emission of Eu3+ in Eu(BO3)can be achieved by changing the excitation wavelength,and the corresponding CIE coordinates can also be varied.Finally,LEDs were made by coating the as prepared Na2Al2B32O7:0.16Eu phosphor on a 385 nm chip.The color coordinates are consistent with the simulation data.The lumen efficiency of the LED is 0.99 lm/W,the color temperature is 2204 K,and the color rendering index is 34.9.