Investigations Of Down Conversion Materials Used For Warm White LEDs And Polycrystalline Silicon Solar Cells

Currently,the commercial white light emitting diodes?W-LEDs?are made using a blue GaN-based chip with a yellow-emitting YAG:Ce3+ phosphors.However,the disadvantages of this approach lead to nonuniform white light,high correlated color temperature,low color-rendering index and especially featuring redundant blue light may damage human eyes,which result in unsuitable for the indoor lighting applications.A promising alternative approach for generating warm W-LED for indoor lighting application is by pumping tricolor phosphors?blue,green and red?with near-ultraviolet?near-UV?chips.One key point of this approach is to develop the efficiency,near-UV pumped down-conversion?refer to accord with the "Stokes"conversion rather than quantum cutting?tricolor phosphors.On the side,owing to the restriction of band gap width of Si,the utilization of sunlight at wavelength blow 420 nm is low.As a result,using the down-conversion tricolor phosphors,which can efficiently be pumped near-UV light,to enhance the performance of the crystal Si cell become a research hotspot in the photovoltaic area.In the present study,down-conversion tricolor phosphors for warm W-LED and down conversion solar cell application were investigated and the results concluded as follows:Part 1:Near-UV pumped down-conversion tricolor phosphors for warm W-LED applicationIn this paper,rare earth doped borate,phosphate down-conversion tricolor phosphors for warm W-LED application were synthesized via high-temperature solid-state method;those phosphors were classified into two categories based on the different of luminescence principle.One is based on 4f-4f transitions,another is based on 4f-5d transitions,the results concluded as follows:?1?:Rare earth?RE= Tm3+,Tb3+,Eu3+,Dy3+,Sm3+?single-/co-doped KMgBO3 and NaBaBO3 down-conversion tricolor phosphors for warm W-LED application were synthesized via high-temperature solid-state method,the preparation and luminescent properties of this type 4f-4f transition based phosphors were investigated.For rare earth doped KMgBO3 system,a series of rare earth doped Ce3+,Tm3+,Tb3+,Dy3+ and Eu3+ doped KMgBO3 phosphors were synthesized high viatemperature solid state method.The CIE chromaticity coordinates of Ce3+,Tm3+,Tb3+,Dy3+ and Eu3+ doped KMgBO3 phosphors were calculated to be?0.169,0.016?,?0.146,0.062?,?0.258,0.537?,?0.634,0.356?and?0.280,0.304?,which located in purple-blue,blue,green,white and red area respectively.In particular,the color purity of Ce3+,Tm3+and Eu3+ doped KMgBO3 phosphors was calculated as high as 98.0%,94.0%,and 97.0%.The results demonstrate that rare earth doped KMgB03 samples are both good candidates for near-UV pumped tricolor phosphors.For rare earth doped NaBaBO3 system,a series of rare earth doped Tm3+,Tb3+,Sm3+,Dy3+ doped and Dy3+,Eu3+co-doped NaBaBO3 phosphors were synthesized high via temperature solid state method,Tb3+ doped NaBaBO3 phosphor can be pumped by 377 nm near-UV light and birthed 543 nm green light,this phosphor features good thermal stability,activate energy of thermal quenching is calculated to be 0.113 eV;Sm3+ doped NaBaB03 can emit the highest 560 nm yellow light when excited by 403 nm due to the asymmetric substitution;By optimize the concentration of Dy3+ and charge compensator K+,NaBaBO3:Dy3+,K+ has been demonstrated to be a single-phase white emitting phosphor;The CIE chromaticity coordinates of Ce3+Tm3+,Tb3+,Sm3+ and Dy3+ doped NaBaBO3 phosphors were calculated to be?0.1470,0.1090?,?0.2860,0.4640?,?0.4760,0.5090?and?0.3010,0.3080?,which located in blue,green,yellow and white area respectively.Through co-doping Eu3+ to NaBaBO3:Dy3+,the correlated color temperature?CCT?can be improved by control concentration of Eu3+.Finally,white emitting with CIE chromaticity coordinate of?0.332,0.315?and relative low CCT of 5514.31 were obtained.?2?:Eu²⁺ doped SrB2O4,Cas?PO4?3Cl and Srs?PO4?3Cl down-conversion tricolor phosphors for warm W-LED application were synthesized via high-temperature solid-state method,the preparation and luminescent properties of this type 4f-5d transition based phosphors were investigated.For Eu²⁺ doped SrB2O4 phosphor,blue emitting with 97%color purity could be obtained when SrB2O4:Eu²⁺ pumped by near-UV light;This phosphor can be effectively excited within the broad near-UV wavelength region from 270 to 350 nm and feature a satisfactory blue-emitting?peaking at 448 nm?performance due to the 4f-5d transitions of Eu²⁺ ions.For Ca5?PO4?3Cl:Eu²⁺ phosphor,Ca5?PO4?3Cl:Eu²⁺blue-emitting phosphor was prepared via a high-temperature solid-state reaction method.The Ca5?PO4?3Cl host was calculated to be a wide indirect band gap of approximately 5.30 eV by density functional theory.Ca5?PO4?3Cl:Eu²⁺ could be efficiently excited by 260-420 nm near-UV light and feature a board emission from 400 to 530nm and peaking at 456nm,the optimized Eu²⁺ concentration is 2mol%and the concentration quenching mechanism can be explained by the dipole-dipole interaction.A near-UV white LED was fabricated using a 395 nm InGaN-based near-UV LED chip in combination with Ca5?PO4?3Cl:Eu²⁺ phosphor,Eu²⁺ doped green phosphor,and Eu²⁺ doped red phosphor,the excellent color rendering index of 96.65 at a CCT of 3902 K with CIE coordinates of?0.3952,0.3790?was obtained for the fabricated near-UV pumped W-LED when driven using a current of 350 mA and a voltage of 3.29 V.For Sr5?PO4?3Cl:Eu²⁺ phosphor,Eu²⁺ doped Sr5?PO4?3Cl blue-emitting phosphor was prepared by high-temperature solid-state reaction method.Sr5?PO4?3Cl host was calculated to be a wide indirect band gap of approximately 5.01 eV from the top of valence band at M point to the bottom of conduction band at ' point by density functional theory.Sr5?PO4?3Cl:Eu²⁺ could be efficiently excited by 250-400 nm near-UV light and feature a board emission from 410 to 490 nm and peak at 444 nn,the color purity was deterUined to be 99%,the optimized Eu2 concentration is 1 mol%and the physical mechanism of concentration quenching can be explained by the dipole-dipole interaction.It can be found that the emission intensity measured at 150 ? drops to 87.61%of the initial value measured at 27 ? and the activating energy of thermal quenching is calculated to be 0.113 eV,demonstrating this phosphor feature a good thermal stability.A near-UV white LED was manual fabricated using a 395 nm InGaN-based near-UV LED chip in combination with Sr5?PO4?3Cl:Eu²⁺phosphor,Eu²⁺ doped green phosphor,and Eu²⁺ doped red phosphor,the excellent color rendering index of 94.65 at a CCT of 3576 K with CIE coordinates of?0.3952,0.3790?,with the luminous efficiency of 33.25 lm/W was obtained for the fabricated near-UV pumped W-LED when driven using a current of 350 mA and a voltage of 3.29 V.Furthermore,the device using a 395 nm InGaN-based near-UV LED chip in combination with Srs?PO4?3Cl:Eu²⁺ phosphor,Eu²⁺ doped green phosphor,and Eu²⁺doped red phosphor,mechanical fabricated by Xiamen Hualian Elec.Co.,Ltd shows the high luminous efficiency of 80.87 lm/W in 2016.The results demonstrate a warm white LED can obtain by near-UV chip pumped tricolor phosphors.Part 2:Near-UV pumped down-conversion tricolor phosphors for warm W-LED applicationIn this paper,Rare-earth doped and rare-earth free vanadate down-convention nano phosphors for the application in polycrystalline Si area were synthesized by hydrothermal method.The results concluded as follows:?1?:The YVv4:Eu3+,Bi3+ down-conversion nanoparticle synthesized by a hydrothermal metihod was firstly applied in polycrystalline silicon solar.The nanoparticles are ranging from 20 to 40 n,YVO4:Eu3+,Bi3+.can be efficiently excited by 200-350 nm,which attribute by the transition of 02--V5+in VO43-,and emit the red light with a peak at 620 nm.By spin coating different concentration YVO4:Eu3+,Bi3+ colloid on polycrystalline silicon solar,the results show that both high and low concentration colloid cannot efficiently improve the performance of silicon solar cells.The YVO4:Eu3+,Bi3+ colloid concentration with 5 mg/ml gave the best improvement of polycrystalline silicon solar.The short-circuit current density Jsc increased from 35.99 mA/cm2 to 37.09 mA/cm2,efficiency increased from 14.71%to 15.14%,net efficiency increased by 0.43%.EQE result confirmed that the improvement of Jsc was attributed to down-conversion effect.The results demonstrate that YVO4:Eu3+,Bi3+ down-conversion nanoparticle can efficiently improve the performance of polycrystalline silicon solar.?2?:Rare earth doping-free Zn3V2O8 down-conversion nanoparticle synthesized by a hydrothermal method was firstly applied in the solar cell area.The nanoparticles are ranging from 20 to 30 nm.Zn3V2O8 down-conversion nanoparticle could efficiently convert the near-UV light from 200-400 nm to 450-600 nm?peaking at 560 nm?.By spin coating 5 mg/ml Zn3V2O8 down-conversion nanoparticle colloid which dissolved in ethanol on polycrystalline silicon solar,the results show that the short-circuit current density Jsc can be efficiently improved from 33.12 mA/cm2 to 33.92 mA/cm,while the fill factor FF and open circuit voltage Voc remain unchanged,net efficiency increased by 0.32%from 13.19%to 13.51%.A remarkable improvement in the near-UV area from EQE result demonstrates that the promotion of Jsc results from down-conversion effect.This work demonstrated that the polycrystalline silicon solar could be efficiently improved by rare earth doping-free down-conversion materials.