A series of Y2.985Al5–xGaxO12:0.015Ce(YAGG:Ce,x=0,1,2,3,4,5)transparent ceramics were prepared via a solid-state reaction method.Two-step sintering technique was proved to be an effective approach to prepare function...A series of Y2.985Al5–xGaxO12:0.015Ce(YAGG:Ce,x=0,1,2,3,4,5)transparent ceramics were prepared via a solid-state reaction method.Two-step sintering technique was proved to be an effective approach to prepare functional ceramics with high Ga concentration,and Y3Ga5O12(YGG)transparent ceramic was successfully prepared for the first time.According to the variation of Al/Ga ratio,regulation of band structure and luminescence properties of YAGG:Ce transparent ceramics were effectively investigated.When Ga substitutes Al sites,the tetrahedral site is more favorable compared to the octahedral site for Ga to occupy according to the first-principle calculation.A continuous blue shift of the emission from 565 to 515 nm was achieved as Ga was gradually introduced into Y3Al5O12:Ce matrix.High quality green light was obtained by coupling the YAGG:Ce ceramics with commercial blue InGaN chips.Transparent luminescence ceramics accomplished in this work can be quite prospective for high power LED application.展开更多
Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes(OLEDs),which adopt luminescent radicals as emitters,aiming at improving the external quantum efficiency(EQE)of OLEDs.Research...Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes(OLEDs),which adopt luminescent radicals as emitters,aiming at improving the external quantum efficiency(EQE)of OLEDs.Research on luminescent radicals and the corresponding devices is a multidisciplinary field involving organic chemistry,solid-state physics,photochemistry,electronics,and others.The relevant theories have been established step-by-step in recent years.展开更多
While the demand for deep ultraviolet(DUV)light sources is rapidly growing,the efficiency of current AlGaN-based DUV light-emitting diodes(LEDs)remains very low due to their fundamentally limited light-extraction effi...While the demand for deep ultraviolet(DUV)light sources is rapidly growing,the efficiency of current AlGaN-based DUV light-emitting diodes(LEDs)remains very low due to their fundamentally limited light-extraction efficiency(LEE),calling for a novel LEE-enhancing approach to deliver a real breakthrough.Here,we propose sidewall emission-enhanced(SEE)DUV LEDs having multiple light-emitting mesa stripes to utilize inherently strong transverse-magnetic polarized light from the AlGaN active region and three-dimensional reflectors between the stripes.The SEE DUV LEDs show much enhanced light output power with a strongly upward-directed emission due to the exposed sidewall of the active region and Al-coated selective-area-grown n-type GaN micro-reflectors.The devices also show reduced operating voltage due to better n-type ohmic contact formed on the regrown n-GaN stripes when compared with conventional LEDs.Accordingly,the proposed approach simultaneously improves optical and electrical properties.In addition,strategies to further enhance the LEE up to the theoretical optimum value and control emission directionality are discussed.展开更多
We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an...We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an ultrathin p-GaN(4 nm)ohmic contact layer capable of emitting 277 nm.The experimental results show that the external quantum efficiency(EQE)and wall plug efficiency(WPE)of the structure graded from 0.75 to 0.55 in the HIL reach 5.49%and 5.04%,which are improved significantly by 182%and 209%,respectively,compared with the structure graded from 0.75 to 0.45,exhibiting a tremendous improvement.Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL,the higher the hole concentration that should be induced;thus,the DUV-LED has a higher internal quantum efficiency(IQE).Meanwhile,as the value of x decreases,the absorption of the DUV light emitted from the active region by the HIL is enhanced,reducing the light extraction efficiency(LEE).The IQE and LEE together affect the EQE performance of DUV-LEDs.To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition,the Al composition in the HIL was optimized through theoretical calculations and experiments.展开更多
ABSTRACT Embedding submicrocavities is an effective approach to improve the light out-coupling efficiency(LOCE)for planar perovskite light-emitting diodes(PeLEDs).In this work,we employ phenethylammonium iodide(PEAI)t...ABSTRACT Embedding submicrocavities is an effective approach to improve the light out-coupling efficiency(LOCE)for planar perovskite light-emitting diodes(PeLEDs).In this work,we employ phenethylammonium iodide(PEAI)to trigger the Ostwald ripening for the downward recrystallization of perovskite,resulting in spontaneous formation of buried submicrocavities as light output coupler.The simulation suggests the buried submicrocavities can improve the LOCE from 26.8 to 36.2%for near-infrared light.Therefore,PeLED yields peak external quantum efficiency(EQE)increasing from 17.3%at current density of 114 mA cm^(−2)to 25.5%at current density of 109 mA cm^(−2)and a radiance increasing from 109 to 487 W sr^(−1)m^(−2)with low rolling-off.The turn-on voltage decreased from 1.25 to 1.15 V at 0.1 W sr^(−1)m^(−2).Besides,downward recrystallization process slightly reduces the trap density from 8.90×10^(15)to 7.27×10^(15)cm^(−3).This work provides a self-assembly method to integrate buried output coupler for boosting the performance of PeLEDs.展开更多
Red plus blue light-emitting diodes(LEDs)are commonly applied in plant factories with artificial lighting due to photosynthetic pigments,which absorb strongly in red and blue light regions of the spectrum.However,plan...Red plus blue light-emitting diodes(LEDs)are commonly applied in plant factories with artificial lighting due to photosynthetic pigments,which absorb strongly in red and blue light regions of the spectrum.However,plants grown under natural environment are used to utilizing broad-wide spectrum by long-term evolution.In order to examine the effects of addition light added in red plus blue LEDs or white LEDs,green and purple leaf lettuces(Lactuca sativa L.cv.Lvdie and Ziya)were hydroponically cultivated for 20 days under white LEDs,white plus red LEDs,red plus blue LEDs,and red plus blue LEDs supplemented with ultraviolet,green or far-red light,respectively.The results indicated that the addition of far-red light in red plus blue LEDs increased leaf fresh and dry weights of green leaf lettuce by 28%and 34%,respectively.Addition of ultraviolet light did not induce any differences in growth and energy use efficiency in both lettuce cultivars,while supplementing green light with red plus blue LEDs reduced the vitamin C content of green leaf lettuce by 44%and anthocyanin content of purple leaf lettuce by 30%compared with red plus blue LEDs,respectively.Spectral absorbencies of purple leaf lettuce grown under red plus blue LEDs supplemented with green light were lower in green light region compared with those grown under red plus blue LEDs,which was associated with anthocyanin contents.White plus red LEDs significantly increased leaf fresh and dry weights of purple leaf lettuce by 25%,and no significant differences were observed in vitamin C and nitrate contents compared with white LEDs.Fresh weight,light and electrical energy use efficiencies of hydroponic green and purple leaf lettuces grown under white plus red LEDs were higher or no significant differences compared with those grown under red plus blue LEDs.In conclusion,white plus red LEDs were suggested to substitute for red plus blue LEDs in hydroponic lettuce(cv.Lvdie and Ziya)production in plant factories with artificial lighting.展开更多
Since polymer-based light-emitting diodes(PLEDs)arewellsuited building blocks for large-area and low-cost flexible display equipment,state-of-the-art thermally activated delayed fluorescence(TADF)PLEDs are in high dem...Since polymer-based light-emitting diodes(PLEDs)arewellsuited building blocks for large-area and low-cost flexible display equipment,state-of-the-art thermally activated delayed fluorescence(TADF)PLEDs are in high demand.To respond to this demand,light-emitting TADF units have initially been modified with electron-transporting units to balance the carrier transport of regiorandom TADF polymers,and simultaneously,an intramolecular sensitizing strategy has also been employed by covalently incorporating TADF sensitizers with light-emitting TADF units and hosts in conjugated polymers to accelerate the spin-flip of triplet excitons.Superior photophysical properties have been achieved by a rational regulation of the proportions of each component,achieving a photoluminescence quantumyield of 90%,an extremely high rate of reverse intersystem crossing of 3×106 s−1,and a relatively low nonradiative decay rate of around 105 s−1.As a result,the solutionprocessed PLEDs can attain an external quantum efficiency(EQE)value of 25.4%with emission peaks of around 550 nm,representing record-high performance for PLEDs.The efficiency roll-off can also be significantly suppressed,maintaining an EQE value of 24.2%at 1000 cd/m2 with ideal efficiency roll-off of lower than 5%.Encouragingly,this work provides a valid strategy to tackle the imperative need for PLEDs with high EQE and low efficiency roll-off.展开更多
Ionic thermally activated delayed fluorescence(TADF)emitters are rarely investigated due to their poor photoluminescence and electroluminescence performance.Herein,highly efficient ionic TADF emitters with charged do...Ionic thermally activated delayed fluorescence(TADF)emitters are rarely investigated due to their poor photoluminescence and electroluminescence performance.Herein,highly efficient ionic TADF emitters with charged donor–acceptor(D–A^(+))and D–A^(+)–D architectures are designed,innovatively based on the phosphonium cation electron acceptor.The symmetric D–A^(+)–D compound in doped film exhibits a high photoluminescence quantum yield of 0.91 and a short emission lifetime of 1.43 microseconds.Partially solution-processed organic lightemitting diodes based on these ionic TADF emitters achieve a maximum external quantum efficiency(EQE)of 18.3%and a peak luminance of 14,532 candelas per square meter(cd/m^(2))and show a small efficiency roll-off of 7.1%(EQE=17%)at a practical high luminance of 1000 cd/m^(2).These results demonstrate the high potential of phosphonium cations as promising electron acceptors to construct TADF emitters for high-performance electroluminescence devices.The current study opens up an appealing way for future exploitation of high-efficiency ionic TADF materials.展开更多
The importance of optical resonance in enhancing light outcoupling efficiency(OCE)is frequently overlooked in conventional bottom-emitting quantum-dot light-emitting diodes(QLEDs)due to their weak microcavity effect.H...The importance of optical resonance in enhancing light outcoupling efficiency(OCE)is frequently overlooked in conventional bottom-emitting quantum-dot light-emitting diodes(QLEDs)due to their weak microcavity effect.Herein,we show that by synergistically optimizing the optical and the electrical performances,QLEDs with efficiency approaching the theoretical limit can be realized.By introducing a high refractive index indium zinc oxide(IZO)electrode and optimizing its thickness,the light OCE is significantly improved and consequently the red QLEDs exhibit an external quantum efficiency(EQE)of 33.2%,which is 1.4-fold higher than that of the reference devices with conventional indium tin oxide(ITO)electrodes.Moreover,with a high refractive index plastic substrate and a microlens array,the EQE can further be improved to a record value of 37.5%.Similar results are obtained in green and blue devices,which show an EQE of 18.8%and 14.4%,respectively.We also predict that the theoretical EQE limit of red,green,and blue QLEDs can reach 35.4%-36.5%,24.8%-34.0%,and 25.1%-35.8%,respectively,without using any light outcoupling structures.The proposed synergistic optimization strategy enables the efficiencies of red,green,and blue QLEDs to approach their theoretical limits.展开更多
We theoretically study the light outcoupling efficiency of top-emitting organic light-emitting diode（OLED） with inverted structure and thin-film encapsulation.Thin-film optics is used to optimize the layer thickness...We theoretically study the light outcoupling efficiency of top-emitting organic light-emitting diode（OLED） with inverted structure and thin-film encapsulation.Thin-film optics is used to optimize the layer thickness to obtain high transmittance.Dipole mode is used to analyze the light outcoupling efficiency of the top-emitting OLED.Through this process,we can optimize the thin-film thickness with high transmittance and optimize the outcoupling efficiency of OLED.Compared with previous research,the current design method is a novel process.展开更多
In this paper,we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic lightemitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-op...In this paper,we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic lightemitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer.With a 24-nm out-coupling layer,the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area.By introducing an efficient electron blocking layer tris（1phenylpyrazolato,N,C2 ＇）iridium（III）（Ir（ppz） 3） to confine the exciton recombination area,the current efficiency and the colour stability of the device are effectively improved.A white emission with the Ir（ppz） 3 layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V,and the Commission Internationale de L＇Eclairage（CIE） chromaticity coordinates are almost constant during a large voltage change of 6 V-11 V.There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45,with a CIE x,y coordinate variation of only（±0.0025,±0.0008）.Even at a large viewing angle（75）,the CIE x,y coordinate change is as small as（±0.0087,±0.0013）.展开更多
We characterized the 6,12-bis{[N-（3,4-dimethylphenyl）-N-（2,4,5-trimethylphenyl）]amino} chrysene （BmPAC）, which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent devi...We characterized the 6,12-bis{[N-（3,4-dimethylphenyl）-N-（2,4,5-trimethylphenyl）]amino} chrysene （BmPAC）, which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device （WOLED） with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer （BEML） in front of the orange light emitting layer （YEML） to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light.展开更多
Comprehensive Summary Conjugated fused-ring structures have attracted extensive attention due to their high molecular rigidity to restrain excited-state relaxation and non-radiative decay,and further to enhance the lu...Comprehensive Summary Conjugated fused-ring structures have attracted extensive attention due to their high molecular rigidity to restrain excited-state relaxation and non-radiative decay,and further to enhance the luminance efficiency for emissive materials.Herein,we develop a series of donor-acceptor type thermally activated delayed fluorescence(TADF)emitters by introducing fused-ring 5H-benzofuro[3,2-c]carbazole(32BFCz)as electron donating unit.Through optimizing the numbers and structure of donor and acceptor moieties,three compounds named 32BFCzA,mCF3BFCzOXD and dCF3BFCzOXD are designed,which are composed by mono-32BFCz/trifluoromethylpicolinonitrile,penta-BFCz/3-(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene and penta-32BFCz/3,5-bis(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene as donor/acceptor groups,respectively.展开更多
We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predict...We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.展开更多
The origin of the efficiency drop of quantum dot light-emitting diode(QLED)under consecutive voltage sweeps is still a puzzle.In this work,we report the voltage sweep behavior of QLED.We observed the efficiency drop o...The origin of the efficiency drop of quantum dot light-emitting diode(QLED)under consecutive voltage sweeps is still a puzzle.In this work,we report the voltage sweep behavior of QLED.We observed the efficiency drop of red QLED with ZnMgO electron transport layer(ETL)under consecutive voltage sweeps.In contrast,the efficiency increases for ZnO ETL device.By analyzing the electrical characteristics of both devices and surface traps of ZnMgO and ZnO nanoparticles,we found the efficiency drop of ZnMgO device is related to the hole leakage mediated by trap state on ZnMgO nanoparticles.For ZnO device,the efficiency raise is due to suppressed electron leakage.The hole leakage also causes rapid lifetime degradation of ZnMgO device.However,the efficiency and lifetime degradation of ZnMgO device can be eliminated with shelf aging.Our work reveals the distinct voltage sweep behavior of QLED based on different ETLs and may help to understand the lifetime degradation mechanism in QLED.展开更多
Metal halide perovskite nanomaterials emerged as attractive emitting materials for light-emitting diodes(LEDs) devices due to their high photoluminescence quantum yield(PLQY), narrow bandwidth, high charge-carrier mob...Metal halide perovskite nanomaterials emerged as attractive emitting materials for light-emitting diodes(LEDs) devices due to their high photoluminescence quantum yield(PLQY), narrow bandwidth, high charge-carrier mobility, bandgap tunability, and facile synthesis. In the past few years, it has been witnessed an unprecedented advance in the field of metal halide perovskite nanomaterials based LEDs(Pe LEDs) with a rapid external quantum efficiency(EQE) increase from 0.1% to 14.36%. From the viewpoint of material chemistry, the chemical regulation of metal halide perovskite nanomaterials made a great contribution to the efficiency improvement of Pe LEDs. In this review, we categorize the strategies of chemical regulation as A-site cation engineering, B-site ion doping, X-site ion exchange, dimensional confinement, ligand exchange, surface passivation and interface optimization of transport layers for improving the EQEs of Pe LEDs. We also show the potentials of chemical regulation strategies to enhance the stability of Pe LEDs. Finally, we present insight toward future research directions and an outlook to further improve EQEs and stabilities of Pe LEDs aiming to practical applications.展开更多
基金supported by the National Key R & D Program of China (2016YFC0101800)National Natural Science Foundation of China (51672286, U1832159, 51772185)Science and Technology Major Project of Ningbo Municipality (2017C110028)
文摘A series of Y2.985Al5–xGaxO12:0.015Ce(YAGG:Ce,x=0,1,2,3,4,5)transparent ceramics were prepared via a solid-state reaction method.Two-step sintering technique was proved to be an effective approach to prepare functional ceramics with high Ga concentration,and Y3Ga5O12(YGG)transparent ceramic was successfully prepared for the first time.According to the variation of Al/Ga ratio,regulation of band structure and luminescence properties of YAGG:Ce transparent ceramics were effectively investigated.When Ga substitutes Al sites,the tetrahedral site is more favorable compared to the octahedral site for Ga to occupy according to the first-principle calculation.A continuous blue shift of the emission from 565 to 515 nm was achieved as Ga was gradually introduced into Y3Al5O12:Ce matrix.High quality green light was obtained by coupling the YAGG:Ce ceramics with commercial blue InGaN chips.Transparent luminescence ceramics accomplished in this work can be quite prospective for high power LED application.
基金support from the National Natural Science Foundation of China(grant nos.51925303,91833304,and 51673080)the program“JLUSTIRT”(grant no.2019TD-33).
文摘Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes(OLEDs),which adopt luminescent radicals as emitters,aiming at improving the external quantum efficiency(EQE)of OLEDs.Research on luminescent radicals and the corresponding devices is a multidisciplinary field involving organic chemistry,solid-state physics,photochemistry,electronics,and others.The relevant theories have been established step-by-step in recent years.
基金The authors gratefully acknowledge the support by the International Collaborative R&D Program of the Korea Institute for Advancement of Technology(KIAT)(M0000078,Development of Deep UV LED Technology for Industry and Medical Application)the Industrial Strategic Technology Development Program(10041878,Development of WPE 75%LED device process and standard evaluation technology)the IT R&D Program(10035598,180 lm W21 High-efficiency Nano-based LEDs)funded by the Ministry of Trade,Industry&Energy(MOTIE,Korea)。
文摘While the demand for deep ultraviolet(DUV)light sources is rapidly growing,the efficiency of current AlGaN-based DUV light-emitting diodes(LEDs)remains very low due to their fundamentally limited light-extraction efficiency(LEE),calling for a novel LEE-enhancing approach to deliver a real breakthrough.Here,we propose sidewall emission-enhanced(SEE)DUV LEDs having multiple light-emitting mesa stripes to utilize inherently strong transverse-magnetic polarized light from the AlGaN active region and three-dimensional reflectors between the stripes.The SEE DUV LEDs show much enhanced light output power with a strongly upward-directed emission due to the exposed sidewall of the active region and Al-coated selective-area-grown n-type GaN micro-reflectors.The devices also show reduced operating voltage due to better n-type ohmic contact formed on the regrown n-GaN stripes when compared with conventional LEDs.Accordingly,the proposed approach simultaneously improves optical and electrical properties.In addition,strategies to further enhance the LEE up to the theoretical optimum value and control emission directionality are discussed.
基金the National Natural Science Foundation of China(Grant No.62104085)the Innovation/Entrepreneurship Program of Jiangsu Province,China(Grant No.JSSCTD202146)。
文摘We investigate the polarization-induced doping in the gradient variation of Al composition in the pAl_(0.75)Ga_(0.25)N/Al_xGa_(1-x)N hole injection layer(HIL)for deep ultraviolet light-emitting diodes(DUV-LEDs)with an ultrathin p-GaN(4 nm)ohmic contact layer capable of emitting 277 nm.The experimental results show that the external quantum efficiency(EQE)and wall plug efficiency(WPE)of the structure graded from 0.75 to 0.55 in the HIL reach 5.49%and 5.04%,which are improved significantly by 182%and 209%,respectively,compared with the structure graded from 0.75 to 0.45,exhibiting a tremendous improvement.Both theoretical speculations and simulation results support that the larger the difference between 0.75 and x in the HIL,the higher the hole concentration that should be induced;thus,the DUV-LED has a higher internal quantum efficiency(IQE).Meanwhile,as the value of x decreases,the absorption of the DUV light emitted from the active region by the HIL is enhanced,reducing the light extraction efficiency(LEE).The IQE and LEE together affect the EQE performance of DUV-LEDs.To trade off the contradiction between the enhanced IQE and decreased LEE caused by the decrease in Al composition,the Al composition in the HIL was optimized through theoretical calculations and experiments.
基金supported by Startup Funds from the Central Organization Department and the South China University of Technology(SCUT),as well as funds from the national natural science foundation of China(Grant No:U2001217)the Guangdong Science and Technology Program(2020B121201003,2019ZT08L075,2019QN01L118,2021A1515012545)the Fundamental Research Fund for the Central Universities,SCUT(2020ZYGXZR095).
文摘ABSTRACT Embedding submicrocavities is an effective approach to improve the light out-coupling efficiency(LOCE)for planar perovskite light-emitting diodes(PeLEDs).In this work,we employ phenethylammonium iodide(PEAI)to trigger the Ostwald ripening for the downward recrystallization of perovskite,resulting in spontaneous formation of buried submicrocavities as light output coupler.The simulation suggests the buried submicrocavities can improve the LOCE from 26.8 to 36.2%for near-infrared light.Therefore,PeLED yields peak external quantum efficiency(EQE)increasing from 17.3%at current density of 114 mA cm^(−2)to 25.5%at current density of 109 mA cm^(−2)and a radiance increasing from 109 to 487 W sr^(−1)m^(−2)with low rolling-off.The turn-on voltage decreased from 1.25 to 1.15 V at 0.1 W sr^(−1)m^(−2).Besides,downward recrystallization process slightly reduces the trap density from 8.90×10^(15)to 7.27×10^(15)cm^(−3).This work provides a self-assembly method to integrate buried output coupler for boosting the performance of PeLEDs.
基金This work was supported by the National Key Research and Development Program of China(2017YFB0403901)This manuscript was presented at 2019 International Symposium on Environment Control Technology for Value-added Plant Production hold in Beijing from Aug.27-29,2019.
文摘Red plus blue light-emitting diodes(LEDs)are commonly applied in plant factories with artificial lighting due to photosynthetic pigments,which absorb strongly in red and blue light regions of the spectrum.However,plants grown under natural environment are used to utilizing broad-wide spectrum by long-term evolution.In order to examine the effects of addition light added in red plus blue LEDs or white LEDs,green and purple leaf lettuces(Lactuca sativa L.cv.Lvdie and Ziya)were hydroponically cultivated for 20 days under white LEDs,white plus red LEDs,red plus blue LEDs,and red plus blue LEDs supplemented with ultraviolet,green or far-red light,respectively.The results indicated that the addition of far-red light in red plus blue LEDs increased leaf fresh and dry weights of green leaf lettuce by 28%and 34%,respectively.Addition of ultraviolet light did not induce any differences in growth and energy use efficiency in both lettuce cultivars,while supplementing green light with red plus blue LEDs reduced the vitamin C content of green leaf lettuce by 44%and anthocyanin content of purple leaf lettuce by 30%compared with red plus blue LEDs,respectively.Spectral absorbencies of purple leaf lettuce grown under red plus blue LEDs supplemented with green light were lower in green light region compared with those grown under red plus blue LEDs,which was associated with anthocyanin contents.White plus red LEDs significantly increased leaf fresh and dry weights of purple leaf lettuce by 25%,and no significant differences were observed in vitamin C and nitrate contents compared with white LEDs.Fresh weight,light and electrical energy use efficiencies of hydroponic green and purple leaf lettuces grown under white plus red LEDs were higher or no significant differences compared with those grown under red plus blue LEDs.In conclusion,white plus red LEDs were suggested to substitute for red plus blue LEDs in hydroponic lettuce(cv.Lvdie and Ziya)production in plant factories with artificial lighting.
基金the National Natural Science Foundation of China(nos.51922021 and 52103220)the Shandong Provincial Natural Science Foundation(no.ZR2019ZD50).
文摘Since polymer-based light-emitting diodes(PLEDs)arewellsuited building blocks for large-area and low-cost flexible display equipment,state-of-the-art thermally activated delayed fluorescence(TADF)PLEDs are in high demand.To respond to this demand,light-emitting TADF units have initially been modified with electron-transporting units to balance the carrier transport of regiorandom TADF polymers,and simultaneously,an intramolecular sensitizing strategy has also been employed by covalently incorporating TADF sensitizers with light-emitting TADF units and hosts in conjugated polymers to accelerate the spin-flip of triplet excitons.Superior photophysical properties have been achieved by a rational regulation of the proportions of each component,achieving a photoluminescence quantumyield of 90%,an extremely high rate of reverse intersystem crossing of 3×106 s−1,and a relatively low nonradiative decay rate of around 105 s−1.As a result,the solutionprocessed PLEDs can attain an external quantum efficiency(EQE)value of 25.4%with emission peaks of around 550 nm,representing record-high performance for PLEDs.The efficiency roll-off can also be significantly suppressed,maintaining an EQE value of 24.2%at 1000 cd/m2 with ideal efficiency roll-off of lower than 5%.Encouragingly,this work provides a valid strategy to tackle the imperative need for PLEDs with high EQE and low efficiency roll-off.
基金This research was made possible as a result of a generous grant from the Key Research Program of Frontier Science,the Chinese Academy of Sciences(CAS)(grant no.QYZDJ-SSW-SLH033)the National Natural Science Foundation of China(grant no.52073286)+3 种基金the Natural Science Foundation of Fujian Province(grant no.2006L2005)the Fujian Science and Technology Innovation Laboratory for Optoelectronic Information of China(grant nos.2021ZR132 and 2021ZZ115)the Youth Innovation Foundation of Xiamen City(grant nos.3502Z20206082 and 3502Z20206083)the Major Research Project of Xiamen(grant no.3502Z20191015).
文摘Ionic thermally activated delayed fluorescence(TADF)emitters are rarely investigated due to their poor photoluminescence and electroluminescence performance.Herein,highly efficient ionic TADF emitters with charged donor–acceptor(D–A^(+))and D–A^(+)–D architectures are designed,innovatively based on the phosphonium cation electron acceptor.The symmetric D–A^(+)–D compound in doped film exhibits a high photoluminescence quantum yield of 0.91 and a short emission lifetime of 1.43 microseconds.Partially solution-processed organic lightemitting diodes based on these ionic TADF emitters achieve a maximum external quantum efficiency(EQE)of 18.3%and a peak luminance of 14,532 candelas per square meter(cd/m^(2))and show a small efficiency roll-off of 7.1%(EQE=17%)at a practical high luminance of 1000 cd/m^(2).These results demonstrate the high potential of phosphonium cations as promising electron acceptors to construct TADF emitters for high-performance electroluminescence devices.The current study opens up an appealing way for future exploitation of high-efficiency ionic TADF materials.
基金This work was supported by the National Natural Science Foundation of China(No.62174075)the Shenzhen Science and Technology Program(Nos.JCYJ20210324105400002 and JCYJ20220530113809022)the Guangdong University Research Program(No.2020ZDZX3062).
文摘The importance of optical resonance in enhancing light outcoupling efficiency(OCE)is frequently overlooked in conventional bottom-emitting quantum-dot light-emitting diodes(QLEDs)due to their weak microcavity effect.Herein,we show that by synergistically optimizing the optical and the electrical performances,QLEDs with efficiency approaching the theoretical limit can be realized.By introducing a high refractive index indium zinc oxide(IZO)electrode and optimizing its thickness,the light OCE is significantly improved and consequently the red QLEDs exhibit an external quantum efficiency(EQE)of 33.2%,which is 1.4-fold higher than that of the reference devices with conventional indium tin oxide(ITO)electrodes.Moreover,with a high refractive index plastic substrate and a microlens array,the EQE can further be improved to a record value of 37.5%.Similar results are obtained in green and blue devices,which show an EQE of 18.8%and 14.4%,respectively.We also predict that the theoretical EQE limit of red,green,and blue QLEDs can reach 35.4%-36.5%,24.8%-34.0%,and 25.1%-35.8%,respectively,without using any light outcoupling structures.The proposed synergistic optimization strategy enables the efficiencies of red,green,and blue QLEDs to approach their theoretical limits.
基金sponsored by the National "973" Program of China(No.2013CB328804)the National Natural Science Foundation of China(No.61307028)the Science and Technology Commission of Shanghai Municipality(No.13ZR1420000)
文摘We theoretically study the light outcoupling efficiency of top-emitting organic light-emitting diode（OLED） with inverted structure and thin-film encapsulation.Thin-film optics is used to optimize the layer thickness to obtain high transmittance.Dipole mode is used to analyze the light outcoupling efficiency of the top-emitting OLED.Through this process,we can optimize the thin-film thickness with high transmittance and optimize the outcoupling efficiency of OLED.Compared with previous research,the current design method is a novel process.
基金Project supported by the Science Fund of the Ministry of Science and Technology,China (Grant No. 2009CB930600)the National Natural Science Foundation of China (Grants Nos. 60907047,61274065,and 60977024)+4 种基金the Key Project of the Chinese Ministryof Education (Grants Nos. 104246 and 707032)the Research Fund for the Doctoral Program of Higher Education Institutions,China (Grant Nos. 20093223120003 and 20093223110003)the Natural Science Foundation of Jiangsu Province and the Higher Education Institutions of Jiangsu Province,China (Grants Nos. BK2009423,SJ209003,10KJB510013,and 11KJD510003)the Fok Ying-Tong Education Foundation,China (Grant No. 111051)the "Qing Lan" Program of Jiangsu Province and the "Pandeng"Project of Nanjing University of Posts and Telecommunications,China (Grant Nos. NY210015,NY211069,and NY210040)
文摘In this paper,we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic lightemitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer.With a 24-nm out-coupling layer,the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area.By introducing an efficient electron blocking layer tris（1phenylpyrazolato,N,C2 ＇）iridium（III）（Ir（ppz） 3） to confine the exciton recombination area,the current efficiency and the colour stability of the device are effectively improved.A white emission with the Ir（ppz） 3 layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V,and the Commission Internationale de L＇Eclairage（CIE） chromaticity coordinates are almost constant during a large voltage change of 6 V-11 V.There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45,with a CIE x,y coordinate variation of only（±0.0025,±0.0008）.Even at a large viewing angle（75）,the CIE x,y coordinate change is as small as（±0.0087,±0.0013）.
基金supported by the National Natural Science Foundation of China(Grant Nos.61136003 and 61275041)the Project of Science and TechnologyCommission of Shanghai Municipality,China(Grant No.14XD1401800)
文摘We characterized the 6,12-bis{[N-（3,4-dimethylphenyl）-N-（2,4,5-trimethylphenyl）]amino} chrysene （BmPAC）, which has been proven to be a blue fluorescent emission with high EL efficiency. The blue fluorescent device exhibits good performance with an external quantum efficiency of 5.8% and current efficiency of 8.9 cd/A, respectively. Using BmPAC, we also demonstrate a hybrid phosphorescence/fluorescence white organic light-emitting device （WOLED） with high efficiency of 36.3 cd/A. In order to improve the relative intensity of blue light, we plus a blue light-emitting layer （BEML） in front of the orange light emitting layer （YEML） to take advantage of the excess singlet excitons. With the new emitting layer of BEML/YEML/BEML, we demonstrate the fluorescence/phosphorescence/fluorescence WOLED exhibits good performance with a current efficiency of 47 cd/A and an enhanced relative intensity of blue light.
基金the National Natural Science Foundation of China(Nos.91833304 and 61761136013).
文摘Comprehensive Summary Conjugated fused-ring structures have attracted extensive attention due to their high molecular rigidity to restrain excited-state relaxation and non-radiative decay,and further to enhance the luminance efficiency for emissive materials.Herein,we develop a series of donor-acceptor type thermally activated delayed fluorescence(TADF)emitters by introducing fused-ring 5H-benzofuro[3,2-c]carbazole(32BFCz)as electron donating unit.Through optimizing the numbers and structure of donor and acceptor moieties,three compounds named 32BFCzA,mCF3BFCzOXD and dCF3BFCzOXD are designed,which are composed by mono-32BFCz/trifluoromethylpicolinonitrile,penta-BFCz/3-(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene and penta-32BFCz/3,5-bis(trifluoromethyl)phenyl)-1,3,4-oxadiazol-2-yl)benzene as donor/acceptor groups,respectively.
基金the National Natural Science Foundation of China (21290191)
文摘We introduce here a work package for a National Natural Science Foundation of China Major Project. We propose to develop computational methodology starting from the theory of electronic excitation processes to predicting the opto-electronic property for organic materials, in close collaborations with experiments. Through developing methods for the electron dynamics, considering superexchange electronic couplings, spin-orbit coupling elements between excited states, electron-phonon relaxation, intermolecular Coulomb and exchange terms we combine the statistical physics approaches including dynamic Monte Carlo, Boltzmann transport equation and Boltzmann statistics to predict the macroscopic properties of opto-electronic materials such as light-emitting efficiency, charge mobility, and exciton diffusion length. Experimental synthesis and characterization of D-A type ambipolar transport material as well as novel carbon based material will provide a test ground for the verification of theory.
基金supported by Key-Area Research and Development Program of Guangdong Province(Nos.2019B010925001 and 2019B010924001)Guangdong University Key Laboratory for Advanced Quantum Dot Displays and Lighting(No.2017KSYS007).
文摘The origin of the efficiency drop of quantum dot light-emitting diode(QLED)under consecutive voltage sweeps is still a puzzle.In this work,we report the voltage sweep behavior of QLED.We observed the efficiency drop of red QLED with ZnMgO electron transport layer(ETL)under consecutive voltage sweeps.In contrast,the efficiency increases for ZnO ETL device.By analyzing the electrical characteristics of both devices and surface traps of ZnMgO and ZnO nanoparticles,we found the efficiency drop of ZnMgO device is related to the hole leakage mediated by trap state on ZnMgO nanoparticles.For ZnO device,the efficiency raise is due to suppressed electron leakage.The hole leakage also causes rapid lifetime degradation of ZnMgO device.However,the efficiency and lifetime degradation of ZnMgO device can be eliminated with shelf aging.Our work reveals the distinct voltage sweep behavior of QLED based on different ETLs and may help to understand the lifetime degradation mechanism in QLED.
基金supported by the National Natural Science Foundation of China (51571184, 21501165)the Defense Industrial Technology Development Program (JCKY2016208B012)
文摘Metal halide perovskite nanomaterials emerged as attractive emitting materials for light-emitting diodes(LEDs) devices due to their high photoluminescence quantum yield(PLQY), narrow bandwidth, high charge-carrier mobility, bandgap tunability, and facile synthesis. In the past few years, it has been witnessed an unprecedented advance in the field of metal halide perovskite nanomaterials based LEDs(Pe LEDs) with a rapid external quantum efficiency(EQE) increase from 0.1% to 14.36%. From the viewpoint of material chemistry, the chemical regulation of metal halide perovskite nanomaterials made a great contribution to the efficiency improvement of Pe LEDs. In this review, we categorize the strategies of chemical regulation as A-site cation engineering, B-site ion doping, X-site ion exchange, dimensional confinement, ligand exchange, surface passivation and interface optimization of transport layers for improving the EQEs of Pe LEDs. We also show the potentials of chemical regulation strategies to enhance the stability of Pe LEDs. Finally, we present insight toward future research directions and an outlook to further improve EQEs and stabilities of Pe LEDs aiming to practical applications.
