An analytical model is presented to calculate the disassociation probability and the external quantum efficiency at high field in doped organic electrophosphorescence(EPH) devices. The charge recombination process and...An analytical model is presented to calculate the disassociation probability and the external quantum efficiency at high field in doped organic electrophosphorescence(EPH) devices. The charge recombination process and the triplet(T)-triplet(T) annihilation processes are taken into account in this model. The influences of applied voltage and the thickness of the device on the disassociation probability, and of current density and the thickness of the device on the external quantum efficiency are studied thoroughly by including and ignoring the disassociation of excitons. It is found that the dissociation probability of excitons will come close to 1 at high electric field, and the external EPH quantum efficiency is almost the same at low electric field. There is a large discrepancy of the external EPH quantum efficiency at high electric field for including or ignoring the disassociation of excitons.展开更多
The calculation of the external quantum efficiency(η_ ext ) of organic light-emitting devices(OLEDs) is presented theoretically. The basic idea is to obtain η_ ext by calculating the fraction of the generated light ...The calculation of the external quantum efficiency(η_ ext ) of organic light-emitting devices(OLEDs) is presented theoretically. The basic idea is to obtain η_ ext by calculating the fraction of the generated light that can escape through the top surface and the average transmittance over the escape cone. During the calculation, the effects of the interference, absorption and multiple reflections are neglected. Then a result of a typical 8-tris-hydroxyquinoline aluminum(Alq_ 3 )-based OLEDs on a planar glass substrate is obtained. And a twice increase in η_ ext can be achieved by using a high-index-glass substrate with an antireflection coating(SiO_ 2 ) on substrate surface.展开更多
The external quantum efficiency of quantum well solar cells （QWSCs） is compared with the control cells without multi-quantum wells. The QWSCs extend the absorption spectrum from 870 to 1000nm. When the wavelength is...The external quantum efficiency of quantum well solar cells （QWSCs） is compared with the control cells without multi-quantum wells. The QWSCs extend the absorption spectrum from 870 to 1000nm. When the wavelength is below 680nm,the external quantum efficiency of the QWSCs is lower than that of the control cells, but when the wavelength is above 680nm, the external quantum efficiency of the QWSCs is higher than that of the control cells. The possible reasons for this phenomenon are discussed. Basing on the experimental data,the possibility of substituting the middle cells of conventional triple-junction solar cells with the QWSCs to improve their performance is also discussed.展开更多
To investigate effective means of improving the efficiency of organic light-emitting devices （OLEDs） by making full use of ,triplet emission, a phosphorescent material Pt （II） Octaethylporphine （PtOEP） is doped ...To investigate effective means of improving the efficiency of organic light-emitting devices （OLEDs） by making full use of ,triplet emission, a phosphorescent material Pt （II） Octaethylporphine （PtOEP） is doped into polymer host polyspirobifluorene （Spiro） to allow radiative recombination of triplet excitons. The current and brightness characteristics of the devices are tested and the electroluminescent spectra are described. Both fluorescence and phosphorescence are ob- served,and an obvious increase in external quantum efficiency is realized compared to undoped devices when different phosphorescent dopant concentrations are tried. Thus,the phosphorescent emission from triplet excited states might be an effective way to increase the efficiency of OLEDs when the concentration of the phosphorescent dopant is properiy controlled.展开更多
Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well （MQW） solar cells are investigated. It is found that due to the reduction of piezoelectric polarization ...Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well （MQW） solar cells are investigated. It is found that due to the reduction of piezoelectric polarization and the enhancement of tunneling transport of photo-generated carriers in MQWs, the external quantum efficiency （EQE） of the solar cells increases in a low energy spectral range （λ 〉 370 nm） when the barrier thickness value decreases from 15 nm to 7.5 nm. But the EQE decreases abruptly when the barrier thickness value decreases down to 3.75 nm. The reasons for these experimental results are analyzed. We are aware that the reduction of depletion width in MQW region, caused by the high resistivity of the p-type GaN layer may be the main reason for the abnormally low EQE value at long wavelengths （λ 〉 370 nm）.展开更多
The realization of solution-processed tandem quantum-dot LEDs(QLEDs)remains a technical challenge due to the limitations of inefficient interconnect layer and the damage caused by multiple solution processes.Here,we d...The realization of solution-processed tandem quantum-dot LEDs(QLEDs)remains a technical challenge due to the limitations of inefficient interconnect layer and the damage caused by multiple solution processes.Here,we develop a high performance tandem QLED by face-to-face integrating a top-emitting QLED with a transparent QLED.The top and bottom units can be addressed independently,thereby enabling the tandem QLED to operate in series,parallel,and color-tunable modes for multifunctionality.In series mode,QLEDs demonstrate an ultra-low turn-on voltage of 3.3 V and a record-breaking external quantum efficiency of 60.7%.In parallel mode,QLEDs achieve an impressive brightness of over 4.8×10^(6)cdm^(-2).In color-tunable mode,the color,brightness,and color temperature can all be adjusted with a color tuning range of 114%NSTC.Moreover,both series and parallel connections contribute to an improved stability,resulting in a T95 lifetime of nearly 30,000 h at 1000 cdm^(-2),which is an improvement of approximately 2.8 times over control devices.Our work offers a feasible solution for achieving multifunctional tandem QLEDs with the advantages of solution processed,high efficiency,high brightness,long lifetime and full color tunability for various light source applications.展开更多
Solution-processed quantum dot light-emitting diodes(QLEDs)hold great potential as competitive candidates for display and lighting applications.However,the serious energy disorder between the quantum dots(QDs)and hole...Solution-processed quantum dot light-emitting diodes(QLEDs)hold great potential as competitive candidates for display and lighting applications.However,the serious energy disorder between the quantum dots(QDs)and hole transport layer(HTL)makes it challenging to achieve high-performance devices at lower voltage ranges.Here,we introduce"giant"fully alloy CdZnSe/ZnSeS core/shell QDs(size~19 nm)as the emitting layer to build high-efficient and stable QLEDs.The synthesized CdZnSe-based QDs reveal a decreased ground-state band splitting,shallow valence band maximum,and improved quasi-Fermi level splitting,which effectively flatten the energy landscape between the QD layer and hole transport layer.The higher electron concentration and accelerated hole injection significantly promote the carrier radiative recombination dynamics.Consequently,CdZnSe-based device exhibits a high power conversion efficiency(PCE)of 27.3%and an ultra-low efficiency roll-off,with a high external quantum efficiency(EQE)exceeding 25%over a wide range of low driving voltages(1.8-3.0V)and low heat generation.The record-high luminance levels of 1,400 and 8,600 cd m^(-2)are achieved at bandgap voltages of 100%and 120%,respectively.Meanwhile,These LEDs show an unprecedented operation lifetime T_(95)(time for the luminance to decrease to 95%)of 72,968 h at 1,000 cd m^(-2).Our work points to a novel path to flatten energy landscape at the QD-related interface for solution-processedphotoelectronicdevices.展开更多
Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material ...Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material than conventional CH_3NH_3-PbX_3(MAPbX_3). Herein, we fabricated a FAPbBr_3 microcrystal-based photodetector that exhibited a good responsivity of 4000 A W-1 and external quantum efficiency up to 106% under one-photon excitation, corresponding to the detectivity greater than 1014 Jones. The responsivity is two orders of magnitude higher than that of previously reported formamidinium perovskite photodetectors. Furthermore, the FAPbBr_3 photodetector's responsivity to two-photon absorption with an 800-nm excitation source can reach 0.07 A W^(-1), which is four orders of magnitude higher than that of its MAPbBr_3 counterparts. The response time of this photodetector is less than 1 ms.This study provides solid evidence that FAPbBr_3 can be an excellent candidate for highly sensitive and fast photodetectors.展开更多
Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. Howeve...Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap(1.6 e V) limits their photonharvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W^-1, a specific detectivity of 7×10^12 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of350–900 nm, with a maximum value of about 80% at 550 nm.展开更多
Cerium-doped Sr3（A11-x,Six）O4-xNxF oxynitride phosphors with different x values were synthesized by solid-state reaction. The structure and optical properties of these phosphors were investigated by X-ray diffracti...Cerium-doped Sr3（A11-x,Six）O4-xNxF oxynitride phosphors with different x values were synthesized by solid-state reaction. The structure and optical properties of these phosphors were investigated by X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and photoluminescence （PL） spectra. The XRD results showed that SiN substitution for Al-O） did not change the structure of Sr3A104F host and there was no impurity for x〈0.6. With the increasing ofx values, the absorption of phosphors at the blue region was enhanced and the emitting band varied from 519 to 529 nm under the 460 nm blue light excitation. The red shift of the emission band was associated with an increase in the crystal-field splitting and the covalence, which arose from the incorporation of N. More- over, the incorporation of N also improved the thermal quenching properties and the external quantum efficiency with a maximum value up to 43.3%, indicating that this phosphor is a promising candidate for white LEDs application.展开更多
Naturally oxidized freestanding silicon nanocrystals （Si NCs） are incorporated in commonly used encapsulating materials to explore the photoluminescent application of Si NCs in device structures such as solid-state ...Naturally oxidized freestanding silicon nanocrystals （Si NCs） are incorporated in commonly used encapsulating materials to explore the photoluminescent application of Si NCs in device structures such as solid-state lighting light-emitting diodes （LEDs） and solar cells. The quantum yield of Si NCs before the incorporation has reached about 45% at the excitation wavelength of 370 nm without any special surface modification. It is found that medium Ioadings, e.g., 5 wt% of Si NCs in encapsulating materials help to obtain high external quantum efficiency （EQE） of the mixtures of Si NCs and encapsulating materials. The curing of encapsulating materials significantly reduces EQE. Among all the encapsulating materials investigated in this work, silicone- OE6551 enables the highest EQE （21% at excitation wavelength λex = 370 nm） after curing. Based on current findings, we have discussed the continuous efforts to advance the photoluminescent application of Si NCs.展开更多
Colloidal Pb Se nanocrystals(NCs)have gained considerable attention due to their efficient carrier multiplication and emissions across near-infrared and short-wavelength infrared spectral ranges.However,the fast degra...Colloidal Pb Se nanocrystals(NCs)have gained considerable attention due to their efficient carrier multiplication and emissions across near-infrared and short-wavelength infrared spectral ranges.However,the fast degradation of colloidal Pb Se NCs in ambient conditions hampers their widespread applications in infrared optoelectronics.It is well-known that the inorganic thick-shell over core improves the stability of NCs.Here,we present the synthesis of Pb Se/Pb S core/shell NCs showing wide spectral tunability,in which the molar ratio of lead(Pb)and sulfur(S)precursors,and the concentration of sulfur and Pb Se NCs in solvent have a significant effect on the efficient Pb S shell growth.The infrared light-emitting diodes(IR-LEDs)fabricated with the Pb Se/Pb S core/shell NCs exhibit an external quantum efficiency(EQE)of 1.3%at 1280 nm.The ligand exchange to optimize the distance between NCs and chloride treatment are important processes for achieving high performance on Pb Se/Pb S NC-LEDs.Our results provide evidence for the promising potential of Pb Se/Pb S NCs over the wide range of infrared optoelectronic applications.展开更多
A new method is given to increase doping concentration of p-type ZnSe up to 1×1018 cm-3 through adding a little Te. This method gets over the difficulty of the high doping concentration of p-type ZnSe for many ye...A new method is given to increase doping concentration of p-type ZnSe up to 1×1018 cm-3 through adding a little Te. This method gets over the difficulty of the high doping concentration of p-type ZnSe for many years. The external quantum efficiency (QE) of ZnSe p-n junction solar cell has been measured, and ZnSe is a good material of the top cell in the tandem solar cells. The solar cells made from ZnSe/GaAs/Ge can cover 94% of the total solar spectrum under AM (air mass) 1.5, and their theoretical efficiency is 56%.展开更多
Vacuum-deposited perovskite light-emitting diodes(PeLEDs)have demonstrated significant potential for high-colorgamut active-matrix displays.Despite the rapid advance of green PeLEDs,red ones remain a considerable chal...Vacuum-deposited perovskite light-emitting diodes(PeLEDs)have demonstrated significant potential for high-colorgamut active-matrix displays.Despite the rapid advance of green PeLEDs,red ones remain a considerable challenge because of the inferior photophysical properties of vacuum-deposited red-light-emitting materials.Here,a rationally designed fluorine-modified phosphine oxide additive was introduced to in-situ passivate vacuum-deposited perovskites.The highly polar 2-F-TPPO incorporated perovskite films demonstrated enhanced photoluminescence quantum yield(PLQY),suppressed defects,and improved crystallinity.When implemented as active layers in PeLEDs,an external quantum efficiency(EQE)of 12.6%with an emission wavelength of 640 nm is achieved,which was 6 times higher compared to the previously reported most efficient vacuum-deposited red PeLEDs(EQE below 2%).Our findings lay the foundations for the further exploration of high-performance vacuum-deposited PeLEDs toward fullcolor perovskite displays.展开更多
Chiral phosphorescent manganese(Mn(II))complexes hold application promise in circularly polarized organic light-emitting diodes(CP-OLEDs)and three-dimensional(3D)display technologies due to their CP luminescence prope...Chiral phosphorescent manganese(Mn(II))complexes hold application promise in circularly polarized organic light-emitting diodes(CP-OLEDs)and three-dimensional(3D)display technologies due to their CP luminescence properties,but that simultaneously exhibit both high dissymmetry factors(gPL)and photoluminescence quantum yields(PLQYs)remain rare.In this study,we report planar chiral Mn(II)enantiomers,R/S-PhCyPO-MnBr_(2) and R/S-DPhPO-MnBr_(2),based on[2.2]paracyclophane phosphine oxide ligands,which demonstrate green photoluminescence with high PLQYs of 90%and 88%,and high|gPL|values of 4.2×10^(-3)and 4.0×10^(-3),respectively.Notably,the PhCyPO-MnBr_(2)-based OLED achieves a record-high maximum external quantum efficiency of 16.0% among those with Mn(II)complexes.Furthermore,CP-OLEDs incorporating these enantiomers exhibit electroluminescence peaking at 518 and 527 nm,with|gEL|factors of 4.5×10^(-3) and 4.3×10^(-3),respectively.This study provides a novel approach for the design of chiral Mn(II)complexes for high-performance CP-OLEDs.展开更多
Mini-LED backlights,combining color conversion materials with blue mini-LED chips,promise traditional liquid crystal displays(LCDs)with higher luminance,better contrast,and a wider color gamut.However,as color convers...Mini-LED backlights,combining color conversion materials with blue mini-LED chips,promise traditional liquid crystal displays(LCDs)with higher luminance,better contrast,and a wider color gamut.However,as color conversion materials,quantum dots(QDs)are toxic and unstable,whereas commercially available inorganic phosphors are too big in size to combine with small mini-LED chips and also have strong size-dependence of quantum efficiency(QE)and reliability.In this work,we prepare fine-grained Sr_(2)Si_(5)N_(8):Eu^(2+)-based red phosphors with high efficiency and stability by treating commercially available phosphors with ball milling,centrifuging,and acid washing.The particle size of phosphors can be easily controlled by milling speed,and the phosphors with a size varying from 3.5 to 0.7 mm are thus obtained.The samples remain the same QE as the original ones(~80%)even when their particle size is reduced to 3.2-3.5 mm,because they contain fewer surface suspension bond defects.More importantly,SrBaSi_(5)N_(8):Eu^(2+)phosphors show a size-independent thermal quenching behavior and a zero thermal degradation.We demonstrate that red-emitting mini-LEDs can be fabricated by combining the SrBaSi_(5)N_(8):Eu^(2+)red phosphor(3.5 mm in size)with blue mini-LED chips,which show a high external quantum efficiency(EQE)of above 31%and a super-high luminance of 34.3 Mnits.It indicates that fine and high efficiency phosphors can be obtained by the proposed method in this work,and they have great potentials for use in mini-LED displays.展开更多
Emerging quantum dots(QDs)based light-emitting field-effect transistors(QLEFETs)could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication cost...Emerging quantum dots(QDs)based light-emitting field-effect transistors(QLEFETs)could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication cost.Considerable efforts have been devoted to designing device structure and to understanding the underlying physics,yet the overall performance of QLEFETs remains low due to the charge/exciton loss at the interface and the large band offset of a QD layer with respect to the adjacent carrier transport layers.Here,we report highly efficient QLEFETs with an external quantum efficiency(EQE)of over 20%by employing a dielectric-QDs-dielectric(DQD)sandwich structure.Such DQD structure is used to control the carrier behavior by modulating energy band alignment,thus shifting the exciton recombination zone into the emissive layer.Also,enhanced radiative recombination is achieved by preventing the exciton loss due to presence of surface traps and the luminescence quenching induced by interfacial charge transfer.The DQD sandwiched design presents a new concept to improve the electroluminescence performance of QLEFETs,which can be transferred to other material systems and hence can facilitate exploitation of QDs in a new type of optoelectronic devices.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
Perovskite light-emitting diodes(PeLEDs)have shown outstanding potential in next-generation lighting and display owing to the advantages of broad spectral tunability,excellent color purity,high photoluminescence quant...Perovskite light-emitting diodes(PeLEDs)have shown outstanding potential in next-generation lighting and display owing to the advantages of broad spectral tunability,excellent color purity,high photoluminescence quantum yields(PLQYs),and low processing cost.Device efficiency and stability are crucial indicators to evaluate whether a PeLED can meet commercial application requirements.In this review,we first discuss strategies for achieving high external quantum efficiencies(EQEs),including controlling charge injection and balance,enhancing radiative recombination,and improving light outcoupling efficiency.Next,we review recent advances in operational stability of PeLEDs and emphasize the mechanisms of degradation in PeLEDs,including ion migration,structural transformations,chemical interactions,and thermal degradation.Through detailed analysis and discussion,this review aims to facilitate progress and innovation in highly efficient and stable PeLEDs,which have significant promise for display and solid-state lighting technologies,as well as other emerging applications.展开更多
Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence(CPL)characteristics.However,the further development of circularly pol...Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence(CPL)characteristics.However,the further development of circularly polarized organic light-emitting diodes(CP-OLEDs)needs to meet the requirements of high efficiency,high color purity,low cost,and high dissymmetry factor(gPLor gEL),chiral multiple resonance thermally activated delayed fluorescence(MR-TADF)materials are considered as candidates in these aspects.Herein,based on a pair of chiral spirofluorene precursors,two pairs of high-performance chiral MR-TADF emitters((R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB)are developed,which exhibit strong emissions peaking at 491 and 502 nm in toluene with full-width at half-maximum values of 25 and 33 nm,respectively.In addition,small singlet–triplet energy gaps of 0.15 and 0.10 eV with high absolute photoluminescence efficiencies of 95.0%and 96.7%are observed for p-Spiro-DtBuCzB and m-Spiro-DtBuCzB molecules,respectively.OLEDs based on p-Spiro-DtBuCzB and m-Spiro-DtBuCzB display high maximum external quantum efficiencies of 29.6%and 33.8%,respectively.Most importantly,CP-OLEDs present symmetric circularly polarized electroluminescence spectra with|gEL|factors of 3.36×10^(-4)and 7.66×10^(-4)for devices based on(R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB enantiomers,respectively.展开更多
基金Excellent Youth Foundation of Hunan Province(03JJY1008) Science Foundation for Post-doctorate of China(2004035083) National Science Foundation of Hunan Province(06JJ20034)
文摘An analytical model is presented to calculate the disassociation probability and the external quantum efficiency at high field in doped organic electrophosphorescence(EPH) devices. The charge recombination process and the triplet(T)-triplet(T) annihilation processes are taken into account in this model. The influences of applied voltage and the thickness of the device on the disassociation probability, and of current density and the thickness of the device on the external quantum efficiency are studied thoroughly by including and ignoring the disassociation of excitons. It is found that the dissociation probability of excitons will come close to 1 at high electric field, and the external EPH quantum efficiency is almost the same at low electric field. There is a large discrepancy of the external EPH quantum efficiency at high electric field for including or ignoring the disassociation of excitons.
基金National Natural Science Foundation of China(60207003 and 60376028) National"973"Project of China(2003cb314703)
文摘The calculation of the external quantum efficiency(η_ ext ) of organic light-emitting devices(OLEDs) is presented theoretically. The basic idea is to obtain η_ ext by calculating the fraction of the generated light that can escape through the top surface and the average transmittance over the escape cone. During the calculation, the effects of the interference, absorption and multiple reflections are neglected. Then a result of a typical 8-tris-hydroxyquinoline aluminum(Alq_ 3 )-based OLEDs on a planar glass substrate is obtained. And a twice increase in η_ ext can be achieved by using a high-index-glass substrate with an antireflection coating(SiO_ 2 ) on substrate surface.
基金the National High Technology Research and Development Program of China(No.2007AA05Z435)~~
文摘The external quantum efficiency of quantum well solar cells （QWSCs） is compared with the control cells without multi-quantum wells. The QWSCs extend the absorption spectrum from 870 to 1000nm. When the wavelength is below 680nm,the external quantum efficiency of the QWSCs is lower than that of the control cells, but when the wavelength is above 680nm, the external quantum efficiency of the QWSCs is higher than that of the control cells. The possible reasons for this phenomenon are discussed. Basing on the experimental data,the possibility of substituting the middle cells of conventional triple-junction solar cells with the QWSCs to improve their performance is also discussed.
文摘To investigate effective means of improving the efficiency of organic light-emitting devices （OLEDs） by making full use of ,triplet emission, a phosphorescent material Pt （II） Octaethylporphine （PtOEP） is doped into polymer host polyspirobifluorene （Spiro） to allow radiative recombination of triplet excitons. The current and brightness characteristics of the devices are tested and the electroluminescent spectra are described. Both fluorescence and phosphorescence are ob- served,and an obvious increase in external quantum efficiency is realized compared to undoped devices when different phosphorescent dopant concentrations are tried. Thus,the phosphorescent emission from triplet excited states might be an effective way to increase the efficiency of OLEDs when the concentration of the phosphorescent dopant is properiy controlled.
基金supported by the National Natural Science Fundation for Distinguished Young Scholars,China(Grant No.60925017)the National Natural Science Foundation of China(Grant Nos.61223005,10990100,and 61176126)the Tsinghua National Laboratory for Information Science and Technology Cross-Discipline Foundation,China
文摘Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well （MQW） solar cells are investigated. It is found that due to the reduction of piezoelectric polarization and the enhancement of tunneling transport of photo-generated carriers in MQWs, the external quantum efficiency （EQE） of the solar cells increases in a low energy spectral range （λ 〉 370 nm） when the barrier thickness value decreases from 15 nm to 7.5 nm. But the EQE decreases abruptly when the barrier thickness value decreases down to 3.75 nm. The reasons for these experimental results are analyzed. We are aware that the reduction of depletion width in MQW region, caused by the high resistivity of the p-type GaN layer may be the main reason for the abnormally low EQE value at long wavelengths （λ 〉 370 nm）.
基金supported by the National Key Research and Development Program of China(No.2024YFB3612400)National Natural Science Foundation of China(No.62174075)Shenzhen Science and Technology Program(Nos.JCYJ20220530113809022,JCYJ20230807093604009,and JCYJ20241202125804006).
文摘The realization of solution-processed tandem quantum-dot LEDs(QLEDs)remains a technical challenge due to the limitations of inefficient interconnect layer and the damage caused by multiple solution processes.Here,we develop a high performance tandem QLED by face-to-face integrating a top-emitting QLED with a transparent QLED.The top and bottom units can be addressed independently,thereby enabling the tandem QLED to operate in series,parallel,and color-tunable modes for multifunctionality.In series mode,QLEDs demonstrate an ultra-low turn-on voltage of 3.3 V and a record-breaking external quantum efficiency of 60.7%.In parallel mode,QLEDs achieve an impressive brightness of over 4.8×10^(6)cdm^(-2).In color-tunable mode,the color,brightness,and color temperature can all be adjusted with a color tuning range of 114%NSTC.Moreover,both series and parallel connections contribute to an improved stability,resulting in a T95 lifetime of nearly 30,000 h at 1000 cdm^(-2),which is an improvement of approximately 2.8 times over control devices.Our work offers a feasible solution for achieving multifunctional tandem QLEDs with the advantages of solution processed,high efficiency,high brightness,long lifetime and full color tunability for various light source applications.
基金funded by the National Natural Science Foundation of China(Grant Nos.22205054,U22A2072,61922028,22175056,and 22479041)Zhongyuan High-Level Talents Special Support Plan(No.244200510009)+1 种基金the National Key R&D Program of China(Grant No.2023YFE0205000)Postdoctoral Research Grant in Henan Province(No.202103041).
文摘Solution-processed quantum dot light-emitting diodes(QLEDs)hold great potential as competitive candidates for display and lighting applications.However,the serious energy disorder between the quantum dots(QDs)and hole transport layer(HTL)makes it challenging to achieve high-performance devices at lower voltage ranges.Here,we introduce"giant"fully alloy CdZnSe/ZnSeS core/shell QDs(size~19 nm)as the emitting layer to build high-efficient and stable QLEDs.The synthesized CdZnSe-based QDs reveal a decreased ground-state band splitting,shallow valence band maximum,and improved quasi-Fermi level splitting,which effectively flatten the energy landscape between the QD layer and hole transport layer.The higher electron concentration and accelerated hole injection significantly promote the carrier radiative recombination dynamics.Consequently,CdZnSe-based device exhibits a high power conversion efficiency(PCE)of 27.3%and an ultra-low efficiency roll-off,with a high external quantum efficiency(EQE)exceeding 25%over a wide range of low driving voltages(1.8-3.0V)and low heat generation.The record-high luminance levels of 1,400 and 8,600 cd m^(-2)are achieved at bandgap voltages of 100%and 120%,respectively.Meanwhile,These LEDs show an unprecedented operation lifetime T_(95)(time for the luminance to decrease to 95%)of 72,968 h at 1,000 cd m^(-2).Our work points to a novel path to flatten energy landscape at the QD-related interface for solution-processedphotoelectronicdevices.
基金the National Key R@D Program of China (Grant 2017YFA0204800)the National Natural Science Foundation of China (Grant Nos: 21533010, 21321091, 21525315, 91333116 and 21173169) for their financial supports
文摘Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material than conventional CH_3NH_3-PbX_3(MAPbX_3). Herein, we fabricated a FAPbBr_3 microcrystal-based photodetector that exhibited a good responsivity of 4000 A W-1 and external quantum efficiency up to 106% under one-photon excitation, corresponding to the detectivity greater than 1014 Jones. The responsivity is two orders of magnitude higher than that of previously reported formamidinium perovskite photodetectors. Furthermore, the FAPbBr_3 photodetector's responsivity to two-photon absorption with an 800-nm excitation source can reach 0.07 A W^(-1), which is four orders of magnitude higher than that of its MAPbBr_3 counterparts. The response time of this photodetector is less than 1 ms.This study provides solid evidence that FAPbBr_3 can be an excellent candidate for highly sensitive and fast photodetectors.
基金the International Cooperation Foundation of China (2015DFR10700)the National Natural Science Foundation of China (51403203) for the support of this researchthe support of the Russian Ministry of Education and Science state assignment (3.3197.2017/ПЧ)
文摘Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap(1.6 e V) limits their photonharvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W^-1, a specific detectivity of 7×10^12 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of350–900 nm, with a maximum value of about 80% at 550 nm.
基金Porject supported by National Basic Research Program of China(973 program,2014CB643801)National Natural Science Foundation of China(5110202151302026)
文摘Cerium-doped Sr3（A11-x,Six）O4-xNxF oxynitride phosphors with different x values were synthesized by solid-state reaction. The structure and optical properties of these phosphors were investigated by X-ray diffraction （XRD）, energy dispersive spectroscopy （EDS） and photoluminescence （PL） spectra. The XRD results showed that SiN substitution for Al-O） did not change the structure of Sr3A104F host and there was no impurity for x〈0.6. With the increasing ofx values, the absorption of phosphors at the blue region was enhanced and the emitting band varied from 519 to 529 nm under the 460 nm blue light excitation. The red shift of the emission band was associated with an increase in the crystal-field splitting and the covalence, which arose from the incorporation of N. More- over, the incorporation of N also improved the thermal quenching properties and the external quantum efficiency with a maximum value up to 43.3%, indicating that this phosphor is a promising candidate for white LEDs application.
基金supported by the National Natural Science Foundation of China(Nos.50902122 and 50832006)Partial support from R&D Program of Ministry of Education of China (No.62501040202)+2 种基金Innovation Team Project of Zhejiang Province,China(No.2009R50005)Basic Funding for Research at Zhejiang University,China(No.2011FZA4005)Major Scientific program of Zhejiang Province,China(No. 2009C01024-2)
文摘Naturally oxidized freestanding silicon nanocrystals （Si NCs） are incorporated in commonly used encapsulating materials to explore the photoluminescent application of Si NCs in device structures such as solid-state lighting light-emitting diodes （LEDs） and solar cells. The quantum yield of Si NCs before the incorporation has reached about 45% at the excitation wavelength of 370 nm without any special surface modification. It is found that medium Ioadings, e.g., 5 wt% of Si NCs in encapsulating materials help to obtain high external quantum efficiency （EQE） of the mixtures of Si NCs and encapsulating materials. The curing of encapsulating materials significantly reduces EQE. Among all the encapsulating materials investigated in this work, silicone- OE6551 enables the highest EQE （21% at excitation wavelength λex = 370 nm） after curing. Based on current findings, we have discussed the continuous efforts to advance the photoluminescent application of Si NCs.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0401702)the National Natural Science Foundation of China(Grant Nos.61674074 and 61405089)+6 种基金Development and Reform Commission of Shenzhen Project,China(Grant No.[2017]1395)Shenzhen Peacock Team Project,China(Grant No.KQTD2016030111203005)Shenzhen Key Laboratory for Advanced Quantum Dot Displays and Lighting,China(Grant No.ZDSYS201707281632549)Guangdong Province’s Key R&D Program:Micro-LED Display and Ultra-high Brightness Micro-display Technology,China(Grant No.2019B010925001)Guangdong University Key Laboratory for Advanced Quantum Dot Displays and Lighting,China(Grant No.2017KSYS007)Distinguished Young Scholar of National Natural Science Foundation of Guangdong,China(Grant No.2017B030306010)the start-up fund from Southern University of Science and Technology,Shenzhen,China
文摘Colloidal Pb Se nanocrystals(NCs)have gained considerable attention due to their efficient carrier multiplication and emissions across near-infrared and short-wavelength infrared spectral ranges.However,the fast degradation of colloidal Pb Se NCs in ambient conditions hampers their widespread applications in infrared optoelectronics.It is well-known that the inorganic thick-shell over core improves the stability of NCs.Here,we present the synthesis of Pb Se/Pb S core/shell NCs showing wide spectral tunability,in which the molar ratio of lead(Pb)and sulfur(S)precursors,and the concentration of sulfur and Pb Se NCs in solvent have a significant effect on the efficient Pb S shell growth.The infrared light-emitting diodes(IR-LEDs)fabricated with the Pb Se/Pb S core/shell NCs exhibit an external quantum efficiency(EQE)of 1.3%at 1280 nm.The ligand exchange to optimize the distance between NCs and chloride treatment are important processes for achieving high performance on Pb Se/Pb S NC-LEDs.Our results provide evidence for the promising potential of Pb Se/Pb S NCs over the wide range of infrared optoelectronic applications.
基金This work was supported by the Science Fundation of Hebei Province(No.697181)Institute of Energy Conversion,University of Delaware,USA.
文摘A new method is given to increase doping concentration of p-type ZnSe up to 1×1018 cm-3 through adding a little Te. This method gets over the difficulty of the high doping concentration of p-type ZnSe for many years. The external quantum efficiency (QE) of ZnSe p-n junction solar cell has been measured, and ZnSe is a good material of the top cell in the tandem solar cells. The solar cells made from ZnSe/GaAs/Ge can cover 94% of the total solar spectrum under AM (air mass) 1.5, and their theoretical efficiency is 56%.
基金supported by the National Natural Science Foundation of China(62322505,62425502,62374069,62375060,62375276,U23A6002,and 62104077)Shanghai Pilot Program for Basic Research(22JC1403200)+2 种基金“Pioneer”and“Leading Goose”R&D Program of Zhejiang(2024C01192)the Natural Science Foundation of Hubei Province(2024AFB423 and 2023BAB102)the National Key Research and Development Program of China(2021YFB3501800,2023YFB3608903,2024YFA1209503).
文摘Vacuum-deposited perovskite light-emitting diodes(PeLEDs)have demonstrated significant potential for high-colorgamut active-matrix displays.Despite the rapid advance of green PeLEDs,red ones remain a considerable challenge because of the inferior photophysical properties of vacuum-deposited red-light-emitting materials.Here,a rationally designed fluorine-modified phosphine oxide additive was introduced to in-situ passivate vacuum-deposited perovskites.The highly polar 2-F-TPPO incorporated perovskite films demonstrated enhanced photoluminescence quantum yield(PLQY),suppressed defects,and improved crystallinity.When implemented as active layers in PeLEDs,an external quantum efficiency(EQE)of 12.6%with an emission wavelength of 640 nm is achieved,which was 6 times higher compared to the previously reported most efficient vacuum-deposited red PeLEDs(EQE below 2%).Our findings lay the foundations for the further exploration of high-performance vacuum-deposited PeLEDs toward fullcolor perovskite displays.
基金supported by the National Natural Science Foundation of China(92256304,U23A20593)the Natural Science Foundation of Jiangsu Province(BK20243010,BK20242021)。
文摘Chiral phosphorescent manganese(Mn(II))complexes hold application promise in circularly polarized organic light-emitting diodes(CP-OLEDs)and three-dimensional(3D)display technologies due to their CP luminescence properties,but that simultaneously exhibit both high dissymmetry factors(gPL)and photoluminescence quantum yields(PLQYs)remain rare.In this study,we report planar chiral Mn(II)enantiomers,R/S-PhCyPO-MnBr_(2) and R/S-DPhPO-MnBr_(2),based on[2.2]paracyclophane phosphine oxide ligands,which demonstrate green photoluminescence with high PLQYs of 90%and 88%,and high|gPL|values of 4.2×10^(-3)and 4.0×10^(-3),respectively.Notably,the PhCyPO-MnBr_(2)-based OLED achieves a record-high maximum external quantum efficiency of 16.0% among those with Mn(II)complexes.Furthermore,CP-OLEDs incorporating these enantiomers exhibit electroluminescence peaking at 518 and 527 nm,with|gEL|factors of 4.5×10^(-3) and 4.3×10^(-3),respectively.This study provides a novel approach for the design of chiral Mn(II)complexes for high-performance CP-OLEDs.
基金This work is supported by the National Natural Science Foundation of China(Nos.51832005 and 52172157)the Fundamental Research Funds for the Central Universities(No.20720200075)Fujian Provincial Science and Technology Project(Nos.2020I0002 and 2021J01042).
文摘Mini-LED backlights,combining color conversion materials with blue mini-LED chips,promise traditional liquid crystal displays(LCDs)with higher luminance,better contrast,and a wider color gamut.However,as color conversion materials,quantum dots(QDs)are toxic and unstable,whereas commercially available inorganic phosphors are too big in size to combine with small mini-LED chips and also have strong size-dependence of quantum efficiency(QE)and reliability.In this work,we prepare fine-grained Sr_(2)Si_(5)N_(8):Eu^(2+)-based red phosphors with high efficiency and stability by treating commercially available phosphors with ball milling,centrifuging,and acid washing.The particle size of phosphors can be easily controlled by milling speed,and the phosphors with a size varying from 3.5 to 0.7 mm are thus obtained.The samples remain the same QE as the original ones(~80%)even when their particle size is reduced to 3.2-3.5 mm,because they contain fewer surface suspension bond defects.More importantly,SrBaSi_(5)N_(8):Eu^(2+)phosphors show a size-independent thermal quenching behavior and a zero thermal degradation.We demonstrate that red-emitting mini-LEDs can be fabricated by combining the SrBaSi_(5)N_(8):Eu^(2+)red phosphor(3.5 mm in size)with blue mini-LED chips,which show a high external quantum efficiency(EQE)of above 31%and a super-high luminance of 34.3 Mnits.It indicates that fine and high efficiency phosphors can be obtained by the proposed method in this work,and they have great potentials for use in mini-LED displays.
基金support from the National Natural Science Foundation of China(62174104,61735004,and 12174086)the National Key Research and Development Program of China(2016YFB0401702)the Shanghai Science and Technology Committee(19010500600)。
文摘Emerging quantum dots(QDs)based light-emitting field-effect transistors(QLEFETs)could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication cost.Considerable efforts have been devoted to designing device structure and to understanding the underlying physics,yet the overall performance of QLEFETs remains low due to the charge/exciton loss at the interface and the large band offset of a QD layer with respect to the adjacent carrier transport layers.Here,we report highly efficient QLEFETs with an external quantum efficiency(EQE)of over 20%by employing a dielectric-QDs-dielectric(DQD)sandwich structure.Such DQD structure is used to control the carrier behavior by modulating energy band alignment,thus shifting the exciton recombination zone into the emissive layer.Also,enhanced radiative recombination is achieved by preventing the exciton loss due to presence of surface traps and the luminescence quenching induced by interfacial charge transfer.The DQD sandwiched design presents a new concept to improve the electroluminescence performance of QLEFETs,which can be transferred to other material systems and hence can facilitate exploitation of QDs in a new type of optoelectronic devices.
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supported by the National Key Research and Development Program of China(No.2022YFA1204800)the Scientific Research Innovation Capability Support Project for Young Faculty(No.ZYGXQNJSKYCXNLZCXM-I25),China+1 种基金the National Natural Science Foundation of China(No.62274144)the Zhejiang Provincial Government,China.
文摘Perovskite light-emitting diodes(PeLEDs)have shown outstanding potential in next-generation lighting and display owing to the advantages of broad spectral tunability,excellent color purity,high photoluminescence quantum yields(PLQYs),and low processing cost.Device efficiency and stability are crucial indicators to evaluate whether a PeLED can meet commercial application requirements.In this review,we first discuss strategies for achieving high external quantum efficiencies(EQEs),including controlling charge injection and balance,enhancing radiative recombination,and improving light outcoupling efficiency.Next,we review recent advances in operational stability of PeLEDs and emphasize the mechanisms of degradation in PeLEDs,including ion migration,structural transformations,chemical interactions,and thermal degradation.Through detailed analysis and discussion,this review aims to facilitate progress and innovation in highly efficient and stable PeLEDs,which have significant promise for display and solid-state lighting technologies,as well as other emerging applications.
基金supported by the National Natural Science Foundation of China(92256304,U23A20593)。
文摘Chiral luminescence materials have potential applications in the field of three-dimensional displays due to their circularly polarized luminescence(CPL)characteristics.However,the further development of circularly polarized organic light-emitting diodes(CP-OLEDs)needs to meet the requirements of high efficiency,high color purity,low cost,and high dissymmetry factor(gPLor gEL),chiral multiple resonance thermally activated delayed fluorescence(MR-TADF)materials are considered as candidates in these aspects.Herein,based on a pair of chiral spirofluorene precursors,two pairs of high-performance chiral MR-TADF emitters((R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB)are developed,which exhibit strong emissions peaking at 491 and 502 nm in toluene with full-width at half-maximum values of 25 and 33 nm,respectively.In addition,small singlet–triplet energy gaps of 0.15 and 0.10 eV with high absolute photoluminescence efficiencies of 95.0%and 96.7%are observed for p-Spiro-DtBuCzB and m-Spiro-DtBuCzB molecules,respectively.OLEDs based on p-Spiro-DtBuCzB and m-Spiro-DtBuCzB display high maximum external quantum efficiencies of 29.6%and 33.8%,respectively.Most importantly,CP-OLEDs present symmetric circularly polarized electroluminescence spectra with|gEL|factors of 3.36×10^(-4)and 7.66×10^(-4)for devices based on(R/S)-p-Spiro-DtBuCzB and(R/S)-m-Spiro-DtBuCzB enantiomers,respectively.
