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
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
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
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
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
Two novel fluorene-based copolymers (PFSD and PFMD) containing squaric acid or maleimide unit in the main chain were synthesized in good yields by Suzuki coupling reaction. The resulting polymers possess excellent the...Two novel fluorene-based copolymers (PFSD and PFMD) containing squaric acid or maleimide unit in the main chain were synthesized in good yields by Suzuki coupling reaction. The resulting polymers possess excellent thermal stability, high electron affinity and high photoluminescence (PL) quantum yields. They can fluoresce in yellow-light range due to either the charge transfer between a fluorene segment and an electron-deficient containing squaric acid/maleimide segment of the polymers or the Forster energy transfer between different polymer chains. The results from PL measurements of the isothermally heated polymer thin films show that the commonly observed aggregate excimer formation in polyfluorenes is very effectively suppressed in these two polymers due to the nonlinear structures of maleimide and squaric acid moieties. Double-layer polymer light-emitting diodes (PLED) were fabricated using the resulting polymers as the emitting layers and Ba or Mg : Ag (V : V= 10 : 1) as cathodes. All the devices show bright yellow emission (562-579 nm) with different maximum external quantum efficiencies (0.006%-1.13%). Compared with the other devices, indium-tin oxide (ITO)/polyethylenedioxythiophene (PEDOT) : polystyrene sulfonic acid (PSS)PFMD/Mg : Ag has the higher maximum external quantum efficiency of 1.13% at 564 cd/m2 with a bias of 8.4 V.展开更多
b Département de Physique, Ecole Polythechnique Fédérale de Lausanne, EPFL, Lausanne, Switzerland c Department of Chemistry, Tsinghua University, Beijing 100084, China An excellent hole-transpor...b Département de Physique, Ecole Polythechnique Fédérale de Lausanne, EPFL, Lausanne, Switzerland c Department of Chemistry, Tsinghua University, Beijing 100084, China An excellent hole-transport material, 1,3-diphenyl-5-(9-phenanthryl)-2-pyrazoline (DPPhP) for OLEDs was studied. This compound not only offers high glass transition temperature (T g=96 ℃), good film forming ability, and high HOMO energy level, but also displays excellent hole-transport property. The electroluminescent device with a simple structure of ITO/DPPhP (60 nm)/AlQ (60 nm)/LiF (0.8 nm)/Al shows an external quantum efficiency as high as 1.6%.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
The optical properties ofZnO nanoparticles (NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting (DS) efficiency. Suc...The optical properties ofZnO nanoparticles (NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting (DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device (photodiode), thereby increasing its efficiency. Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency (EQE) characteristics of the final devices were measured. Through comparison of the photodiode's EQE characteristics before and after the deposition of the ZnO NPs layer, it was concluded that for the photodiode with a low UV sensitivity (about 8%), the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%, while for the photodiodes with a higher initial UV sensitivity (about 50%), the EQE in this range decreases with the ZnO layer thickness, due to the effects competing with DS, like the diminution of the ZnO layer transmittance and an increasing diffusion.展开更多
Graphene quantum dots (GQDs), have unique quantum confinement effects, tunable bandgap and luminescence property, with a wide range of potential applications such as optoelectronic and biomedical areas. However, GQDs ...Graphene quantum dots (GQDs), have unique quantum confinement effects, tunable bandgap and luminescence property, with a wide range of potential applications such as optoelectronic and biomedical areas. However, GQDs usually have a strong tendency toward aggregation especially in making solid films, which will degrade their optoelectronic properties, for example, causing undesired fluorescence quenching. Here, we designed a composite film by embedding GQDs in a polyvinyl pyrrolidone (PVP) matrix through hydrogen bonding with well-preserved fluorescence, with a small addition of acid for compensating the poor conductivity of PVP. As a multifunctional solid coating on carbon nanotube/silicon (CNT/Si) solar cells, the photon down-conversion by GQDs and the PVP anti-reflection layer for visible light lead to enhanced external quantum efficiency (by 12.34% in the ultraviolet (UV) range) and cell efficiency (up to 14.94%). Such advanced optical managing enabled by low-cost, carbon-based quantum dots, as demonstrated in our results, can be applied to more versatile optoelectronic and photovoltaic devices based on perovskites, organic and other materials.展开更多
Photomultiplication-type polymer photodetectors(PM-PPDs)were achieved with polymer P3HT as donor and PY3Se-1V as acceptor based on structure of ITO/PEDOT:PSS/active layer/Al.The optimal weight ratio of P3HT to PY3Se-1...Photomultiplication-type polymer photodetectors(PM-PPDs)were achieved with polymer P3HT as donor and PY3Se-1V as acceptor based on structure of ITO/PEDOT:PSS/active layer/Al.The optimal weight ratio of P3HT to PY3Se-1V is about 100:3.Amounts of isolated electron traps are formed with PY3Se-1V surrounded by P3HT due to rather less content of PY3Se-1V in active layers and about 0.94 e V energy offset between the lowest unoccupied molecular orbitals(LUMO)of P3HT and PY3Se-1V.The optimal PM-PPDs exhibit broad spectral response from 350 to 950 nm and external quantum efficiency(EQE)values of68,200%at 360 nm,26,400%at 630 nm and 19,500%at 850 nm under-15 V bias.The working mechanism of PM-PPDs is attributed to the interfacial trap-assisted hole tunneling injection from external circuit.The performance of PM-PPDs can be further improved by incorporating appropriate PMBBDT with high hole mobility as the third component.The EQE values of optimal ternary PM-PPDs are increased to 105,000%at 360 nm,40,000%at 630 nm and 31,800%at 850 nm under-15 V bias,benefiting from the enhanced hole transport in ternary active layers.The optimal ternary PM-PPDs were successfully applied in a light-controlled circuit to turn on or turn off light emitting diode(LED).展开更多
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Project supported by the National Natural Science Foundation of China (No. 20102004).
文摘Two novel fluorene-based copolymers (PFSD and PFMD) containing squaric acid or maleimide unit in the main chain were synthesized in good yields by Suzuki coupling reaction. The resulting polymers possess excellent thermal stability, high electron affinity and high photoluminescence (PL) quantum yields. They can fluoresce in yellow-light range due to either the charge transfer between a fluorene segment and an electron-deficient containing squaric acid/maleimide segment of the polymers or the Forster energy transfer between different polymer chains. The results from PL measurements of the isothermally heated polymer thin films show that the commonly observed aggregate excimer formation in polyfluorenes is very effectively suppressed in these two polymers due to the nonlinear structures of maleimide and squaric acid moieties. Double-layer polymer light-emitting diodes (PLED) were fabricated using the resulting polymers as the emitting layers and Ba or Mg : Ag (V : V= 10 : 1) as cathodes. All the devices show bright yellow emission (562-579 nm) with different maximum external quantum efficiencies (0.006%-1.13%). Compared with the other devices, indium-tin oxide (ITO)/polyethylenedioxythiophene (PEDOT) : polystyrene sulfonic acid (PSS)PFMD/Mg : Ag has the higher maximum external quantum efficiency of 1.13% at 564 cd/m2 with a bias of 8.4 V.
文摘b Département de Physique, Ecole Polythechnique Fédérale de Lausanne, EPFL, Lausanne, Switzerland c Department of Chemistry, Tsinghua University, Beijing 100084, China An excellent hole-transport material, 1,3-diphenyl-5-(9-phenanthryl)-2-pyrazoline (DPPhP) for OLEDs was studied. This compound not only offers high glass transition temperature (T g=96 ℃), good film forming ability, and high HOMO energy level, but also displays excellent hole-transport property. The electroluminescent device with a simple structure of ITO/DPPhP (60 nm)/AlQ (60 nm)/LiF (0.8 nm)/Al shows an external quantum efficiency as high as 1.6%.
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the financial support from the Chinese Scientific Council(CSC)
文摘The optical properties ofZnO nanoparticles (NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting (DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device (photodiode), thereby increasing its efficiency. Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency (EQE) characteristics of the final devices were measured. Through comparison of the photodiode's EQE characteristics before and after the deposition of the ZnO NPs layer, it was concluded that for the photodiode with a low UV sensitivity (about 8%), the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%, while for the photodiodes with a higher initial UV sensitivity (about 50%), the EQE in this range decreases with the ZnO layer thickness, due to the effects competing with DS, like the diminution of the ZnO layer transmittance and an increasing diffusion.
基金A.Y.C.acknowledged the support from the National Natural Science Foundation of China(NSFC)(No.51672005)the National Key R&D Program of China(No.2017YFA0206701)+1 种基金Y.Y.S.acknowledged the National Natural Science Foundation of China(NSFC)(No.51872267)X.W.Z.thanked Qihang Gong for his encouragement and support all the time.
文摘Graphene quantum dots (GQDs), have unique quantum confinement effects, tunable bandgap and luminescence property, with a wide range of potential applications such as optoelectronic and biomedical areas. However, GQDs usually have a strong tendency toward aggregation especially in making solid films, which will degrade their optoelectronic properties, for example, causing undesired fluorescence quenching. Here, we designed a composite film by embedding GQDs in a polyvinyl pyrrolidone (PVP) matrix through hydrogen bonding with well-preserved fluorescence, with a small addition of acid for compensating the poor conductivity of PVP. As a multifunctional solid coating on carbon nanotube/silicon (CNT/Si) solar cells, the photon down-conversion by GQDs and the PVP anti-reflection layer for visible light lead to enhanced external quantum efficiency (by 12.34% in the ultraviolet (UV) range) and cell efficiency (up to 14.94%). Such advanced optical managing enabled by low-cost, carbon-based quantum dots, as demonstrated in our results, can be applied to more versatile optoelectronic and photovoltaic devices based on perovskites, organic and other materials.
基金supported by the Fundamental Research Funds for the Central Universities(2021YJS176)the National Natural Science Foundation of China(61975006,62075155,62175011)+1 种基金the Postdoctoral Innovative Talent Support Program(BX20200042)the China Postdoctoral Science Foundation(2020M680327)。
文摘Photomultiplication-type polymer photodetectors(PM-PPDs)were achieved with polymer P3HT as donor and PY3Se-1V as acceptor based on structure of ITO/PEDOT:PSS/active layer/Al.The optimal weight ratio of P3HT to PY3Se-1V is about 100:3.Amounts of isolated electron traps are formed with PY3Se-1V surrounded by P3HT due to rather less content of PY3Se-1V in active layers and about 0.94 e V energy offset between the lowest unoccupied molecular orbitals(LUMO)of P3HT and PY3Se-1V.The optimal PM-PPDs exhibit broad spectral response from 350 to 950 nm and external quantum efficiency(EQE)values of68,200%at 360 nm,26,400%at 630 nm and 19,500%at 850 nm under-15 V bias.The working mechanism of PM-PPDs is attributed to the interfacial trap-assisted hole tunneling injection from external circuit.The performance of PM-PPDs can be further improved by incorporating appropriate PMBBDT with high hole mobility as the third component.The EQE values of optimal ternary PM-PPDs are increased to 105,000%at 360 nm,40,000%at 630 nm and 31,800%at 850 nm under-15 V bias,benefiting from the enhanced hole transport in ternary active layers.The optimal ternary PM-PPDs were successfully applied in a light-controlled circuit to turn on or turn off light emitting diode(LED).