The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage c...The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence（EL） efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.展开更多
High performance organic light-emitting devices （OLEDs） have been investigated by using fluorescent bis （2-methyl-8-quinolinolato）（para-phenylphenolato）aluminum（BAlq） as an emissive layer on the performance of...High performance organic light-emitting devices （OLEDs） have been investigated by using fluorescent bis （2-methyl-8-quinolinolato）（para-phenylphenolato）aluminum（BAlq） as an emissive layer on the performance of multicolor devices consisting of N, N＇-bis-（1-naphthyl）-N,N＇diphenyl- 1,1＇-biphenyl-4,4＇- diamine （NPB） as hole transport layer. The results show that the performance of heterostructure blue light-emitting device composed of 8-hydroxyquinoline aluminum （Alq3） as an electron transport layer has been dramatically enhanced. In the case of high performance heterostructure devices, the electroluminescent spectra has been perceived to vary strongly with the thickness of the organic layers due to the different recombination region, which indicates that various color devices composed of identical components could be implemented by changing the film thickness of different functional layers.展开更多
A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electr...A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices （OLEDs）, a sup- pression of the leak current in the current-voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide （ITO） anode etched by a conventional strong etchant of aqua regia.展开更多
We investigate the electron injection effect of inserting a thin aluminum（Al） layer into cesium carbonate（Cs2CO3）injection layer. Two groups of organic light-emitting devices（OLEDs） are fabricated. For the first...We investigate the electron injection effect of inserting a thin aluminum（Al） layer into cesium carbonate（Cs2CO3）injection layer. Two groups of organic light-emitting devices（OLEDs） are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device＇s maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.展开更多
We chose pentacene as a hole injection layer（HIL） to fabricate the high performance blue fluorescent organic lightemitting devices（OLEDs）. We found that the carrier mobility of the pentacene thin films could be ef...We chose pentacene as a hole injection layer（HIL） to fabricate the high performance blue fluorescent organic lightemitting devices（OLEDs）. We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120℃. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120℃ annealed pentacene film and n-doped electron transport layer（ETL） presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m^2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.展开更多
The development of luminescent radicals withα-type transition properties is significant for advancing the understanding of luminescence mechanisms and photophysical properties in radical-based systems.Here,we present...The development of luminescent radicals withα-type transition properties is significant for advancing the understanding of luminescence mechanisms and photophysical properties in radical-based systems.Here,we present a straightforward strategy for acquiring stable luminescent radicals withα-type transition by directly decorating bis(2,4,6-trichlorophenyl)methyl radicals(BTM)-based luminescent radicals with strong electron acceptors.This approach effectively narrows the energy gap between the singly occupied molecular orbital(SOMOα)and lowest doubly unoccupied molecular orbital(LUMOα)(ΔE_(SOMOα→LOMOα)),enabling a transform of luminescent radicals from the conventionalβ-type transition to the rareα-type transition upon D_(0)→D_(1)excitation process.Theα-type transition was experimentally validated through the fabrication of organic light-emitting diodes(OLEDs)incorporating appropriate host materials.The result also expands the selection of available host materials for OLED devices exploiting radicals as emitters,as more host materials with higher highest occupied molecular orbital(HOMO)can now be considered.This work not only establishes a rational molecular design strategy for luminescent radicals withα-type transition but also provides valuable insights to guide future research in radical-based optoelectronic materials.展开更多
Exciton(or spin)statistics is a physical principle based on the statistics of spin multiplicity.In electroluminescence,injected electrons and holes have randomized spin states,and usually form singlet or triplet excit...Exciton(or spin)statistics is a physical principle based on the statistics of spin multiplicity.In electroluminescence,injected electrons and holes have randomized spin states,and usually form singlet or triplet excitons in the ratio of 1:3.Exciton statistics determines that the upper limit of internal quantum efficiency is 25%in fluorescent devices,since only singlet exciton can decay radiatively.However,both experimental and theoretical evidence indicate that the actual efficiency can exceed the exciton statistics limit of 25%by utilizing materials with special electronic structure and optimized device structures.These results bring light to break through the exciton statistics limit and develop new-generation fluorescent materials with low cost and high efficiency.Recently,the exciton statistics,which has attracted great attention in the past decade,is being rejuvenated due to the discovery of some fluorescent materials with abnormally high efficiencies.In view of their significance in theoretical research of organic semiconductors and developing new-generation OLED materials,such materials are widely investigated in both academic institutions and industry.Several key issues still require further clarification for this kind of materials,such as the molecular design concepts.Herein,we review the progress of the materials with efficiency exceeding the exciton statistics limit,and the routes to improve exciton utilization efficiency.In the end,we present an innovative pathway to fully harvest the excitons in fluorescent devices,namely,"hot exciton"model and relevant fluorescence material with hybridized local and charge-transfer(HLCT)excited state.展开更多
A set of CH2-,NH-,and O-substituted 2,1,3-benzothiadiazole(BTD)-based derivatives have been investigated theoretically in order to explore their electronic,optical,and charge transport properties.The calculation resul...A set of CH2-,NH-,and O-substituted 2,1,3-benzothiadiazole(BTD)-based derivatives have been investigated theoretically in order to explore their electronic,optical,and charge transport properties.The calculation results show that the electronic and optical properties of the pristine molecule can be easily tuned through changing the S substituent in the central aromatic ring.Based on the calculated maximum emission wavelength,we predict that CH2-,NH-,and O-substituted BTD-based derivatives could be used as red,green,and orange light-emitting materials,respectively.After CH2-,NH-or O-substitution,the oscillator strengths of the emission spectra are enhanced with respect to that of the pristine molecule,implying that these compounds have larger fluorescence intensity.Finally,it can be deduced that CH2-,NH-,and O-substituted BTD-based derivatives may act as hole transport materials in organic light-emitting diodes.展开更多
Thermally activated delayed fuorescence(TADF)small molecule bis-[3-(9,9-dimethyl-9,10-dihydroacridine)-phenyl]-sulfone(m-ACSO2)was used as a universal host to sensitize three conventional fuorescent polymers for maxim...Thermally activated delayed fuorescence(TADF)small molecule bis-[3-(9,9-dimethyl-9,10-dihydroacridine)-phenyl]-sulfone(m-ACSO2)was used as a universal host to sensitize three conventional fuorescent polymers for maximizing the electroluminescent performance.The excitons were utilized via inter-molecular energy transfer and the non-radiative decays were successfully refrained in the condensed states.Therefore,the signifcant enhancement of the electroluminescent efciencies was demonstrated.For instance,after doping poly(9,9-dioctylfuorene-co-benzothiadiazole)(F8BT)into m-ACSO2,the external quantum efciency(EQE)was improved by a factor of 17.0 in the solution-processed organic light-emitting device(OLED),as compared with the device with neat F8BT.In terms of the other well-known fuorescent polymers,i.e.,poly(para-phenylene vinylene)copolymer(Super Yellow,SY)and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV),their EQEs in the devices were respectively enhanced by 70%and 270%,compared with the reference devices based on the conventional host 1,3-di(9H-carbazol-9-yl)benzene(mCP).Besides the improved charge balance in the bipolar TADF host,these were partially ascribed to reduced fuorescence quenching in the mixed flms.展开更多
基金Supported by the National Natural Science Foundation of China(No. 20372060), the Key National Natural Science Foundationof China(No. 20131010), the Important National Natural Science Foundation of China(No. 20490210), the"863"Program(Nos.2002AA302105 and 2002AA324080) and Foreign Communion &Cooperation of National Natural Science Foundation of China(No.20340420326).
文摘The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence（EL） efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.
基金This was work supported in part by the National Nature Science Foundation oChina under Grant No. 60425101.
文摘High performance organic light-emitting devices （OLEDs） have been investigated by using fluorescent bis （2-methyl-8-quinolinolato）（para-phenylphenolato）aluminum（BAlq） as an emissive layer on the performance of multicolor devices consisting of N, N＇-bis-（1-naphthyl）-N,N＇diphenyl- 1,1＇-biphenyl-4,4＇- diamine （NPB） as hole transport layer. The results show that the performance of heterostructure blue light-emitting device composed of 8-hydroxyquinoline aluminum （Alq3） as an electron transport layer has been dramatically enhanced. In the case of high performance heterostructure devices, the electroluminescent spectra has been perceived to vary strongly with the thickness of the organic layers due to the different recombination region, which indicates that various color devices composed of identical components could be implemented by changing the film thickness of different functional layers.
基金supported by the National Natural Science Foundation of China(Grant Nos.61307036 and 61307037)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),Chinathe University Science Research Project of Jiangsu Province,China(Grant No.12KJB510028)
文摘A controllable etching process for indium zinc oxide （IZO） films was developed by using a weak etchant of oxalic acid with a slow etching ratio. With controllable etching time and temperature, a patterned IZO electrode with smoothed surface morphology and slope edge was achieved. For the practical application in organic light emitting devices （OLEDs）, a sup- pression of the leak current in the current-voltage characteristics of OLEDs was observed. It resulted in a 1.6 times longer half lifetime in the IZO-based OLEDs compared to that using an indium tin oxide （ITO） anode etched by a conventional strong etchant of aqua regia.
基金supported by the National Natural Science Foundation of China(Grant No.60906022)the Natural Science Foundation of Tianjin,China(Grant No.10JCYBJC01100)+2 种基金the Scientific Developing Foundation of Tianjin Education Commission,China(Grant No.2011ZD02)the Key Science and Technology Support Program of Tianjin,China(Grant No.14ZCZDGX00006)the National High Technology Research and Development Program of China(Grant No.2013AA014201)
文摘We investigate the electron injection effect of inserting a thin aluminum（Al） layer into cesium carbonate（Cs2CO3）injection layer. Two groups of organic light-emitting devices（OLEDs） are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device＇s maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.
基金Project supported by the National Natural Science Foundation of China(Grant No.60906022)the Natural Science Foundation of Tianjin,China(Grant No.10JCYBJC01100)+1 种基金the Key Science and Technology Support Program of Tianjin,China(Grant No.14ZCZDGX00006)the National High Technology Research and Development Program of China(Grant No.2013AA014201)
文摘We chose pentacene as a hole injection layer（HIL） to fabricate the high performance blue fluorescent organic lightemitting devices（OLEDs）. We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120℃. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120℃ annealed pentacene film and n-doped electron transport layer（ETL） presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m^2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.
基金supported by the 2025 Jilin Province Doctoral Research Innovation Capability Enhancement Project(grant no.JJKH20250062BS)National Natural Science Foundation of China(grant no.51925303).
文摘The development of luminescent radicals withα-type transition properties is significant for advancing the understanding of luminescence mechanisms and photophysical properties in radical-based systems.Here,we present a straightforward strategy for acquiring stable luminescent radicals withα-type transition by directly decorating bis(2,4,6-trichlorophenyl)methyl radicals(BTM)-based luminescent radicals with strong electron acceptors.This approach effectively narrows the energy gap between the singly occupied molecular orbital(SOMOα)and lowest doubly unoccupied molecular orbital(LUMOα)(ΔE_(SOMOα→LOMOα)),enabling a transform of luminescent radicals from the conventionalβ-type transition to the rareα-type transition upon D_(0)→D_(1)excitation process.Theα-type transition was experimentally validated through the fabrication of organic light-emitting diodes(OLEDs)incorporating appropriate host materials.The result also expands the selection of available host materials for OLED devices exploiting radicals as emitters,as more host materials with higher highest occupied molecular orbital(HOMO)can now be considered.This work not only establishes a rational molecular design strategy for luminescent radicals withα-type transition but also provides valuable insights to guide future research in radical-based optoelectronic materials.
基金financially supported by the National Science Foundation of China(51073069,51273078)the National Basic Research Program of China(2013CB834801)
文摘Exciton(or spin)statistics is a physical principle based on the statistics of spin multiplicity.In electroluminescence,injected electrons and holes have randomized spin states,and usually form singlet or triplet excitons in the ratio of 1:3.Exciton statistics determines that the upper limit of internal quantum efficiency is 25%in fluorescent devices,since only singlet exciton can decay radiatively.However,both experimental and theoretical evidence indicate that the actual efficiency can exceed the exciton statistics limit of 25%by utilizing materials with special electronic structure and optimized device structures.These results bring light to break through the exciton statistics limit and develop new-generation fluorescent materials with low cost and high efficiency.Recently,the exciton statistics,which has attracted great attention in the past decade,is being rejuvenated due to the discovery of some fluorescent materials with abnormally high efficiencies.In view of their significance in theoretical research of organic semiconductors and developing new-generation OLED materials,such materials are widely investigated in both academic institutions and industry.Several key issues still require further clarification for this kind of materials,such as the molecular design concepts.Herein,we review the progress of the materials with efficiency exceeding the exciton statistics limit,and the routes to improve exciton utilization efficiency.In the end,we present an innovative pathway to fully harvest the excitons in fluorescent devices,namely,"hot exciton"model and relevant fluorescence material with hybridized local and charge-transfer(HLCT)excited state.
基金support from the Education Office of Jilin Province (2010142)the Institute Foundation of Siping City (2010009)supports from State Key Laboratory of Theoretical and Computational Chemistry of Jilin University
文摘A set of CH2-,NH-,and O-substituted 2,1,3-benzothiadiazole(BTD)-based derivatives have been investigated theoretically in order to explore their electronic,optical,and charge transport properties.The calculation results show that the electronic and optical properties of the pristine molecule can be easily tuned through changing the S substituent in the central aromatic ring.Based on the calculated maximum emission wavelength,we predict that CH2-,NH-,and O-substituted BTD-based derivatives could be used as red,green,and orange light-emitting materials,respectively.After CH2-,NH-or O-substitution,the oscillator strengths of the emission spectra are enhanced with respect to that of the pristine molecule,implying that these compounds have larger fluorescence intensity.Finally,it can be deduced that CH2-,NH-,and O-substituted BTD-based derivatives may act as hole transport materials in organic light-emitting diodes.
基金the fnancial support from the National Natural Science Foundation of China(Grant Nos.51873159 and 62175189)GX acknowledged the funding support from the Open Project Program of Wuhan National Laboratory for Optoelectronics(No.2019WNLOKF015).
文摘Thermally activated delayed fuorescence(TADF)small molecule bis-[3-(9,9-dimethyl-9,10-dihydroacridine)-phenyl]-sulfone(m-ACSO2)was used as a universal host to sensitize three conventional fuorescent polymers for maximizing the electroluminescent performance.The excitons were utilized via inter-molecular energy transfer and the non-radiative decays were successfully refrained in the condensed states.Therefore,the signifcant enhancement of the electroluminescent efciencies was demonstrated.For instance,after doping poly(9,9-dioctylfuorene-co-benzothiadiazole)(F8BT)into m-ACSO2,the external quantum efciency(EQE)was improved by a factor of 17.0 in the solution-processed organic light-emitting device(OLED),as compared with the device with neat F8BT.In terms of the other well-known fuorescent polymers,i.e.,poly(para-phenylene vinylene)copolymer(Super Yellow,SY)and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV),their EQEs in the devices were respectively enhanced by 70%and 270%,compared with the reference devices based on the conventional host 1,3-di(9H-carbazol-9-yl)benzene(mCP).Besides the improved charge balance in the bipolar TADF host,these were partially ascribed to reduced fuorescence quenching in the mixed flms.
