利用热致延迟荧光材料提高InP/ZnS无镉量子点发光二极管的性能
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摘要
充分利用三重态激子是提高发光器件效率的重要途径.磷光材料和热致延迟荧光材料(thermally activated delayed fluorescence, TADF)均可以实现对三重态激子的利用.然而,目前在量子点发光二极管中,采用TADF材料来实现对三重态激子的利用进而提高发光效率的工作还很少.本文采用了TADF材料4,5-二(9-咔唑基)-邻苯二腈(2CzPN)掺杂聚(9-乙烯基咔唑)(PVK)(1:5)作为空穴传输层(hole transporting layer, HTL),制备了结构为ITO/PEDOT:PSS/PVK:2CzPN/InP/ZnS QDs/ZnO/Al的量子点发光器件.结果表明, 2CzPN的引入可以提升器件的空穴传输效率,使注入的电子和空穴趋于平衡;同时,通过2CzPN中的反系间窜越过程实现了对三重态激子的利用,并通过HTL和量子点InP/ZnS之间的F?rster能量转移过程提高了InP/ZnS无镉量子点发光二极管的效率,使其最大发光亮度达到513 cd/m2.相比未掺杂控制器件的最大发光亮度(407 cd/m2),实现了26%的增长.同时,使得最大电流效率较未掺杂控制器件提高了4倍,增加到1.6 cd/A.
Cadmium-free quantum-dot light-emitting diodes(QLEDs) are the potential candidate for next generation displays due to its non-toxicity, tunable colors, saturated color emission, high luminescence efficiency, and simple fabrication process.Several methods have been proposed to improve the performance of QLEDs through synthetizing new quantum dots and charge transporting materials, optimizing the device architecture, modifying the device interfaces, and engineering the fabrication process. On the other hand, the full utilization of triplet excitons would be another important pathway to improve the efficiency of QLEDs since most triplet excitons are usually lost in fluorescence light-emitting diodes. Both the phosphorescent materials and thermally activated delayed fluorescence(TADF) materials have been proposed to realize the utilization of triplet excitons. However, in QLEDs, the use of TADF materials to achieve the use of triplet excitons to improve the luminous efficiency is still rare. Here, the TADF molecule of 2 CzPN was incorporated into PVK hole-transporting layer(HTL) with the ratio of 1:5 to achieve hybrid HTL PVK: 2 CzPN, through which QLEDs with the architecture ITO/PEDOT:PSS/PVK:2 CzPN/InP/ZnS QDs/ZnO/Al were fabricated and measured. The results show that the incorporation of 2 CzPN into PVK HTL enhances the hole transport efficiency, leading to a more balance of electrons and holes in the device. Moreover, the use of triplet excitons is achieved by the reverse intersystem crossing process in2 CzPN, and the efficiency of InP/ZnS cadmium-free QLEDs is improved by the following F?rster energy transfer process between the doped HTL and quantum dots InP/ZnS. Its maximum luminous brightness is 513 cd/m2. A 26%increase was achieved compared to the maximum luminance of the undoped control device(407 cd/m2). At the same time, the maximum current efficiency is increased by 4 times compared to the undoped control device, increasing to1.6 cd/A.
Cadmium-free quantum-dot light-emitting diodes(QLEDs) are the potential candidate for next generation displays due to its non-toxicity, tunable colors, saturated color emission, high luminescence efficiency, and simple fabrication process.Several methods have been proposed to improve the performance of QLEDs through synthetizing new quantum dots and charge transporting materials, optimizing the device architecture, modifying the device interfaces, and engineering the fabrication process. On the other hand, the full utilization of triplet excitons would be another important pathway to improve the efficiency of QLEDs since most triplet excitons are usually lost in fluorescence light-emitting diodes. Both the phosphorescent materials and thermally activated delayed fluorescence(TADF) materials have been proposed to realize the utilization of triplet excitons. However, in QLEDs, the use of TADF materials to achieve the use of triplet excitons to improve the luminous efficiency is still rare. Here, the TADF molecule of 2 CzPN was incorporated into PVK hole-transporting layer(HTL) with the ratio of 1:5 to achieve hybrid HTL PVK: 2 CzPN, through which QLEDs with the architecture ITO/PEDOT:PSS/PVK:2 CzPN/InP/ZnS QDs/ZnO/Al were fabricated and measured. The results show that the incorporation of 2 CzPN into PVK HTL enhances the hole transport efficiency, leading to a more balance of electrons and holes in the device. Moreover, the use of triplet excitons is achieved by the reverse intersystem crossing process in2 CzPN, and the efficiency of InP/ZnS cadmium-free QLEDs is improved by the following F?rster energy transfer process between the doped HTL and quantum dots InP/ZnS. Its maximum luminous brightness is 513 cd/m2. A 26%increase was achieved compared to the maximum luminance of the undoped control device(407 cd/m2). At the same time, the maximum current efficiency is increased by 4 times compared to the undoped control device, increasing to1.6 cd/A.
引文
1 Wang H C,Lin S Y,Tang A C,et al.Mesoporous silica particles integrated with all-inorganic CsPbBr3perovskite quantum-dot nanocomposites(MP-PQDs)with high stability and wide color gamut used for backlight display.Angew Chem Int Ed,2016,55:7924-7929
2 Kim H M,Kim J,Jang J.Quantum-dot light-emitting diodes with a perfluorinated ionomer-doped copper-nickel oxide hole transporting layer.Nanoscale,2018,10:7281-7290
3 Jo J H,Kim J H,Lee K H,et al.High-efficiency red electroluminescent device based on multishelled InP quantum dots.Opt Lett,2016,41:3984
4 Wu Y,Yan X,Zhang X,et al.Photovoltaic performance of a nanowire/quantum dot hybrid nanostructure array solar cell.Nanoscale Res Lett,2018,13:62
5 Chen C W,Wu D Y,Chan Y C,et al.Evaluations of the chemical stability and cytotoxicity of CuInS2and CuInS2/ZnS core/shell quantum dots.JPhys Chem C,2015,119:2852-2860
6 Ma W Q,Yang X J,Chong M,et al.Voltage tunable two-color InAs∕GaAs quantum dot infrared photodetector.Appl Phys Lett,2008,93:013502
7 Ji W,Shen H,Zhang H,et al.Over 800%efficiency enhancement of all-inorganic quantum-dot light emitting diodes with an ultrathin alumina passivating layer.Nanoscale,2018,10:11103-11109
8 Zhu B,Ji W,Duan Z,et al.Low turn-on voltage and highly bright Ag-In-Zn-S quantum dot light-emitting diodes.J Mater Chem C,2018,6:4683-4690
9 Manders J R,Qian L,Titov A,et al.High efficiency and ultra wide color gamut quantum dot LEDs for next generation displays.J Soc Inf Disp,2015,23:523-528
10 Dai X,Zhang Z,Jin Y,et al.Solution-processed,high-performance light-emitting diodes based on quantum dots.Nature,2014,515:96-99
11 Kim J H,Yang H.High-efficiency Cu-In-S quantum-dot-light-emitting device exceeding 7%.Chem Mater,2016,28:6329-6335
12 Xiang C,Koo W,Chen S,et al.Solution processed multilayer cadmium-free blue/violet emitting quantum dots light emitting diodes.Appl Phys Lett,2012,101:053303
13 Zhang Y,Xie C,Su H,et al.Employing heavy metal-free colloidal quantum dots in solution-processed white light-emitting diodes.Nano Lett,2011,11:329-332
14 Song W S,Lee S H,Yang H.Fabrication of warm,high CRI white LED using non-cadmium quantum dots.Opt Mater Express,2013,3:1468
15 Ji W,Jing P,Xu W,et al.High color purity ZnSe/ZnS core/shell quantum dot based blue light emitting diodes with an inverted device structure.Appl Phys Lett,2013,103:053106
16 Chibli H,Carlini L,Park S,et al.Cytotoxicity of InP/ZnS quantum dots related to reactive oxygen species generation.Nanoscale,2011,3:2552-2559
17 Lovingood D D,Strouse G F.Microwave induced in-situ active ion etching of growing InP nanocrystals.Nano Lett,2008,8:3394-3397
18 Xie R,Peng X.Synthesis of Cu-doped InP nanocrystals(d-dots)with ZnSe diffusion barrier as efficient and color-tunable NIR emitters.J Am Chem Soc,2009,131:10645-10651
19 Tamang S,Beaune G,Texier I,et al.Aqueous phase transfer of InP/ZnS nanocrystals conserving fluorescence and high colloidal stability.ACSNano,2011,5:9392-9402
20 Huang K,Demadrille R,Silly M G,et al.Internal structure of InP/ZnS nanocrystals unraveled by high-resolution soft X-ray Photoelectron Spectroscopy.ACS Nano,2010,4:4799-4805
21 Narayanaswamy A,Feiner L F,Meijerink A,et al.The effect of temperature and dot size on the spectral properties of colloidal InP/ZnS core-shell quantum dots.ACS Nano,2009,3:2539-2546
22 Ryu E,Kim S,Jang E,et al.Step-wise synthesis of InP/ZnS core-shell quantum dots and the role of Zinc acetate.Chem Mater,2009,21:573-575
23 Ippen C,Greco T,Wedel A.InP/ZnSe/ZnS:A novel multishell system for InP quantum dots for improved luminescence efficiency and its application in a light-emitting device.J Inf Display,2012,13:91-95
24 Wang H C,Zhang H,Chen H Y,et al.Cadmium-free InP/ZnSeS/ZnS heterostructure-based quantum dot light-emitting diodes with a ZnMgOelectron transport layer and a brightness of over 10000 cd m-2.Small,2017,13:1603962
25 Jang I,Kim J,Ippen C,et al.Inverted InP quantum dot light-emitting diodes using low-temperature solution-processed metal-oxide as an electron transport layer.Jpn J Appl Phys,2015,54:02BC01
26 Li X,Zhao Y B,Fan F,et al.Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination.Nat Photon,2018,12:159-164
27 Park Y R,Choi W K,Hong Y J.Hole barrier height reduction in inverted quantum-dot light-emitting diodes with vanadium(V)oxide/poly(N-vinylcarbazole)hole transport layer.Appl Phys Lett,2018,113:043301
28 Chen L,Chen Q,Lei Y,et al.In situ investigation of energy transfer in hybrid organic/colloidal quantum dot light-emitting diodes via magnetoelectroluminescence.Phys Chem Chem Phys,2016,18:22373-22378
29 Adachi C,Baldo M A,Thompson M E,et al.Nearly 100%internal phosphorescence efficiency in an organic light-emitting device.J Appl Phys,2001,90:5048-5051
30 Baldo M A,O?Brien D F,You Y,et al.Highly efficient phosphorescent emission from organic electroluminescent devices.Nature,1998,395:151-154
31 Zhang Y Q,Cao X A.Electroluminescence of green CdSe/ZnS quantum dots enhanced by harvesting excitons from phosphorescent molecules.Appl Phys Lett,2010,97:253115
32 Endo A,Sato K,Yoshimura K,et al.Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes.Appl Phys Lett,2011,98:083302
33 Goushi K,Yoshida K,Sato K,et al.Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion.Nat Photon,2012,6:253-258
34 Zhang D,Duan L,Li C,et al.High-efficiency fluorescent organic light-emitting devices using sensitizing hosts with a small singlet-triplet exchange energy.Adv Mater,2014,26:5050-5055
35 Nakanotani H,Higuchi T,Furukawa T,et al.High-efficiency organic light-emitting diodes with fluorescent emitters.Nat Commun,2014,5:4016
36 Chen L,Lee M H,Wang Y,et al.Interface dipole for remarkable efficiency enhancement in all-solution-processable transparent inverted quantum dot light-emitting diodes.J Mater Chem C,2018,6:2596-2603
37 Uoyama H,Goushi K,Shizu K,et al.Highly efficient organic light-emitting diodes from delayed fluorescence.Nature,2012,492:234-238
38 Lin Q,Shen H,Wang H,et al.Cadmium-free quantum dots based violet light-emitting diodes:High-efficiency and brightness via optimization of organic hole transport layers.Org Electron,2015,25:178-183
2 Kim H M,Kim J,Jang J.Quantum-dot light-emitting diodes with a perfluorinated ionomer-doped copper-nickel oxide hole transporting layer.Nanoscale,2018,10:7281-7290
3 Jo J H,Kim J H,Lee K H,et al.High-efficiency red electroluminescent device based on multishelled InP quantum dots.Opt Lett,2016,41:3984
4 Wu Y,Yan X,Zhang X,et al.Photovoltaic performance of a nanowire/quantum dot hybrid nanostructure array solar cell.Nanoscale Res Lett,2018,13:62
5 Chen C W,Wu D Y,Chan Y C,et al.Evaluations of the chemical stability and cytotoxicity of CuInS2and CuInS2/ZnS core/shell quantum dots.JPhys Chem C,2015,119:2852-2860
6 Ma W Q,Yang X J,Chong M,et al.Voltage tunable two-color InAs∕GaAs quantum dot infrared photodetector.Appl Phys Lett,2008,93:013502
7 Ji W,Shen H,Zhang H,et al.Over 800%efficiency enhancement of all-inorganic quantum-dot light emitting diodes with an ultrathin alumina passivating layer.Nanoscale,2018,10:11103-11109
8 Zhu B,Ji W,Duan Z,et al.Low turn-on voltage and highly bright Ag-In-Zn-S quantum dot light-emitting diodes.J Mater Chem C,2018,6:4683-4690
9 Manders J R,Qian L,Titov A,et al.High efficiency and ultra wide color gamut quantum dot LEDs for next generation displays.J Soc Inf Disp,2015,23:523-528
10 Dai X,Zhang Z,Jin Y,et al.Solution-processed,high-performance light-emitting diodes based on quantum dots.Nature,2014,515:96-99
11 Kim J H,Yang H.High-efficiency Cu-In-S quantum-dot-light-emitting device exceeding 7%.Chem Mater,2016,28:6329-6335
12 Xiang C,Koo W,Chen S,et al.Solution processed multilayer cadmium-free blue/violet emitting quantum dots light emitting diodes.Appl Phys Lett,2012,101:053303
13 Zhang Y,Xie C,Su H,et al.Employing heavy metal-free colloidal quantum dots in solution-processed white light-emitting diodes.Nano Lett,2011,11:329-332
14 Song W S,Lee S H,Yang H.Fabrication of warm,high CRI white LED using non-cadmium quantum dots.Opt Mater Express,2013,3:1468
15 Ji W,Jing P,Xu W,et al.High color purity ZnSe/ZnS core/shell quantum dot based blue light emitting diodes with an inverted device structure.Appl Phys Lett,2013,103:053106
16 Chibli H,Carlini L,Park S,et al.Cytotoxicity of InP/ZnS quantum dots related to reactive oxygen species generation.Nanoscale,2011,3:2552-2559
17 Lovingood D D,Strouse G F.Microwave induced in-situ active ion etching of growing InP nanocrystals.Nano Lett,2008,8:3394-3397
18 Xie R,Peng X.Synthesis of Cu-doped InP nanocrystals(d-dots)with ZnSe diffusion barrier as efficient and color-tunable NIR emitters.J Am Chem Soc,2009,131:10645-10651
19 Tamang S,Beaune G,Texier I,et al.Aqueous phase transfer of InP/ZnS nanocrystals conserving fluorescence and high colloidal stability.ACSNano,2011,5:9392-9402
20 Huang K,Demadrille R,Silly M G,et al.Internal structure of InP/ZnS nanocrystals unraveled by high-resolution soft X-ray Photoelectron Spectroscopy.ACS Nano,2010,4:4799-4805
21 Narayanaswamy A,Feiner L F,Meijerink A,et al.The effect of temperature and dot size on the spectral properties of colloidal InP/ZnS core-shell quantum dots.ACS Nano,2009,3:2539-2546
22 Ryu E,Kim S,Jang E,et al.Step-wise synthesis of InP/ZnS core-shell quantum dots and the role of Zinc acetate.Chem Mater,2009,21:573-575
23 Ippen C,Greco T,Wedel A.InP/ZnSe/ZnS:A novel multishell system for InP quantum dots for improved luminescence efficiency and its application in a light-emitting device.J Inf Display,2012,13:91-95
24 Wang H C,Zhang H,Chen H Y,et al.Cadmium-free InP/ZnSeS/ZnS heterostructure-based quantum dot light-emitting diodes with a ZnMgOelectron transport layer and a brightness of over 10000 cd m-2.Small,2017,13:1603962
25 Jang I,Kim J,Ippen C,et al.Inverted InP quantum dot light-emitting diodes using low-temperature solution-processed metal-oxide as an electron transport layer.Jpn J Appl Phys,2015,54:02BC01
26 Li X,Zhao Y B,Fan F,et al.Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination.Nat Photon,2018,12:159-164
27 Park Y R,Choi W K,Hong Y J.Hole barrier height reduction in inverted quantum-dot light-emitting diodes with vanadium(V)oxide/poly(N-vinylcarbazole)hole transport layer.Appl Phys Lett,2018,113:043301
28 Chen L,Chen Q,Lei Y,et al.In situ investigation of energy transfer in hybrid organic/colloidal quantum dot light-emitting diodes via magnetoelectroluminescence.Phys Chem Chem Phys,2016,18:22373-22378
29 Adachi C,Baldo M A,Thompson M E,et al.Nearly 100%internal phosphorescence efficiency in an organic light-emitting device.J Appl Phys,2001,90:5048-5051
30 Baldo M A,O?Brien D F,You Y,et al.Highly efficient phosphorescent emission from organic electroluminescent devices.Nature,1998,395:151-154
31 Zhang Y Q,Cao X A.Electroluminescence of green CdSe/ZnS quantum dots enhanced by harvesting excitons from phosphorescent molecules.Appl Phys Lett,2010,97:253115
32 Endo A,Sato K,Yoshimura K,et al.Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes.Appl Phys Lett,2011,98:083302
33 Goushi K,Yoshida K,Sato K,et al.Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion.Nat Photon,2012,6:253-258
34 Zhang D,Duan L,Li C,et al.High-efficiency fluorescent organic light-emitting devices using sensitizing hosts with a small singlet-triplet exchange energy.Adv Mater,2014,26:5050-5055
35 Nakanotani H,Higuchi T,Furukawa T,et al.High-efficiency organic light-emitting diodes with fluorescent emitters.Nat Commun,2014,5:4016
36 Chen L,Lee M H,Wang Y,et al.Interface dipole for remarkable efficiency enhancement in all-solution-processable transparent inverted quantum dot light-emitting diodes.J Mater Chem C,2018,6:2596-2603
37 Uoyama H,Goushi K,Shizu K,et al.Highly efficient organic light-emitting diodes from delayed fluorescence.Nature,2012,492:234-238
38 Lin Q,Shen H,Wang H,et al.Cadmium-free quantum dots based violet light-emitting diodes:High-efficiency and brightness via optimization of organic hole transport layers.Org Electron,2015,25:178-183