利用有机磁效应研究热活化延迟荧光量子阱器件中的微观机制
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摘要
采用具有反向系间窜越(reverse intersystem crossing,RISC)特性的热活化延迟荧光(thermally activated delayed fluorescence,TADF)材料制备了量子阱有机发光二极管,测量了器件的磁电导(magneto-conductance,MC)和磁电致发光(magneto-electroluminescence,MEL),由此还可得到器件效率的磁效应(Mη),并利用这些磁效应特征曲线来研究器件中的微观过程.实验发现:室温下,尽管无量子阱参考器件的MC表现出RISC特性和载流子对三重态激子的解离机制,但量子阱器件的MC则只表现出三重态激子对载流子的散射机制;而且,无量子阱参考器件的MEL和Mη都表现出了系间窜越(ISC)和三重态激子对的湮灭(TTA)的过程,但量子阱器件的MEL则表现出ISC和三重态激子对载流子的散射机制,且其Mη只表现出了ISC属性.随着温度从室温降至20 K,量子阱器件和参考器件的ISC都增强,但量子阱器件在20 K还出现了TTA过程,而参考器件的TTA则在100 K后消失.我们提出根据量子阱器件和无量子阱器件的结构特性以及温度对F?rster能量转移和三重态激子的浓度与寿命的影响可以较好地解释这些实验现象.显然,研究量子阱器件的磁效应,不仅为发光器件提供设计思路,同时还可加深对有机磁效应的认识.
The quantum well organic light-emitting diodes(OLEDs) based on thermally activated delayed fluorescence material with reverse intersystem crossing(RISC) characteristics have been fabricated in this paper. Meanwhile, the magneto-efficiency(Mη) was obtained by measuring the magneto-conductance(MC) and magneto-electroluminescence(MEL) of the devices, and we research microscopic process of devices by analyzing the characteristic curves of magnetic field effects. Surprisingly, we found that the MC curves of nonquantum-well device showed typical RISC property and the dissociation of triplet excitons by holes at room temperature, but the MC curves merely exhibited the mechanism of electron scattering by triplet excitons in quantum well device. In addition, although the MEL and Mη curves of non-quantum well device demonstrated intersystem crossing(ISC) and triplet-triplet annihilation(TTA)process, the MEL of quantum well device showed the mechanism of electron scattering by triplet excitons and the Mη only displayed the typical ISC curves. As decreasing the temperature from 300 K to 20 K, the ISC processes of quantum or non-quantum well devices increased, however, the TTA process occurred in quantum well device at 20 K and the TTA process of non-quantum well device gradually vanished at 100 K. We propose that the structure property of quantum or non-quantum well devices, temperaturedependent F?rster energy transfer, and the lifetime and concentration of the triplet excitons can explain the experimental phenomena very well. Obviously, the research of magnetic effects in quantum well devices not only provides ideas for designing high efficient light-emitting devices, but also can deepen the understanding of organic magnetic effects.
The quantum well organic light-emitting diodes(OLEDs) based on thermally activated delayed fluorescence material with reverse intersystem crossing(RISC) characteristics have been fabricated in this paper. Meanwhile, the magneto-efficiency(Mη) was obtained by measuring the magneto-conductance(MC) and magneto-electroluminescence(MEL) of the devices, and we research microscopic process of devices by analyzing the characteristic curves of magnetic field effects. Surprisingly, we found that the MC curves of nonquantum-well device showed typical RISC property and the dissociation of triplet excitons by holes at room temperature, but the MC curves merely exhibited the mechanism of electron scattering by triplet excitons in quantum well device. In addition, although the MEL and Mη curves of non-quantum well device demonstrated intersystem crossing(ISC) and triplet-triplet annihilation(TTA)process, the MEL of quantum well device showed the mechanism of electron scattering by triplet excitons and the Mη only displayed the typical ISC curves. As decreasing the temperature from 300 K to 20 K, the ISC processes of quantum or non-quantum well devices increased, however, the TTA process occurred in quantum well device at 20 K and the TTA process of non-quantum well device gradually vanished at 100 K. We propose that the structure property of quantum or non-quantum well devices, temperaturedependent F?rster energy transfer, and the lifetime and concentration of the triplet excitons can explain the experimental phenomena very well. Obviously, the research of magnetic effects in quantum well devices not only provides ideas for designing high efficient light-emitting devices, but also can deepen the understanding of organic magnetic effects.
引文
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25 陈颖冰,袁德,向杰,等.利用有机磁电导分析Rubrene发光器件中三重态激子解离和电子散射过程.中国科学:技术科学,2016,46:61–67
26 Desai P,Shakya P,Kreouzis T,et al.Magnetoresistance and efficiency measurements of q3-based OLEDs.Phys Rev B,2007,75:094423
27 Kalinowski J,Cocchi M,Virgili D,et al.Magnetic field effects on emission and current in Alq3-based electroluminescent diodes.Chem Phys Lett,2003,380:710–715
28 Yuan D,Niu L,Chen Q,et al.The triplet-charge annihilation in copolymer-based organic light emitting diodes:Through the“Scattering Channel”or the“Dissociation Channel”?Phys Chem Chem Phys,2015,17:27609–27614
29 姜文龙,孟昭晖,丛林,等.双量子阱结构OLED效率和电流的磁效应.物理学报,2010,59:6642–6646
30 Chen P,Xiong Z,Peng Q,et al.Magneto-electroluminescence as a tool to discern the origin of delayed fluorescence:Reverse intersystem crossing or triplet-triplet annihilation?Adv Opt Mater,2014,2:142–148
31 Wagemans W,Koopmans B.Spin transport and magnetoresistance in organic semiconductors.Phys Status Solidi B,2011,248:1029–1041
32 Hu B,Wu Y.Tuning magnetoresistance between positive and negative values in organic semiconductors.Nat Mater,2007,6:985–991
33 Xiang J,Chen Y,Yuan D,et al.Abnormal temperature dependent behaviors of intersystem crossing and triplet-triplet annihilation in organic planar heterojunction devices.Appl Phys Lett,2016,109:103301
34 Hu B,Yan L,Shao M.Magnetic-field effects in organic semiconducting materials and devices.Adv Mater,2009,21:1500–1516
35 袁德,陈平,张巧明,等.激子态和电荷转移态共存的聚合物发光器件中单重态与三重态之间的自旋混合过程.科学通报,2015,60:3125–3132
36 Peng Q,Li A,Fan Y,et al.Studying the influence of triplet deactivation on the singlet-triplet inter-conversion in intra-molecular charge-transfer fluorescence-based OLEDs by magneto-electroluminescence.J Mater Chem C,2014,2:6264–6268
2 Tang C W,Van Slyke S A.Organic electroluminescent diodes.Appl Phys Lett,1987,51:913–915
3 Burroughes J H,Bradley D D C,Brown A R,et al.Erratum:Light-emitting diodes based on conjugated polymers.Nature,1990,348:352
4 Cho Y R,Cha S J,Suh M C.Ideal combination of the host and dopant materials showing thermally activated delayed fluorescent behavior.Synthetic Met,2015,209:47–54
5 Li J,Nakagawa T,Mac Donald J,et al.Highly efficient organic light-emitting diode based on a hidden thermally activated delayed fluorescence channel in a heptazine derivative.Adv Mater,2013,25:3319–3323
6 Wu S,Aonuma M,Zhang Q,et al.High-efficiency deep-blue organic light-emitting diodes based on a thermally activated delayed fluorescence emitter.J Mater Chem C,2014,2:421–424
7 Lee S Y,Yasuda T,Yang Y S,et al.Luminous butterflies:Efficient exciton harvesting by benzophenone derivatives for full-color delayed fluorescence OLEDs.Angew Chem Int Edit,2014,53:6402–6406
8 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
9 Tanaka H,Shizu K,Miyazaki H,et al.Efficient green thermally activated delayed fluorescence(TADF)from a phenoxazine-triphenyltriazine(PXZ-TRZ)derivative.Chem Commun,2012,48:11392–11394
10 Deng J,Jia W,Chen Y,et al.Guest concentration,bias current,and temperature-dependent sign inversion of magneto-electroluminescence in thermally activated delayed fluorescence devices.Sci Rep,2017,7:44396
11 Wang Q,Oswald I W H,Perez M R,et al.Doping-free organic light-emitting diodes with very high power efficiency,simple device structure,and superior spectral performance.Adv Funct Mater,2014,24:4746–4752
12 Zhao Y,Chen J,Ma D.Ultrathin nondoped emissive layers for efficient and simple monochrome and white organic light-emitting diodes.ACS Appl Mater Interf,2013,5:965–971
13 Yang X,Zhuang S,Qiao X,et al.High efficiency blue phosphorescent organic light-emitting diodes with a multiple quantum well structure for reduced efficiency roll-off.Opt Express,2012,20:24411–24417
14 Meng L,Wang H,Wei X,et al.Highly efficient nondoped organic light emitting diodes based on thermally activated delayed fluorescence emitter with quantum-well structure.ACS Appl Mater Interf,2016,8:20955–20961
15 Lei Y,Zhang Q,Chen L,et al.Ultralarge magneto-electroluminescence in exciplex-based devices driven by field-induced reverse intersystem crossing.Adv Opt Mater,2016,4:694–699
16 Wu Y,Hu B,Howe J,et al.Spin injection from ferromagnetic Co nanoclusters into organic semiconducting polymers.Phys Rev B,2007,75:075413
17 Qin W,Yin S,Gao K,et al.Investigation on organic magnetoconductance based on polaron-bipolaron transition.Appl Phys Lett,2012,100:233304
18 Lei Y L,Zhang Y,Liu R,et al.Driving current and temperature dependent magnetic-field modulated electroluminescence in Alq3-based organic light emitting diode.Org Electron,2009,10:889–894
19 Uoyama H,Goushi K,Shizu K,et al.Highly efficient organic light-emitting diodes from delayed fluorescence.Nature,2012,492:234–238
20 Delley B.From molecules to solids with the DMol3approach.J Chem Phys,2000,113:7756–7764
21 Chen P,Wang L P,Tan W Y,et al.Delayed fluorescence in a solution-processable pure red molecular organic emitter based on dithienylbenzothiadiazole:A joint optical,electroluminescence,and magnetoelectroluminescence study.ACS Appl Mater Interf,2015,7:2972–2978
22 邓军权,贾伟尧,陈颖冰,等.热活化延迟荧光器件中的发光磁效应.中国科学:物理学力学天文学,2016,46:087011
23 李晨森,任忠杰,闫寿科.热活性延迟荧光材料的设计合成及其在有机发光二极管上的应用.科学通报,2015,60:2989–3004
24 向杰,令勇洲,陈颖冰,等.器件结构对激基复合物发光磁效应的影响.中国科学:物理学力学天文学,2015,45:047002
25 陈颖冰,袁德,向杰,等.利用有机磁电导分析Rubrene发光器件中三重态激子解离和电子散射过程.中国科学:技术科学,2016,46:61–67
26 Desai P,Shakya P,Kreouzis T,et al.Magnetoresistance and efficiency measurements of q3-based OLEDs.Phys Rev B,2007,75:094423
27 Kalinowski J,Cocchi M,Virgili D,et al.Magnetic field effects on emission and current in Alq3-based electroluminescent diodes.Chem Phys Lett,2003,380:710–715
28 Yuan D,Niu L,Chen Q,et al.The triplet-charge annihilation in copolymer-based organic light emitting diodes:Through the“Scattering Channel”or the“Dissociation Channel”?Phys Chem Chem Phys,2015,17:27609–27614
29 姜文龙,孟昭晖,丛林,等.双量子阱结构OLED效率和电流的磁效应.物理学报,2010,59:6642–6646
30 Chen P,Xiong Z,Peng Q,et al.Magneto-electroluminescence as a tool to discern the origin of delayed fluorescence:Reverse intersystem crossing or triplet-triplet annihilation?Adv Opt Mater,2014,2:142–148
31 Wagemans W,Koopmans B.Spin transport and magnetoresistance in organic semiconductors.Phys Status Solidi B,2011,248:1029–1041
32 Hu B,Wu Y.Tuning magnetoresistance between positive and negative values in organic semiconductors.Nat Mater,2007,6:985–991
33 Xiang J,Chen Y,Yuan D,et al.Abnormal temperature dependent behaviors of intersystem crossing and triplet-triplet annihilation in organic planar heterojunction devices.Appl Phys Lett,2016,109:103301
34 Hu B,Yan L,Shao M.Magnetic-field effects in organic semiconducting materials and devices.Adv Mater,2009,21:1500–1516
35 袁德,陈平,张巧明,等.激子态和电荷转移态共存的聚合物发光器件中单重态与三重态之间的自旋混合过程.科学通报,2015,60:3125–3132
36 Peng Q,Li A,Fan Y,et al.Studying the influence of triplet deactivation on the singlet-triplet inter-conversion in intra-molecular charge-transfer fluorescence-based OLEDs by magneto-electroluminescence.J Mater Chem C,2014,2:6264–6268