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三线态激子-电荷相互作用(triplet excition-charge interaction, TQI)有解离和散射两种形式, 但至今仍未明确空穴注入层如何影响三线态激子的解离和散射以及磁电导(magneto-conductance, MC)正负之间的转变. 本文采用能产生载流子阶梯效应的HAT-CN作为空穴注入层, 运用磁效应作为工具对器件内部微观机理进行研究. 结果表明, 器件内部存在超精细、解离、散射三个特征磁场, 利用Lorentzian和non-Lorentzian函数对MC进行拟合并得以验证. 超精细场源于载流子自旋与氢核自旋间的超精细相互作用. 随磁场增强, 空穴注入层与空穴传输层界面产生载流子阶梯效应, 提高了空穴注入效率, 三线态激子被空穴解离后产生二次载流子. 载流子阶梯效应也会导致注入电荷大量积累, 载流子被三线态激子散射, 使其迁移率降低, 不利于激发态的形成和器件发光. MC由
$ {K_{\text{S}}}/{K_{\text{T}}} $ (重组速率比)调制, 电压较小时$ {K_{\text{S}}} \gg {K_{\text{T}}} $ , 重组比相对较大, 产生正MC; 随电压增大$ {K_{\text{S}}} \approx {K_{\text{T}}} = K $ , 此时$ {K_{\text{S}}}/{K_{\text{T}}} $ 趋近于1, 出现负MC; 尤其在低温下, MC均为负值. 本工作为空穴注入层调控三线态激子的解离和散射及MC正负之间的转变提供新思路.Triplet exciton-charge interaction (TQI) has two forms: dissociation and scattering, However, it is still unclear how the hole injection layer affects the dissociation and scattering of triplet excition and the transition between positive and negative values of magneto-conductance (MC). In this paper, HAT-CN, which can produce carrier ladder effect, is used as hole injection layer (HIL), and magnetic effect is used as a tool to study it. The results show that there are three characteristic magnetic fields in the device: hyperfine, dissociation and scattering, which are verified by fitting the MC with Lorentzian and non-Lorentzian functions. The hyperfine characteristic magnetic field results from the magnetic field suppressing superfine field-induced charge-spin mixing. With the enhancement of magnetic field, hole injection layer/hole transport layer interface produces carrier ladder effect, which improves the hole injection efficiency. The triplet excitions are separated by the hole, then the secondary carriers are produced, which makes the device’s luminous brightness and efficiency reach to 43210 cd/m2 and 9.8 cd/A, respectively. The carrier ladder effect will also lead to a large accumulation of injected charges, resulting in the scattering of charge carriers by triplet excition, thereby reducing their mobility, which is not conducive to the formation of excited states nor device luminescence. The MC is modulated by KS/KT (recombination rate ratio), and when the electric field is small$ {K}_{{\rm{S}}}\gg {K}_{{\rm{T}}} $ , the recombination ratio is relatively large, resulting in positive MC. With the increase of electric field$ {K}_{{\rm{S}}}\approx {K}_{{\rm{T}}}=K$ , KS/KT approaches 1 at this time, resulting in an MC, which is negative in a low temperature environment. This work provides a novel approach for regulating and effectively utilizing triplet excitons.-
Keywords:
- HAT-CN /
- organic light-emitting diode /
- hole injection layer /
- magnetic conductivity
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图 1 (a) MoO3, PEDOT:PSS, HAT-CN, NPB分子结构; (b) 器件1—4的归一化电致发光谱图, 插图为发光峰局部放大图; (c) 器件4的器件结构图能级及电荷产生原理图; (d)器件1—4的亮度-电压曲线; (e)器件1—4的电流效率-电流密度曲线; (f) 器件4的界面ITO/HAT-CN/NPB能级排列图[4]
Fig. 1. (a) Molecular structure of MoO3, PEDOT:PSS, HAT-CN, NPB; (b) normalized EL spectra of devices 1–4, illustrated as local magnification of luminous peaks; (c) device structure diagram and charge generation schematic diagram of device 4; (d) luminance-voltage curves of devices 1–4; (e) current efficiency-current density curves of devices 1–4; (f) ITO/HAT-CN/NPB energy level arrangement diagram at the interface of device 4 [4].
图 2 常温时器件4 的磁效应 (a) 3—5 V时的MC(蓝色系曲线), MEL(绿色系曲线); (b) 3 V时0 mT < |B| < 50 mT范围内MC曲线; (c) 电流密度-电压线性拟合曲线; (d) 内部微观机制反应原理; 其中TF(LT)表示低温条件时发生三线态-三线态激子湮灭过程; q为电荷; ∆E为能极差; S0为基态; 1PP和3PP分别为单线态极化子和三线态极化子; kcoll为三线态激子和电荷相遇的速率常数; kscat, kdiss, kquen分别为散射通道、解离通道和淬灭通道的速率常数.
Fig. 2. Magneto-effect of device 4 at room temperature: (a) MC (blue curve) and MEL (green curve) at 3–5 V; (b) the MC curve within the scope of 0 mT < |B| < 50 mT at 3 V; (c) linear fitting curve of current density-voltage; (d) reaction principle of internal microscopic mechanism. TF(LT) represents the triplet-triplet exciton annihilation process at low temperature. q is the charge. ∆E is the energy range. S0 is the ground state. 1PP and 3PP are singlet polaron and triplet polaron respectively. kcoll is the rate constant at which triplet exciton and charge meet. kscat, kdiss and kquen are the rate constants of scattering channel, dissociation channel and quenching channel, respectively.
图 3 (a)—(d) 器件1—4在偏置电压为6 V时的MC实验曲线及拟合曲线; (a)—(c) 插图分别为器件1—3的结构及能级图
Fig. 3. MC experimental curves and fitting curves of (a)–(d) devices 1–4 when the bias voltage is 6 V; (a)–(c) illustrations are the structure and energy level diagrams of devices 1–3 respectively.
图 4 在300, 195, 95 K下, (a)—(c) 注入电流强度分为400, 600, 800 μA时器件4的MC曲线; (d) 电流-电压曲线, 插图为亮度-电压曲线
Fig. 4. (a)–(c) MC curves of device 4 at 300, 195, 95 K with current of 400, 600, 800 μA; (d) current-voltage curves, where the inset shows the lightness-voltage curve.
图 5 (a)—(d) HAT-CN厚度为5—20 nm时, 电压为3, 4, 5, 6 V下的MC图; (e) 磁场为200 mT时, 不同偏压下的MC曲线; (f) 4类器件的效率比较图
Fig. 5. (a)–(d) MC diagram with the voltage of 3, 4, 5, 6 V when the thickness of HAT-CN is 5—20 nm; (e) MC curves with a magnetic field of 200 mT and different bias voltages; (f) efficiency comparison diagram of four types of devices.
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[1] Yuan J K, Dai Y F, Sun Q, Qiao X F, Yang D Z, Chen J S, Ma D G 2019 Semicond. Sci. Technol. 34 105010
Google Scholar
[2] Chang Q, Lü Z Y, Yin Y H, Xiao J, Wang J L 2022 Displays 75 102306
Google Scholar
[3] Oh E, Park S, Jeong J, Kang J S, Lee H, Yi Y 2017 Chem. Phys. 668 64
[4] Liu Z Y, Wei P C, Bin Z Y, Wang X W, Zhang D D, Duan L 2021 Sci. China Mater. 64 3124
Google Scholar
[5] Park H G, Park S G 2019 Coatings 9 648
Google Scholar
[6] Chen Y B, Jia W Y, Xiang J, Yuan D, Chen Q S, Chen L X, Xiong Z H 2016 Org. Electron. 39 207
[7] Hu B, Yue W 2003 Nat. Mater. 6 985
Google Scholar
[8] Desai P , Shakya P , Kreouzis T, Gillin W P, Morley N A, Gibbs M R J 2007 Phys. Rev. B 75 094423
Google Scholar
[9] Shao M, Yan L , Li M X, Llia I, Hu B 2013 J. Mater. Chem. C 1 1330
Google Scholar
[10] Park C H, Kang S W, Jung S G, Lee J D, Park Y W, Ju B K 2021 Sci. Rep. 11 3430
Google Scholar
[11] Wu F J, Zhao X, Zhu H Q, Tang X T, Ning Y R, Chen J, Chen X L, Xiong Z H 2022 ACS Photonics 9 2713
Google Scholar
[12] Mischok A, Hillebrandt S, Kwon S, Cather M C 2023 Nat. Photonics 17 393
Google Scholar
[13] Niu L B, Zhong Y, Chen L J, Zhang Q M, Guan Y X 2020 Org. Electron. 87 105971
Google Scholar
[14] 王辉耀, 宁亚茹, 吴凤娇, 赵茜, 陈敬, 朱洪强, 魏福贤, 吴雨廷, 熊祖洪 2022 物理学报 71 217201
Google Scholar
Wang H Y, Ning Y R, Wu F J, Zhao Q, Chen J, Zhu H Q, Wei F X, Wu Y T, Xiong Z H 2022 Acta Phys. Sin. 71 217201
Google Scholar
[15] Huh J S, Sung M J, Kwon S K, Kim Y H, Kim J J 2021 Adv. Funct. Mater. 31 2100967
Google Scholar
[16] Deng Z B, Lee S T, Webb D P, Chan Y C, Gambling W A 1999 Synth. Met. 107 107
Google Scholar
[17] Kepler R G, Beeson P M, Jacobs S J, Anderson R A, Sinclair M B, Valencia V S, Cahill P A 1995 Appl. Phys. Lett. 66 3618
Google Scholar
[18] Chen B J, Lai W Y, Gao Z Q, Lee C S, Lee S T, Gambling W A 1999 Appl. Phys. Lett. 75 4010
Google Scholar
[19] Lee H, Cho S W, Yi Y 2016 Curr. Appl. Phys. 16 1533
Google Scholar
[20] Ding L, Sun Y Q, Chen H, Zu F S, Wang Z K, Liao L S 2014 J. Mater. Chem. C 2 10403
Google Scholar
[21] Weng Z C, Gillin W P, Kreouzis T 2019 Sci. Rep. 9 3439
Google Scholar
[22] Van Eersel, H, Bobbert P S, Janssen R A J, Coehoorn R 2016 J. Appl. Phys. 119 163102
Google Scholar
[23] Hu B, Yan L, Shao M 2009 Adv. Mater. 21 1500
[24] Bi H, Huo C Y, Song X X, Li Z Q, Tang H N, Griesse-Nascimento S, Huang K C, Cheng J X, Nienhaus L, Bawendi M G, Lin H Y G, Wang Y, Saikin S K 2020 J. Phys. Chem. Lett. 11 9364
Google Scholar
[25] Hayashi H, Sakaguchi Y, Wakasa M 2001 Bull. Chem. Soc. Jpn. 74 773
Google Scholar
[26] Kersten S P, Schellekens A J, Koopmans B, Bobbert P A 2011 Phys. Rev. Lett. 106 197402
Google Scholar
[27] Jia W Y, Zhang Q M, Chen L J, Ling Y Z, Liu H, Lu C L, Chen P, Xiong Z H 2015 Org. Electron. 22 210
Google Scholar
[28] Mark P, Helfrich W 1962 J. Appl. Phys. 33 205
Google Scholar
[29] Wohlgenannt M, Vardeny Z V 2003 J. Phys-condens. Mat. 15 R83
Google Scholar
[30] Gärditz C, Mückl A G, Cölle M 2005 J. Appl. Phys. 98 104507
Google Scholar
[31] Tang X T, Hu Y Q, Jia W Y, Pan R H, Deng J Q, He Z H, Xiong Z H 2018 ACS Appl. Mater. Inter. 10 1948
Google Scholar
[32] Zhang Q M, Chen L J, Jia W Y, Lei Y L, Xiong Z H 2016 Org. Electron. 39 318
Google Scholar
[33] Obolda A, Peng Q M, He C Y, Zhang T, Ren J J, Ma H W, Shuai Z G, Li F 2016 Adv. Mater. 28 4740
Google Scholar
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Google Scholar
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Google Scholar
Ning Y R, Zhao Q, Tang X T, Chen J, Wu F J, Jia W Y, Chen X L, Xiong Z H 2022 Acta Phys. Sin. 71 087201
Google Scholar
[36] Yuan P S, Qiao X F, Yan D H, Ma D G 2019 J. Mater. Chem. C 7 1035
Google Scholar
[37] Ern V, Merrifield R E 1968 Phys. Rev. Lett. 21 609
Google Scholar
[38] Zhang Z, Yates Jr J T 2012 Chem. Rev. 112 5520
Google Scholar
[39] Jensen K L 2003 J. Vac. Sci. Technol. B. 21 1528
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