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摘要:量子点发光二极管(QLEDs)由于具有独特的光电特性，可应用于照明和显示行业，其外量子效率（EQEs）正迅速接近商业化要求。然而，器件的稳定性和工作寿命仍然是QLEDs商业化应用面临的关键问题。本文将影响QLEDs寿命的主要因素分为功能层材料的稳定性和电荷注入不平衡两大方面，从提高量子点、电荷传输层(CTLs)的稳定性以及促进电荷平衡等方面讨论了近年来提高QLEDs稳定性的各种策略。随着人们对QLEDs降解机制认识的加深，更稳定的量子点和QLEDs器件得以开发，但是将QLEDs器件商业化仍存在很大的挑战，比如Cd的高毒性以及蓝光QLEDs的寿命和效率远低于绿光和红光相对应的水平，此外，QLEDs在高亮度(1000 cd m –2)下的稳定性较差，这些因素均限制了QLEDs的发展。因此，应进一步加大QLEDs在光电器件领域的研发力度，克服这些技术劣势，实现QLEDs未来的商业化。Abstract:Quantum dot Light-Emitting Diodes (QLEDs) are applied to the lighting and display industry for their unique photoelectric characteristics. Their External Quantum Efficiency (EQEs) is quickly meeting commercial requirements while the device’s lifetime is still one of their biggest challenges. The significant factors affecting the lifetime of QLEDs are divided into two aspects including the stability of the functional layer’s materials and charge imbalance. Various strategies for enhancing QLEDs stability are discussed including improving the stability of quantum dots, implementing Charge Transport Layers (CTLs) and promoting charge balance. With the deepening understanding of the degradation mechanism of QLEDs, more stable quantum dots and QLEDs devices have been developed. However, there are still some obstacles to the commercialization of QLEDs. For example, the high toxicity of Cd and the lifetime and efficiency of blue QLEDs are far lower than the corresponding levels of green and red QLEDs. In addition, the stability of QLEDs at high brightness (1000 cd m −2) is usually much shorter, which still limits the development of QLEDs. Therefore, research and development efforts for QLEDs should be further strengthened to overcome these technical obstacles and achieve the future commercialization of QLEDs.
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图 3(a)由电极、电荷注入层(CILs)、电荷传输层(CTLs)和QDs发光层(EML)组成的QLEDs结构图；(b) QLED能级简图及其工作机理；(c)几种常用的CTLs以及不同发光颜色的合金量子点的能级比较[10]
Figure 3.(a) Schematic diagram of QLEDs consisting of electrodes, charge injection layers (CILs), charge transport layers (CTLs), and a QD’s emitting layer (EML). (b) Brief energy level diagram of a QLED and its working mechanism. (c) Band energy levels of some commonly used CTLs compared with that of alloyed QDs with different emission colors[10]
图 4QLED量子点发射层的光学特性变化。(a) 使用CdSe/Zn0.5Cd0.5S QD的QLED在持续工作90 min下的IQE（黑色实线）和QLED的工作电压（黑色虚线）随时间变化的轨迹图，操作条件：电流密度为30 mA / cm2，QD发射薄膜的PLQY（红色圆圈），叠加反向电压（−7 V，青色正方形）并额外冷却1小时（蓝色三角形）的QD发射层的PLQY；(b) QLED中充电、热量和量子点的永久性降解对工作90 min后的量子点发射层的发光效率降低的贡献；(c)~(e)分别表示在操作0、5、30、60、90 min之后以及在施加反向电压(−7 V，青色)和冷却1 h(蓝色)之后的量子点发射层的归一化PL衰减曲线(插图：在10 ns时间延迟时用PL强度归一化的PL衰减曲线)[33]
Figure 4.Changes in the optical characteristics of the QD emissive layer during operation. (a) Operation time-dependent traces of IQE (black solid line) and the operation voltage (black broken line) of the QLED employing CdSe (r= 2.0 nm)/Zn0.5Cd0.5S (h= 6.3 nm) QDs under continuing operation at a current density of 30 mA/cm2and a PLQY (red circle) of the QD emissive film in the corresponding device. The PLQYs of the QD emissive layer in the QLED after 90 minutes of operation after applying reverse voltage (−7 V, cyan square) and additional cooling for 1 h (blue triangle) are overlaid for comparison. (b) Contributions of charging, heat, and the permanent degradation of QDs to the reduction of luminescence efficiency of the QD emissive layer in a 90-min-operated QLED. Normalized PL decay curves of the QD emissive layer after operation for 0, 5, 30 min (c), 30, 60, 90 min (d) and (e) after applying reverse voltage (−7 V, cyan) and cooling for 1 h (blue) (insets: PL decay curves normalized with the PL intensities at 10 ns of time delay)[33]
图 5(a) 用OA或DDT配体合成的QDs示意图；(b) QD-OA和(c)QD-DDT的变温稳态PL光谱，将样品从20 ℃加热到140 ℃（左），然后从140 ℃冷却到20 ℃（右）。插图显示了QD-OA和QD-DDT中不同的表面缺陷状态[56]
Figure 5.(a) Schematic diagrams of QDs modified with OA or DDT ligands. Temperature-dependent steady PL spectra of (b) QD-OA and (c) QD-DDT. The samples were heated from 20 ℃ to 140 ℃ (left) and then cooled from 140 ℃ to 20 ℃ (right). The insets show the different surface trap states in the QD-OA and QD-DDT[56]
图 6(a) 各层材料的能级图[89]；(b) 有无Al2O3夹层的QLEDs的效率滚降图, 插图显示ZnO/Al2O3的表面粗糙度[89]；(c) 有无Al2O3中间层的QLEDs器件寿命比较[89]；(d) 红光倒置QLED的器件结构[90]；(e) EQE和功率转换效率(PCE)与电压的关系图[90]；(f) 器件的稳定性比较，在温度为21-24 ℃以及相对湿度为40-60%的条件下测定其稳定性[90]
Figure 6.(a) Band energy level diagram of each material[89]. (b) Efficiency roll-off of QLEDs without and with an Al2O3interlayer. The inset shows the surface roughness of ZnO/Al2O3[89]. (c) Device lifetime of the QLEDs without and with the Al2O3interlayer[89]. (d) The device structure of the red inverted QLEDs[90]. (e) EQE and power conversion efficiency (PCE) versus the voltage characteristics of the devices[90]. (f) Device stability. The stabilities were measured under ambient conditions (temperature: 21~24 ℃; relative humidity: 40%~60%)[90]
表 1QLEDs的器件结构、性能和寿命
Table 1.Device structures, performances and lifetimes of QLEDs
器件结构 量子点结构 QLED颜色 EL峰位（nm） VON（V） EQE （%） 寿命 Ref ITO/PEDOT:PSS/TFB/QDs/ZnO/Al CdSe/Cd1-xZnxSe/ZnSe 红 631 1.7 15.1 2260000 h@T50,
100 nit (n=1.80)[8] ITO/PEDOT:PSS/poly-TPD/PVK/
QDs/ZnO/AgCdSe/ CdS-RNH2 红 625 1.65 20.2 90000 h@T50,
100 nit (n=1.80)[37] ITO/PEDOT:PSS/poly-TPD/PVK/
QDs/ZnMgO/AgCdSe–CdZnS 红 624 1.7 18.2 190000 h@T50,
100 nit (n=1.80)[38] ITO/PEDOT:PSS/TFB/QDs/ZnO/Al Zn1−xCdxSe/ ZnSe/ZnS 红 602 1.8 30.9 1800000 h@T50,
100 nit (n=1.84)[6] ITO/PEDOT:PSS/TFB/QDs/ZnO/Al CdSe/ZnCdSe/ZnSe 红 − − 21.6 1600000 h@T50,
100 nit (n=1.78)[2] ITO/ZnO/QDs/CBP/TCTA/NPB/
HATCN/AlCdSe/ZnS 红 630 − 11.1 864000 h@T50,
100 nit (n=1.80)[39] ITO/V2O5/PEDOT:PSS/TFB/QDs/Au ZnCdSeS/ZnS 绿 530 2.1 18.09 13355 h@T50,
100 nit (n=1.50)[40] ITO/PEDOT:PSS/TFB/QDs/ZnO/Al ZnCdSe/ZnSe/ZnSeS/ZnS 绿 527 2.3 23.9 1655000 h@T50,
100 nit (n=1.77)[7] ITO/PEDOT:PSS/TFB/QDs/ZnO/Al CdSe/ZnSe 绿 − − 22.9 1760000 h@T50,
100 nit (n=1.82)[2] ITO/PEDOT:PSS/poly-TPD/PVK/
QDs/ Zn0.9Mg0.1O/AlCdSeS/ZnSeS / ZnS-RNH2 蓝 − − 10 10000 h@T50,
100 nit (n=1.88)[37] ITO/PEDOT:PSS/TFB/QDs/ZnO/Al ZnxCd1–xSe/ZnSe 蓝 476 − 8.05 7000 h@T50,
100 nit (n=1.64)[2] ITO/PEDOT:PSS/poly-TPD/
PVK/QDs/ ZnO/AlCdSe/ZnS 蓝 460 2.7 12.80 32705 h@T50,
100 nit (n=1.80)[41] 
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表 2常见ETL的材料参数
Table 2.Parameters of common ETL materials
材料 电子迁移率/ (cm2v−1s−1) 与Al电极间势垒差/(eV) TiO2 10-4 0.4 Alq3 10-5 1.2 ZnO 1.8×10−3 <0.4 下载:
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表 3常见HTL材料的参数
Table 3.Parameters of common HTL materials
材料 HOMO/LUMO (eV) 空穴迁移率/ (cm2v−1s−1) TFB 5.4/2.3 1×10−2 PVK 5.8/2.2 2.5×10−6 poly-TPD 5.2/2.3 1×10−4 TPD 5.4/2.3 1.1×10−5 TCTA 5.7/2.4 1×10−5 CBP 5.9/2.9 1×10−3 下载:
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