Lei Yong, Liu Zhen, Fan Chang-jun, Ji Xia-xia, Peng Xue-feng, Li Guo-qing, Yang Xiao-hui
Guang Pu Xue Yu Guang Pu Fen Xi. 2017 Mar;37(3):715-22.
We report tandem polymer light emitting devices by using the PEDOT∶PSS/ZnO/PEIE charge generation layer (CGL) and investigate the influences of the conductance and thickness of PEDOT∶PSS layer on the properties of the devices. The results indicate that the conductance and thickness of PEDOT∶PSS layer have marginal impact on the J-V characteristics of the devices, while significant influences of device efficiency upon utilization of different PEDOT∶PSS specimens mainly come from their different strengths on exciton quenching. Luminance efficiency of TOLEDs with the PEDOT∶PSS thickness of 60 nm in CGL is better than TOLEDs with the PEDOT∶PSS thickness of 30 nm in CGL, the reason is that PEDOT∶PSS thickness of 60 nm the surface topography is more even . Luminance efficiency and driving voltage of the tandem devices match the sum of the luminance efficiency and driving voltage of the component light-emitting units, respectively, indicating that charges generated in the CGL can be injected efficiently into the adjacent light-emitting units. Incorporation of a V2O5 layer into the CGL structure only slightly affects the J-V and LE-I characteristics of the tandem devices, suggesting that the utilization of the PEDOT∶PSS/ZnO/PEIE CGL enables the simplification of the CGL structure without compromising device performance. The luminescence spectra of TOLEDs obviously involves two light emitting unit of spectrum, which shows that two light emitting unit in TOLEDs is normal work. Measurements on the capacitance-voltage characteristics of the CGL-based devices confirm that under negative bias (ITO anode) charges are accumulated and displaced in the CGL, which is totally in line with the full operation of light emitting units in the tandem devices. PEDOT∶PSS/ZnO/PEIE layer is evidenced the effective CGL. On this basis, for the first time we report tandem polymer light emitting devices containing three SY-PPV light-emitting units，which show the mixture of luminance efficiency and external quantum efficiency of 21.7 cd·A-1 and 6.95%, similar to the total luminance efficiency and external quantum efficiency of constituent LEUs. At 5 000 cd·m-2, the luminance efficiency and external quantum efficiency of the tandem devices are 20.5 cd·A-1 and 6.6%. Thus, the increase in the number of light emitting units leads to almost no performance losses, implying the robustness of the PEDOT∶PSS/ZnO/PEIE CGL. Tandem polymer light emitting devices containing three SY-PPV light-emitting units of the luminescent spectra is close to the light emitting unit. Further efforts on the optimization of hole injection layer in the CGL to minimize exciton quenching are underlying to promote the luminance efficiency of tandem polymer light emitting devices.
我们报道了采用PEDOT∶PSS/ZnO/PEIE电荷产生层（CGL）的串联聚合物发光器件，并研究了PEDOT∶PSS层的电导率和厚度对器件性能的影响。结果表明，PEDOT∶PSS层的电导率和厚度对器件的J-V特性影响较小，而不同PEDOT∶PSS样品对器件效率的显著影响主要源于它们对激子猝灭的不同强度。CGL中PEDOT∶PSS厚度为60 nm的顶发射有机发光二极管（TOLED）的发光效率优于CGL中PEDOT∶PSS厚度为30 nm的TOLED，原因是PEDOT∶PSS厚度为60 nm时表面形貌更均匀。串联器件的发光效率和驱动电压分别与组成发光单元的发光效率和驱动电压之和相匹配，这表明在CGL中产生的电荷可以有效地注入相邻的发光单元。在CGL结构中加入V2O5层仅对串联器件的J-V和发光效率-电流（LE-I）特性有轻微影响，这表明使用PEDOT∶PSS/ZnO/PEIE CGL能够简化CGL结构而不影响器件性能。TOLED的发光光谱明显包含两个发光单元的光谱，这表明TOLED中的两个发光单元正常工作。对基于CGL的器件的电容-电压特性的测量证实，在负偏压（ITO阳极）下，电荷在CGL中积累和移动，这与串联器件中发光单元的全工作状态完全一致。PEDOT∶PSS/ZnO/PEIE层被证明是有效的CGL。在此基础上，我们首次报道了包含三个SY-PPV发光单元的串联聚合物发光器件，其发光效率和外量子效率分别为21.7 cd·A-1和6.95%，与组成发光单元的总发光效率和外量子效率相似。在5000 cd·m-2时，串联器件的发光效率和外量子效率分别为20.5 cd·A-1和6.6%。因此，发光单元数量的增加几乎不会导致性能损失，这意味着PEDOT∶PSS/ZnO/PEIE CGL的稳健性。包含三个SY-PPV发光单元的串联聚合物发光器件的发光光谱与发光单元接近。进一步努力优化CGL中的空穴注入层以最小化激子猝灭是提高串联聚合物发光器件发光效率的基础。
