聚合物级联发光器件

Study on Tandem Polymer Light Emitting Devices

基于溶液加工方法制备了聚乙撑二氧噻吩-聚(苯乙烯磺酸盐)(PEDOT:PSS)/氧化锌(ZnO)/乙氧基化聚乙烯亚胺(PEIE)电荷产生层的聚合物级联发光器件,发现PEDOT:PSS层电导和厚度对器件的电流-电压特性影响较小,不同PEDOT:PSS对器件发光效率的影响主要来自于其对发光层激子不同的猝灭作用,PEDOT:PSS厚度为60 nm的级联器件比PEDOT:PSS厚度为30 nm的级联器件的发光效率稍高,原因是PEDOT:PSS较厚时,其表面形貌更均匀。级联器件的发光效率和驱动电压分别与发光子单元的发光效率和驱动电压之和相近,说明在较低的电压下电荷产生层就能够有效产生电荷并注入到发光子单元中,级联器件的发光光谱中包含两个发光子单元的发光光谱,说明两个发光子单元在级联器件中都能正常工作。通过对电荷产生层的电容-电压(C-V)特性的测试,确认了在电荷产生层中存在电荷的积累过程。证明了PEDOT:PSS/ZnO/PEIE为有效的电荷产生层。首次报道了包含三个SY-PPV发光单元的级联器件,三个发光子单元发光效率之和与级联器件的发光效率相当,其最大发光效率和最大外量子效率分别为21.7 cd·A^(-1)和6.95%。在器件亮度为5 000 cd·m^(-2)时,器件的发光效率和外量子效率分别为20.5 cd·A^(-1)和6.6%。说明并没有由于发光子单元数目增加而影响级联器件的发光效率。并且其发光光谱和发光子单元的发光光谱相接近。通过进一步降低CGL中空穴注入层对级联器件的影响有望提高级联器件的发光效率。

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 of60 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 V_2O_5 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.