Ir配合物染料调节有机发光二极管发光特性

摘要

Through doping different organic dyes in organic light-emitting diodes ( OLEDs) with the same structures, we hope to investigate the relationship between the energy gaps of the doped dyes and the emission wavelength of the devices, as well as to analyze the energy transfer mechanism in the system. The structure of the OLED is ITO/NPB/CBP∶dyes /TPBi/Mg∶Ag/Ag, and the doped organic dyes include Ir( MDQ) 2 ( acac) , Ir( ppy) 3 and Firpic. The three doped devices have almost the same threshold voltages and emit red, green and blue light, respectively. At an luminance of 100 cd/m2 , the green-light device doped Ir( ppy) 3 achieves the highest external quantum efficiency of 7. 64%. Meanwhile, the red-light device doped Ir(MDQ)2(acac) has the external quantum effi-ciency of 2. 75%, which is the lowest one among the three devices, while the blue-light one doped Firpic achieves an external efficiency of 5 . 65%. The differences of the emission wavelength and the external quantum efficiency of those devices are assigned to the difference of the energy gaps of the dyes. Further analysis also shows that energy transfer between the CBP and the dyes exists.%为了研究有机发光二极管( OLED)中发光特性与材料能带结构的关系,把不同的Ir配合物染料掺杂到结构相同的OLED器件中。 OLED结构为ITO/NPB/CBP∶染料/TPBi/Mg∶Ag/Ag,染料分别为Ir(MDQ)2(acac)、Ir(ppy)3和Firpic。实验表明,这3种染料对应的掺杂器件分别发红光、绿光和蓝光。3个器件的阈值电压基本一致((6±0.1) V),但是,在100 cd/m2亮度下,绿光器件外量子效率最高(7.64%),蓝光器件外量子效率(5.65%)与绿光相近,红光器件外量子效率最低(2.75%)。分析认为,由于染料的掺杂浓度低,器件结构和载流子传输特性变化小,因而掺杂对阈值电压影响小；CBP与掺杂染料间存在能量转移,红色染料能级差小,非辐射跃迁几率大,发光效率最低；相比于绿光,蓝色染料能级差大,跃迁几率小,因此发光效率比绿光低。实验还发现,染料的发光波长与其能级差相比有红移现象,分析认为,这是由激发态能量振动弛豫和系间窜越过程形成的。