Alq基有机发光二极管中Liq的“n型掺杂”机理研究

Mechanism of Liq's “N-Type Doping” in Alq Based Organic Light-Emitting Diodes

摘要:

通过将Liq(8-hydroxyquinolinato-lithium)掺入电子传输层Alq(tris(8-hydroxyquinolinato)aluminum)中,制备了具有不同结构的仅传输电子的单载流子器件。实验结果表明,掺杂器件的电性能劣于含Liq/Al复合阴极的非掺杂器件,优于含Al阴极的非掺杂器件,这表明掺入Alq的Liq没有产生明显的“n型掺杂”效应,其具有双重作用:掺杂后分散在Alq/Al阴极界面上的Liq以电子注入层的形式出现,通过增强电子注入来提高器件电流；掺杂后存在于Alq体相中的Liq由于自身的导电性差,对电子传输具有不利影响,从而降低了器件的电流。在电致发光器件的测试中,Liq的掺杂表现出类似的现象,掺入Liq的器件性能介于非掺杂具有Liq/Al阴极和Al阴极结构器件之间,三种器件的最大电流效率分别为3.96,4.27和2.27cd/A,并且在吸收光谱和光致发光光谱中观察不到电荷转移所带来的额外变化。

Abstract:

Electron-only devices with different structures were prepared by doping Liq (8-hydroxyquinolinato-lithium) into the electron transport layer Alq (tris(8-hydroxyquinolinato) aluminum). The experimental results show that the electrical properties of doped devices are inferior to those of non-doped devices with Liq/Al composite cathodes and superior to those of non-doped devices with Al only cathodes. This indicates that Liq’s doped with Alq does not show any significant “n-doping” effect. The effect exhibits dual roles:Liq molecules dispersed at the Alq/Al cathode interfaces after doping display as electron injection layers, which enhances the device currents by enhancing electron injection; those in the bulk of Alq after doping have a detrimental effect on electron transport due to their own poor conductivity, consequently decrease the device currents. In the tests of electroluminescent devices, the doping of Liq shows a similar behavior. The performance of Liq-doped device is between the non-doped devices with Liq/Al cathode and Al cathode structures, with maximum current efficiencies of 3.96,4.27 and 2.27cd/A for the three devices, respectively, and no additional changes caused by charge transfer are observed in the absorption and photoluminescent spectra.