多层结构的阴极修饰层对有机电致发光器件的性能改善

为提高有机电致发光器件（OLEDs）的阴极电子注入效率，我们设计了新型的阴极杂化修饰层，其结构为Bphen∶LiF/Al/MoO₃，将其应用到器件ITO/NPB/Alq₃/Al中，参考器件的电子注入层选用传统材料LiF。实验研究表明，与传统的阴极修饰层LiF相比，基于这种杂化结构的阴极修饰层非常有效。测试了器件的电致发光光谱（EL谱），其峰值位于534 nm，发光来自于Alq₃，实验中我们可以观察到明亮的绿色发光。将其与传统参考器件的EL谱进行对比，在电流密度40 mA·cm-2下，两个器件的电致发光光谱是一致的。在0～100 mA·cm-2范围内，对器件的EL谱进行了测试。实验结果表明，随着电流密度的增加，器件的发光增强，但是EL谱的形状和谱峰的位置是固定不变的。与参考器件对比，基于杂化修饰层的器件的发光性能更好。研究表明，杂化修饰层的最佳参数为Bphen∶LiF(5 nm; 6%)/Al(1 nm)/MoO₃(5 nm)，在测试范围内，器件的最大电流效率和最大功率效率分别为4.28 cd·A-1和2.19 lm·W-1，相比参考器件提高了25.5%和23.7%。器件的电流密度-电压特性曲线表明阴极杂化修饰层可以增强电子的注入，使器件中的载流子更加平衡，从而提高了器件的发光性能。从两个角度对器件效率的增强进行了理论方面的论证。一方面利用阴极杂化修饰层的作用机制来解释。在HML中，LiF能填充Bphen的电子陷阱，增强电流的注入，同时HML也能限制空穴的传输，减小空穴电流。另一方面从电荷平衡因子的角度，HML增强了电子的注入，使得器件的电荷平衡因子增大，空穴和电子的平衡性更好。实验研究表明，阴极杂化修饰层很好地增强了器件的效率。

Improved Performance with a Hybrid Cathodic Interfacial Layer in OLEDs

To enhance the efficiency of cathode electron injection of organic light-emitting diode (OLEDs), we designed a new hybrid modified layer (HML) with the structure of Bphen: LiF/Al/MoO₃, which was applied to ITO/NPB/Alq₃/Al. The traditional material LiF is used for the electron injection layer of the reference device. The results show that using HBL at the interface between organic and cathode is very effective. We have measured the electroluminescence (EL) spectra of the device. The EL peak of the device is 534 nm, which indicates that it is from Alq₃. It can be seen that the structure design of the multilayer modified layer does not change the luminescence spectrum of the device. Bright green emission can be obtained from the optimized EL devices. Compared with traditional device based on LiF, the performance of the single unit with hybrid modification layer has better luminous properties and efficiency. Present research work shows that when the optimum parameter of the hybrid layer is Bphen∶LiF(5 nm; 6%)/Al(1nm)/MoO₃(5 nm), the maximum current efficiency and the maximum power efficiency of the device are 4.28 cd·A-1 and 2.19 lm·W-1, respectively, which are 25.5% and 23.7% higher than those of the reference device. Current-voltage characteristics demonstrate that the hybrid interfacial layer can promote electron injection, thus increasing the current efficiency and reduced their operating voltage slightly of OLED. We systematically analyze the improvement of device performance from two aspects. On the one hand, LiF can fill the electron trap of Bphen to enhance the current injection, moreover, HML can also block hole transport and reduce the hole current. On the other hand, based on charge balance factor theory, HML enhances the injection of electrons and increases the charge balance factor, which improves the balance of carriers in the device. The experimental results show that the cathode hybrid layer can improve the performance of the device.