The Study of Working Mechanism of Organic Heterojunction Charge Generation Layer

Abstract

The tandem organic light-emitting diodes (tandem OLEDs), which having two or more electroluminescence (EL) units vertically stacked in series through charge generation layer (CGL), were widely used in flat-panel displays and solid state lighting because of their advantages of enhanced current efficiency and luminance at low current densities, as well as their prolonged lifetime as compared to the conventional single-unit devices. In a tandem OLEDs, the CGLs play an important role, serving as the charge generation layer, and it is critical for the performance of tandem OLEDs. It is the basis of fabrication high-efficiency tandem OLEDs to deeply understand the working mechanism of CGL. Organic heterojunctions (OHJs) layers are frequently used as CGLs in the construction of high-efficiency tandem OLEDs. In order to understand the working mechanism of organic heterojunctions CGLs, the device with the structure of glass/ITO/tris(8-hydroxyquino line) aluminium (Alq3) (60 nm)/C60(x nm)/pentacene((40-x) nm)/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) (40 nm)/Al (100 nm) were successfully fabricated, here the organic heterojunction C60/pentacene was used as CGL. The experiment results demonstrated that the organic heterojunction CGL with the structure of C60 (15 nm)/pentacene (25 nm) with the most effective charge generation ability. By analyzing the carrier transport characteristics in device, the device current can be attributed to the organic heterojunction CGL. Finally, by numerically analyzing the current–voltage (J–V) characteristics of devices, the results showed the charge generation mechanism of organic heterojunction was in accord with quantum tunneling process. The obtained results can help ones deeply understand the working mechanism of organic heterojunction CGLs and fabricate high-efficiency OLEDs.