Organic semiconductor heterojunctions: electrode-independent charge injectors for high-performance organic light-emitting diodes

Yong-Hua Chen,Dong-Ge Ma,Jiang-Shan Chen,Heng-Da Sun,Qing-Xun Guo,Yong-Biao Zhao,Qiang Wang

doi:10.1038/lsa.2016.42

Abstract

Organic light-emitting diodes (OLEDs) are driven by injected charges from an anode and a cathode. The low and high work function metals are necessary for the effective injection of electrons and holes, respectively. Here, we introduce a fully novel design concept using organic semiconductor heterojunctions (OSHJs) as the charge injectors for achieving highly efficient OLEDs, regardless of the work functions of the electrodes. In contrast to traditional injected charges from the electrodes, the injected charges originate from the OSHJs. The device performance was shown to be significantly improved in efficiency and stability compared to conventional OLEDs. Attractively, the OLEDs based on OSHJs as charge injectors still exhibited an impressive performance when the low work function Al was replaced by air- and chemistry-stable high work function metals, such as Au, Ag, and Cu, as the cathode contact, which has been suggested to be difficult in conventional OLEDs. This concept challenges the conventional design approach for the injection of charges and allows for the realization of practical applications of OLEDs with respect to high efficiency, selectable electrodes, and a long lifetime.

Highlights

A major issue with organic light-emitting diodes (OLEDs) is that electrons and holes should be effectively injected into the emissive layers[1]
Unlike the conventional OLEDs with metals as charge injectors, a C60/pentacene organic semiconductor heterojunctions (OSHJs) is located on each side of the indium tin oxide (ITO) and Al in the studied devices (Figure 1b), where the ITO and Al only play the role of electric contact
It can be observed that the charge carriers for light emission are injected from the OSHJs and not from the metal electrodes, challenging the design of charge carrier injection in conventional OLEDs

Summary

Introduction

A major issue with organic light-emitting diodes (OLEDs) is that electrons and holes should be effectively injected into the emissive layers[1]. The low and high work function metals, have to be employed in the cathode and anode to facilitate the injection of electrons and holes, respectively[2]. This results in drawbacks, including the diffusion of metal ions, such as indium, from a common indium tin oxide (ITO) anode into the emissive layers of OLEDs5 and the accumulation of space charges at the interface due to the injected barriers between electrodes and organic semiconductors[2], which leads to the degradation of device performance over time. By using air- and chemistry-stable high work function metals, such as Au, Ag, and Cu, as the cathode, the degradation effect caused by moisture and oxygen in the air can be avoided

Methods

Results

Conclusion