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

• Published in: Light, science & applications Vol. 5; no. 3; p. e16042
• Main Authors: Chen, Yong-Hua, Ma, Dong-Ge, Sun, Heng-Da, Chen, Jiang-Shan, Guo, Qing-Xun, Wang, Qiang, Zhao, Yong-Biao
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.03.2016; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/624/1020/1091; 639/624/1075/401; Applied and Technical Physics; Atomic; Cathodes; Cathodic protection; Charge; Classical and Continuum Physics; Electrodes; Heterojunctions; Injectors; Lasers; Molecular; Optical and Plasma Physics; Optical Devices; Optics; Organic light emitting diodes; Organic semiconductors; Original; original-article; Photonics; Physics; Physics and Astronomy; Work functions; charge injection; organic semiconductor heterojunctions; OLEDs
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2016.42

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. Organic light-emitting diodes: electrode-independent charge injection The use of organic semiconductor heterojunctions has enabled electrode-independent charge injection in organic light-emitting diodes (OLEDs). Conventionally, metals with high and low work functions are respectively used to achieve effective injection of electrons and holes in OLEDs. Now, Yonghua Chen and co-workers in China, the USA and Singapore have used a C 60 /pentacene semiconductor heterojunction to realize highly efficient OLEDs in which charge injection is independent of the electrode work function. The OLEDs exhibited enhanced efficiency and stability over conventional OLEDs. This high performance was maintained even when the low work function aluminium electrode was replaced with high work function electrodes made from gold, silver and copper – metals that are chemically unreactive and stable in air. The researchers anticipate that this new design concept will greatly extend the range of electrodes that can be used in OLEDs.