Charge transport governs the operation and performance of organic diodes. Illuminating the charge-transfer/transport processes across the interfaces and the bulk organic semiconductors is at the focus of intensive investigations. Traditionally, the charge transport properties of organic diodes are usually characterized by probing the current–voltage (I–V) curves of the devices. However, to unveil the landscape of the underlying potential/charge distribution, which essentially determines the I–V characteristics, still represents a major challenge. Here, the electrical potential distribution in planar organic diodes is investigated by using the scanning Kelvin probe force microscopy technique, a method that can clearly separate the contact and bulk regimes of charge transport. Interestingly, by applying to devices based on novel, high mobility organic materials, the space-charge-limited-current-like I–V curves, which are previously believed to be a result of the bulk transport, are surprisingly but unambiguously demonstrated to be caused by contact-limited conduction. A model accounting is developed for the transport properties of both the two metal/organic interfaces and the bulk. The results indicate that pure interface-dominated transport can indeed give rise to I–V curves similar to those caused by bulk transport. These findings provide a new insight into the charge injection and transport processes in organic diodes.
|Original language||English (US)|
|Journal||Advanced Electronic Materials|
|State||Published - Feb 22 2018|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: G.X. and N.G. contributed equally to this work. The authors thank Prof. X. Guo from Shanghai Jiaotong University and Prof. N. Tessler from Technion-Israel Institute of Technology for valuable discussions. This work was supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences, Grant No. XDB12030400, the National 973 Program under Grant No. 2013CB933504, the National Science Foundation of China under Grant Nos. 61221004 and 61505243, Beijing Training Project For The Leading Talents in S & T, No. Z151100000315008, Youth Innovation Promotion Association CAS (Grant No. 2015095), the Opening Project of Key Laboratory of Microelectronic Devices & Integrated Technology, Institute of Microelectronics of Chinese Academy of Science, and Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM).