Hall Effect of Solution-crystallized and Vapor-deposited 2,7-Dioctylbenzothieno[3,2-b]Benzothiophene Field-effect Transi
- PDF / 179,468 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 213 Views
1270-II06-20
Hall effect of solution-crystallized and vapor-deposited 2,7-dioctylbenzothieno[3,2-b]benzothiophene field-effect transistors M. Yamagishi1, T. Uemura1,2, Y. Takatsuki1, J. Soeda1, Y. Okada1, Y. Hirose1, Y. Nakazawa1, S. Shinamura3, K. Takimiya3, and J. Takeya1,2 1 Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan. 2 ISIR, Osaka University, Ibaraki 567-0047, Japan. 3 Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan.
ABSTRACT Gate-voltage dependent Hall coefficient RH is measured in high-mobility field-effect transistors of solution-crystallized and vapor-deposited 2,7-dioctylbenzothieno[3,2-b]benzothiophene. The value of RH evolves with density of accumulated charge Q, precisely satisfying the free-electron formula RH = 1/ Q near room temperature. The result indicates that the intrinsic charge transport inside the grains is band-like in the high-mobility organic-semiconductor thin films that are of significant interest in industry. At lower temperatures, even Hall-effect mobility averaged over the whole polycrystalline film decreases due to the presence of carrier-trapping levels at the grain boundaries, while the free-electron-like transport is preserved in the grains. With the separated description of the inter- and intra-grain charge transport, it is demonstrated that the reduction of mobility with decreasing temperature often shown in organic thin-film transistors does not necessarily mean mere hopping transport. INTRODUCTION Organic field-effect transistors (OFETs) have been intensively investigated because of their capability of applications to flexible, light-weight, large-area and low-cost next-generation electric devices. In terms of the maximum field-effect mobility, development of organic singlecrystal transistors disclosed that even the value of more than 20 cm2/Vs is reachable for practical OFETs and that the high-mobility transport is based on a diffusive transport. However, they have difficulties in producing commercial components because crystals are grown independently of substrates. Vapour-deposited polycrystalline thin films usually show one-order less performance, though they have moderate accessibility to large-scale application. On the other hand, solution processes are the most suitable to large-scale and low-cost fabrication but have suffered from low mobility. However, very recently, we develop a method to fabricate crystalline thin films from solution showing high carrier mobility exceeding a few cm2/Vs. In order to understand carrier transport mechanism of practically useful solution-processed crystalline films and vapourdeposited polycrystalline films, we measured Hall effect, which can directly examine that the microscopic in-grain transport mechanism separated from effects of grain boundaries. In the present experiments, we focus on recently synthesized semiconducting material, 2,7-dioctylbenzothieno[3,2-b]benzothiophene (C8-BTBT), which shows carrier mobilities as high as ~3 cm2/Vs in both vapour-deposited polyc
Data Loading...
