Heteroatom Substitution of Oligothienoacenes: From Good p-Type Semiconductors to Good Ambipolar Semiconductors for Organic Field-Effect Transistors

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• 作者：Yuexing Zhang ; Xue Cai ; Yongzhong Bian ; Xiyou Li ; Jianzhuang Jiang
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：April 3, 2008
• 年：2008
• 卷：112
• 期：13
• 页码：5148 - 5159
• 全文大小：264K
• 年卷期：v.112,no.13(April 3, 2008)
• ISSN：1932-7455

文摘

Density functional theory calculations were carried out to investigate the effect of oligomer length, halogensubstitution, and heteroatom substitution on the organic field-effect transistor (OFET) performance of a seriesof oligothienoacenes (1-5 for oligothienoacene with thiophene units' number from two to six). Compounds1-5 are revealed to act only as p-type semiconductors due to their very high electron injection barrier relativeto the work function potential of Au source-drain electrodes. Heteroatom substitution of the thiophene sulfuratom in particular with boron in the fused-ring thiophene oligomer 5 was revealed to elevate the HOMOenergy level and lower the LUMO energy level and therefore lower both the hole and electron injectionbarriers. However, halogen substitution cannot effectively improve the electron injection barrier, but significantlyincreased the reorganization energy, therefore leading to decreased transfer mobility. The appropriate ionizationpotential and electron affinity, balanced charge injection barrier for both hole and electron relative to thework function potential of Au source-drain electrodes, low hole and electron reorganization energy, and goodintrinsic transfer mobility for both hole and electron of both the boron-substituted hexathienoacenes 5BHand 5BH-2F-a make these two compounds good potential semiconductors for ambipolar OFET devices,with calculated intrinsic charge-transfer mobilities achieving 3.74 and 5.07 cm² V^-1 s^-1 for hole and 4.77and 5.76 cm² V^-1 s^-1 for electron, respectively. The high intrinsic mobilities of 5BH and 5BH-2F-aare rationalized in terms of their frontier orbitals, molecular structure variation upon oxidation andreduction, and electron coupling between two neighboring molecules. All the results indicate that heteroatomsubstitution of sulfur atoms in oligothienoacenes is a rational way toward good ambipolar OFET semiconductingmaterials.