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High Electron Mobility and Ambipolar Charge Transport in Binary Blends of Donor and Acceptor Conjugated Polymers

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  • This research was supported by the Air Force Office of Scientific Research (Grant no. F49620-03-1-0162), the NSF (CTS-0437912) and in part by the Boeing–Martin Professorship Endowment. Work at NTU was supported by the Ministry of Economic Affairs of Taiwan. Supporting Information is available online from Wiley InterScience or from the author.

Abstract

High electron mobility and ambipolar charge transport are observed in phase-separated binary blends of n-type poly(benzobisimidazobenzophenanthroline) (BBL) with p-type polymer semiconductors, poly[(thiophene-2,5-diyl)-alt-(2,3-diheptylquinoxaline-5,8-diyl)] (PTHQx) and poly(10-hexylphenoxazine-3,7-diyl-alt-3-hexyl-2,5-thiophene) (POT). Atomic force microscopy (AFM) and transmission electron microscopy (TEM) show phase-separated domains of 50–300 nm in the binary blend thin films. The TEM images and electron diffraction of BBL/PTHQx blends show the growth of single-crystalline phases of PTHQx within the BBL matrix. A relatively high electron mobility (1.0 × 10–3 cm2 V–1 s–1) that is constant over a wide blend-composition range is observed in the PTHQx blend field-effect transistors (FETs). Ambipolar charge transport is observed in both blend systems at a very high concentration of the p-type semiconductor (≥90 wt % PTHQx or ≥80 wt % POT). Ambipolar charge transport is exemplified by an electron mobility of 1.4 × 10–5 cm2 V–1 s–1 and a hole mobility of 1.0 × 10–4 cm2 V–1 s–1 observed in the 98 wt % PTHQx blend FETs. These results show that ambipolar charge transport and the associated carrier mobilities in blends of conjugated polymer semiconductors have a complex dependence on the blend composition and the phase-separated morphology.

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