posted on 2018-05-31, 00:00authored byMichael J. Ford, Ming Wang, Karen C. Bustillo, Jianyu Yuan, Thuc-Quyen Nguyen, Guillermo C. Bazan
Organic field-effect transistors
(OFETs) that utilize ambipolar
polymer semiconductors can benefit from the ability of both electron
and hole conduction, which is necessary for complementary circuits.
However, simultaneous hole and electron transport in organic field-effect
transistors result in poor ON/OFF ratios, limiting potential
applications. Solution processing methods have been developed to control
charge transport properties and transform ambipolar conduction to
hole-only conduction. The electron-acceptor phenyl-C61-butyric acid
methyl ester (PC61BM), when mixed in solution with an ambipolar
semiconducting polymer, can reduce electron conduction. Unipolar
p-type OFETs with high, well-defined ON/OFF ratios and without detrimental
effects on hole conduction are achieved for a wide range of blend
compositions, from 95:5 to 5:95 wt % semiconductor polymer:PC61BM. When introducing the alternative acceptor N,N′-bis(1-ethylpropyl)-3,4:9,10-perylenediimide
(PDI), high ON/OFF ratios are achieved for 95:5 wt % semiconductor
polymer:PDI; however, electron conduction increases for 50:50 and 5:95 wt %
semiconductor polymer:PDI. As described within, we show that electron
conduction is practically eliminated when additive domains do not
percolate across the OFET channel, that is, electrons are “morphologically
trapped”. Morphologies were characterized by optical, electron,
and atomic force microscopy as well as X-ray scattering techniques.
PC61BM was substituted with an endohedral Lu3N fullerene, which enhanced contrast in electron microscopy and allowed
for more detailed insight into the blend morphologies. Blends with
alternative, nonfullerene acceptors further emphasize the importance of morphology
and acceptor percolation, providing insights for such blends that
control ambipolar transport and ON/OFF ratios.