Bulk heterojunction bipolar field-effect transistors processed with alkane dithiol

Bipolar filed-effect transistors (BiFETs) fabricated from bulk heterojunction (BHJ) materials comprised of various ratios of the small bandgap polymer, poly[ 2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT), and the soluble fullerene, [6,6]-phenyl-C71butyric acid methyl ester (PC71BM) are reported. We focus on the effect of the addition of small concentrations of the processing additive, 1,8-octanedithiol (ODT), on the gate-induced transport properties. Processing with the ODT additive increased the mobilities of holes (on the PCPDTBT) and electrons (on the PC71BM). If, however, the ODT was not completely removed from the BHJ films, the hole mobility actually decreased, implying that residual ODT functions as a hole trap. (C) 2008 Elsevier B.V. All rights reserved.