Surface-induced film structure for enhanced carrier transport of the conjugated/insulating polymer blends at a low semiconductor content

Abstract

In this work, a donor-acceptor copolymer poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)- alt(3,3‴-di(2-decyltetradecyl)-2,2'; 5′,2''; 5″,2‴-quaterthiophene-5,5‴-diyl)] (PffBT4T-2DT) has been blended with the insulating polystyrene (PS) to fabricate the field-effect transistors (FETs). The blend films deposited on the SiO2 dielectric by the octadecyltrichlorosilane (OTS) modification, exhibit the FET mobility 1–2 orders of magnitude higher than those on the unmodified dielectric, as well as a 10–100 folds enhancement of mobility with decreasing the PffBT4T-2DT ratios at the concentration range of 30 wt. %-5 wt. %. Detailed microstructural characterizations reveal that the OTS modification induces the change of phase-separation structure in the blend film, in which more aggregates of the PffBT4T-2DT are enriched near the semiconductor/dielectric interface. Furthermore, the OTS modification of substrate and the addition of PS facilitate the conversion from face-on to edge-on stacking orientation so that the edge-on packing structure dominates in the films with a semiconductor content of 5–10 wt. %. Based on these results, we propose that the remarkably elevated mobility at low PffBT4T-2DT contents is attributed to the enhanced edge-on arrangement of PffBT4T-2DT as well as the favorable interconnect network of chain aggregates formed at the semiconductor/dielectric interface for efficient carrier transport pathway.