Synthesis and Characterization of Chlorinated Isoindigo-based Polymers Containing Benzodithiophene for Organic Field-Effect Transistors

Abstract

Organic semiconductors recently have attracted a lot of attentions thanks to their significant advantages of light-weight, inexpensive cost and mechanical flexibility. In addition, they are amenable to solution process at low temperature. Organic field-effect transistors (OFETs) are devices using organic semiconductors as the active layer to switch or amplify the electric signal. In order to operate the OFETs, efficient charge injection from the electrodes to the active layer is required. Chlorination is promising method to reduce the charge injection barriers as lowering the energy levels with easy synthesis and high total yield. In this study, we investigated the effect of tuning energy levels by introducing chlorine into isoindigo units. PBDTTCID based on chlorinated isoindigo and benzodithiophene units was synthesized via Stille polymerization, compared with non-chlorinated polymer, PBDTTID. PBDTTCID showed deeper HOMO and LUMO energy levels and narrower band gap than PBDTTID. A top gate/bottom contact (TG/BC) configuration was used to fabricate OFET devices based on two polymers. PBDTTID showed unipolar hole transport characteristics and its hole mobility was 1.80 × 10-2 cm2 V-1 s-1. While PBDTTCID showed ambipolar charge transport characteristics indicating hole and electron mobilities of 2.07 and 6.38 × 10-3 cm2 V-1 s-1, respectively. 2D-GIWAXS and AFM results demonstrated that thermal annealing can improve the device performance by inducing dense molecular packing and favorable morphology for charge transport.