Fig. 2. Electrical characteristics and morphology of the cPBPB OFETs. (a) Transfer curve for cis-cPBPB; (b) transfer curve for trans-cPBPB. Device current (left axis, black) and square root of current (right axis, red or blue) measured as a function of gate voltage at a constant source-drain voltage of 80 V. The trans-cPBPB device has a higher current than the cis-cPBPB at a high and positive gate voltage, indicating a higher mobility for n-type carriers. (c) Height image for cis-cPBPB and (d) trans-cPBPB. Both films are continuous and smooth and have a root mean square roughness of 0.35 and 0.37 nm for the cis and trans-based devices, respectively. The scale bar is 1.0 μm.