Alkyl side-chain engineering of dithieno[3,2-b:2′,3′-d]thiophene-based small-molecular semiconductors for solution-processed organic field-effect transistors and complementary-like inverters

초록

Three small-molecular organic semiconductors based on dithieno[3,2-b:2 ',3 '-d]thiophene (DTT) bearing linear octyl, branched 2-ethylhexyl, or linear dodecyl side chains were synthesized to investigate the effect of alkyl chain architecture on thin-film microstructure and charge transport in solution-processed organic field-effect transistors (OFETs). Their thermal stability and phase behavior were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and their optical and electrochemical properties were characterized by UV-vis spectroscopy and cyclic voltammetry (CV), respectively. X-ray diffraction (XRD) and atomic force microscopy (AFM) analyses of the solution-sheared semiconductor films revealed that the DTT derivative with linear octyl substituents (compound 1) exhibited a more pronounced (001) diffraction response and well-developed terrace-like morphology than the branched analogue. This favorable thin-film organization translated into the highest OFET performance for compound 1 among DTT compounds, with a maximum hole mobility of 0.69 cm2 V-1 s-1 and a current on/off ratio similar to 109 under ambient conditions. Extending the linear side chain from octyl to dodecyl maintained appreciable p-channel transport but reduced the mobility, whereas introducing a branched 2-ethylhexyl side chain markedly suppressed charge transport. These results demonstrate that side-chain architecture plays a decisive role in molecular assembly and charge transport in DTT-based small-molecular semiconductors. Furthermore, compound 1 was blended with a non-fullerene acceptor as an n-type acceptor component to fabricate bulk-heterojunction ambipolar transistors, and complementary-like inverters based on two identical ambipolar transistors exhibited an inverting response with a maximum voltage gain of up to 39.

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