Silaindacenodithiophene based organic semiconductor for high performance organic field-effect transistors

To study the structure-property relationship of silaindacenodithiophene (SiIDT) based semiconducting small molecules, new donor-acceptor type organic small molecules, LGC-D050, LGC-D075 and LGC-D117 are synthesized. These molecules are composed of SilDT as the electron-donating core and diketopyrrolopyrrole (DPP, LGC-D050 and LGC-D117) or mono-fluoro-benzothiadiazole (FBT, LGC-D075) as the electron-accepting linkers and alkylrhodanine as the electron-accepting end groups. Both LGC-D050 and LGC-D117 have the same backbone structure but different side chains, such as 2-ethylhexyl attached to SilDT and n-octyl to rhodanine for LGC-D117, and n-octyl to SilDT and ethyl to rhodanine in LGC-D050, to check the effect of alkyl chain length. Top-gate/bottom-contact organic field-effect transistors (OFETs) with LGC-D050 show the best p-type field-effect mobility with a maximum of 1.14 cm2V−1s−1 (average 0.83 ± 0.22 cm2V−1s−1) after 140 °C annealing comparing to LGC-D075 (maximum of 0.90 cm2V−1s−1) and LGC-D117 (maximum of 0.69 cm2V−1s−1). Meanwhile, LGC-075 also show n-type mobility up to 0.93 cm2V−1s−1 after 140 °C annealing, result to a balanced ambipolar charge transport. The best device performance of LGC-D050 is achieved by the combination of SilDT with the n-octyl-alkyl chain and DPP as the linker and ethyl rhodanine as the electron accepting end group, due to its high-ordering and low contact resistance compared to the branched alkyl chain to SilDT and the octylrhodanine end group (LGC-D117), and FBT linker and the octylrhodanine end group (LGC-D075).