Samsung Advanced Institute of Technology

 The interface between dielectric and organic semiconductor is critically important in determining organic thin-film transistors (OTFTs) performance. Surface polarity of the dielectric layer can hinder charge transport characteristics, which has restricted utilization of polymeric dielectric materials containing polar functional groups. Herein, we fabricated OTFTs and analyzed their electrical characteristics depending on the alkyl chain length of organic semiconductors and surface polarity of polymer dielectrics. High-performance dibenzothiopheno[6,5？b:6′,5′？f]thieno[3,2？b]thiophene (DBTTT) and newly synthesized alkylated derivatives (C6-DBTTT and C10-DBTTT) were utilized as organic semiconductors. As dielectric layers, non-polar poly(1,3,5-trimethyl-1,3,5-trivinylcyclitrisiloxane) (pV3D3) and poly(2-cyanoethyl acrylate-co-diethylene glycol divinyl ether) [p(CEA-co-DEGDVE)] with polar cyanide functionality were utilized. The fabricated OTFTs with pV3D3 commonly exhibited the excellent charge transport characteristics. In addition, the OTFT performance was improved with lengthening the alkyl chain in organic semiconductors, which can be attributed to the molecular orientation of semiconductors. On the other hand, non-alkylated DBTTT OTFTs with polar p(CEA-co-DEGDVE) showed relatively poor electrical characteristics, while their performance was drastically enhanced with the alkylated DBTTTs. The ultraviolet photoelectron spectroscopy (UPS) revealed that surface polarity of the dielectric layer can be abated with alkyl chain in organic semiconductors. We believe this study can provide a useful insight to optimize dielectric/semiconductor interface to achieve high-performance OTFTs.