Modulation of carrier mobility of diketopyrrolopyrrole and quaterthiophene containing copolymer with self-assembled monolayers on gate dielectrics of thin film transistors

• Self-assembled monolayers (SAMs) were prepared with OTS and ODTS on SiO2/Si for TFT fabrication.
• The polymer film on ODTS-SAM showed high crystallinity and surface uniformity.
• TFT prepared with ODTS-SAM exhibited highest hole mobility.

We fabricated organic thin-film transistors (OTFTs) using diketopyrrolopyrrole (DPP) and quaterthiophene (QT) containing a conjugated polymer, poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2′:5′,2″:5″,2‴-quaterthiophene] (P(DPP-alt-QT)), as an active layer, with chemically modified SiO2 gate dielectrics. The effect of the surface treatment of SiO2 with alkyltrichlorosilanes on the electric characteristics of P(DPP-alt-QT) was investigated. The self-assembled monolayers (SAMs) were elaborated with n-octyltrichlorosilane (OTS) and n-octadecyltrichlorosilane (ODTS) on the SiO2 surface.After the treatment with SAM, the contact angles and surface free energy of the dielectric layers were measured to study the variation in the surface properties. Using a high-performance P(DPP-alt-QT) polymer, we fabricated thin-film transistor devices with the following dielectric layers: bare SiO2/Si, OTS-SiO2/Si, and ODTS-SiO2/Si. In the electrical measurements, typical I–V characteristics of TFTs were observed. The values of best field-effect mobility, μ, were 1.13 and 3.46 cm2 V−1 s−1 for P(DPP-alt-QT)-based TFTs containing OTS- and ODTS-treated SiO2 dielectric layers, respectively. The ODTS-treated TFT device with the lowest dielectric surface free energy exhibited the highest mobility among the three devices constructed using three different dielectric layers.

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