ИСТИНА

Here we adopted spin-coating (SC), Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques for formation of low-defect organic semiconductor layers and used it as an active layer in thin-film OFETs. Disiloxane derivatives of BTBT – 1,3-bis[11-(7-hexyl[1]benzothieno[3,2-b][1]benzothien-2-yl)undecyl]-1,1,3,3-tetramethyldisiloxane, O-(Si-Und-BTBT-Hex)2 and 1,3-bis(11-[1]benzothieno[3,2-b][1]benzothien-2-ylundecyl)-1,1,3,3-tetramethyldisiloxane, O-(Si-Und-BTBT)2 have been chosen for this purpose by several reasons. First, because of impressive electrical performance of dialkyl derivatives of the semiconductor core – BTBT (up to 43 cm^2/(Vs) for thick OFETs). Second, BTBT is a promising core for air-stable organic semiconductors. Third, disiloxane fragment included into the molecular structure allows using Langmuir techniques for the layer formation5. For achieving low-defect thin film we tried three alternative ways: surface modification of a substrate; variation of the semiconductor concentration; variation of the processing conditions (rotation velocity for SC and surface pressure for LB or LS). Figure 1 demonstrates AFM scans of monolayer films based on O-(Si-Und-BTBT-Hex)2, which were obtained at optimal conditions by different techniques. To measure the semiconducting properties we have used the patterned substrates with gold electrodes (with channel length 30 μm). All OFETs showed p-type behavior. The linear and saturated hole mobilities, estimated from these measurements, were in the range of 10^(-4) - 10^(-2) cm^2/Vs depending in the preparation conditions. It was found that the presence of terminal aliphatic groups (-Hex) is crucial for the device performance. The best characteristics were obtained for the device based on O-(Si-Und-BTBT-Hex)2 by SC technique: charge carrier mobility of 4*10^(-2) cm^2/Vs and on/off current ratio of 10^6. These OFETs were found to be stable after half-year storage under ambient conditions that enables to use this organic semiconducting compound for sensor applications.