Unidirectionally Crystallized Stable n-Type Organic Thin-Film Transistors Based on Solution-Processable Donor-Acceptor Compounds

Thin-film formation by solution-shearing technique is examined for layered-crystalline donor-acceptor charge-transfer compounds composed of 2,7-dioctyl[1] benzothieno[3,2-b][ 1] benzothiophene as a donor and optionally fluorinated derivatives of tetracyanoquinodimethane (n = 0, 2, 4) as acceptors. Polycrystalline thin films of the compounds whose crystalline size is over 2 mm along the blade-scan axis are successfully fabricated, and the formed films demonstrate anisotropic alignment of the crystalline grains where the crystal a-axis with the largest transfer integral is parallel to the blade-scan axis. Such anisotropic alignment of large crystalline grains affords air-stable n-type field-effect operation with a mobility as high as 0.61 cm(2) V-1 s(-1) which is comparable to that of the single-crystal devices.