Improvement of hole mobility in organic field-effect transistors based on octyl-substituted oligo-p-phenylenevinylene by thermal treatment at smectic liquid crystalline phase

Organic field-effect transistors based on octyl-subustituted oligo-p-phenylenevinylene have been studied. We have succeeded in improving field-effect hole mobilities by thermal treatment at liquid crystalline phase characterized as a highly ordered smectic phase. The field-effect mobility of the device as vacuum-evaporated was calculated to be 6.9 x 10 (- 3) cm(2) V (- 1) s (- 1) whereas the mobility was enhanced to 1.7 x 10 (- 1) cm(2) V (- 1) s (- 1) after annealing the device at 100 degrees C for 12 h. From the surface morphology of the films observed by using atomic force microscope, the enhancement is found to be attributed to reduction of defect density in the film because of the thermal movement of liquid-crystal molecules. (c) 2008 The Japan Society of Applied Physics.