Ambipolar transport in field-effect transistors based on composite films of poly(3-hexylthiophene) and fullerene derivative

Ambipolar field effects in poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric methyl ester (PCBM) composite films have been studied. At ratios of x = [PCBM]/([P3HT]+[PCBM]) = 0.67-0.9, an ambipolar transport appeared. Hole and electron mobilities were 5.0 x 10(-5) and 2.5 x 10(-4),cm(2)/(Vs), respectively, at x = 0.75. The hole mobility of 1.4 x 10(-3) cm2/(V S) in pure P3HT decreased by blending with PCBM. By increasing the PCBM content, the electron mobility increased to 1.0 x 10(-2) cm(2)/(Vs) in pure PCBM. The threshold voltage in pure P3HT for p-type transport increased upon blending of PCBM, indicating that PCBM depresses the induction of holes. On the other hand, the threshold voltages of PCBM for n-type transport decreased in composite films. The results are discussed taking into consideration the fact that P3HT enhances the induction of electrons in composite films and/or the hole injection from drain to channel.