Ambipolar Transport in Phase-Separated Thin Films of p- and n-Type Vanadylporphyrazines with Two-Dimensional Percolation

Phase separation in thin films of organic p- and n-type semiconductors has attracted much attention for applications as bulk heterojunctions in organic photovoltaic devices and thin-film transistors (OTFTs). In the present study, we examined the structures, electronic states, and transistor performance of the codeposited thin films of p- and n-type porphyrazines, vanadylphthalocyanine (VOPc), and vanadyltetrakis(1,2,5-thiadiazole)porphyrazine with various mixing ratios. The transistors exhibited ambipolar performance, in which the p-type mobility increases with an increase in the VOPc ratio, and vice versa for the n-type mobility. This can be explained by a phase separation in these thin films. In addition, the mixing ratio dependence of the transistor parameters such as mobility and on/off ratio clearly indicated that the hole and electron carrier transports in the thin films are governed by the two-dimensional percolations of the p- and n-type semiconductor domains, respectively. We also fabricated electric-double-layer transistors of the codeposited thin films with ionic liquid gate dielectrics and found significant improvements in the mobility and threshold voltage and a high on/off ratio. The complementary inverters composed by these OTFTs worked in the first and third quadrants with a large signal gain over 10.