Effect of molecular orientation on carrier transport in organic field‐effect transistors based on newly synthesized liquid crystalline compounds

Abstract

AbstractWe fabricated organic field‐effect transistors (OFETs) based on the liquid crystalline compound which was newly synthesized to enhance carrier‐transport ability. Large conduction anisotropy depending on the carrier‐transport channels was observed in the OFETs fabricated using oblique evaporation, which was probably due to the anisotropic molecular alignment in the liquid crystalline films. The carrier‐transport properties of OFETs depended on the deposition rate of liquid crystalline materials. The mobilities increased up to 2.6×10–2 cm2/Vs as the deposition rates decreased. To estimate the degree of molecular orientation in liquid crystalline films with different deposition rates, polarization‐resolved photoluminescence was measured, and we found that the molecular orientation improved with decrease in the deposition rate. Atomic force microscopy was performed for liquid crystalline films with different deposition rates, and we did not observe large differences of surface features depending on the deposition rates, suggesting that the deposition rate influenced more significantly on the molecular orientation than the surface features in the liquid crystalline films. Therefore, it is assumed that the carrier‐transport properties of OFETs were enhanced by improving the molecular orientation in the liquid crystalline films. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)