Titanyl Phthalocyanine (TiOPc) Organic Thin Film Transistors with Highly pi-pi Interaction

Abstract

The objective of this research is to obtain uniform vacuum-deposition triclinic phase II crystal of titanyl phthalocyanine (alpha-TiOPc) films from various TiOPc crystal forms. The crystal structure and morphology of vacuum-deposited TiOPc films can be manipulated by deposition rate and substrate temperature. Crystal structure was determined by X-ray diffraction (XRD). Thin film morphology was analyzed by scanning electron microscope (SEM). Highly ordered alpha-TiOPc film with an edge-on molecular orientation was deposited on octadecyltrichlorosilane (OTS) treated Si/SiO2 surface. All TiOPc crystal forms, such as amorphous, alpha and gamma phases, provided the triclinic phase II crystal of TiOPc. The full width at half maximum (FWHM) of the peak at 7.5 degree in XRD spectra was 0.23, 0.27 and 0.29 for gamma, alpha and amorphous powder when substrate temperature maintained at 180 degrees C, respectively. The FWHM of the 7.5 degree peak can be achieved 0.22 deposited from all crystal forms at elevated temperature higher than 220 degrees C. The alpha-TiOPc deposition film exhibited an excellent p-type semiconducting behavior in air with dense packing structure due to the close pi-pi molecular packing. The devices, field-effect mobility range from 0.02 to 0.26 cm(2)/V s depending on various process parameters. The on/off current ratio (I-on/I-off) is over 10(5). The TiOPc OTFTs will be applied as multi-parameter gas sensor in the near future.