Abstract
In this study, we report on the formation of blend-film organic field effect transistors of two p-type semiconductors of pentacene (PTC) and antradithiophene (ADT) that have similar structure and carrier transport properties. We co-deposited ADT/PTC blend films of various mixing ratio and used X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD) to characterize the thin-film composition, morphology, grain size, and crystallinity. Afterwards, we fabricated blend-film OFETs, measured their electrical properties, and evaluated their air stability. And finally, we investigated the relationship between the degree of oxidation and air stability of the blend films. From the XRD patterns, we concluded that the ADT/PTC blend films were of mixing origin not phase separated, as evidenced by the formation of the new diffraction peaks. We also found that the higher PTC proportion in the blend film would form a structure with larger d-spacing. This fact might enhance the aromatic ring overlap area and increased the intermolecular hole transport. In AFM image data, we found that the blend films with the small percentage of ADT had the larger grain size than the PTC thin film, suggesting a larger lateral growth. For the blend-film OFETs, we found that the device of a mixing ratio of the 90%PTC had the hole transport mobility of 0.37 cm2V-1s-1, comparable to the PTC device of 0.44. The device of a mixing ratio of the 90%PTC was more stable than the PTC device in ambient condition. After 900 times cycle test, or 3 months shelf-life test, the mobility of 0.3 cm2V-1s-1 and 0.1 cm2V-1s-1 was still maintained, respectively. In comparison, the PTC device dropped to 0.2 cm2V-1s-1 and 0.008 cm2V-1s-1 after the same treatment. In the oxidation experiment results, we also found that the blend films with small percentage of ADT were less easily oxidized than PTC thin film.