Relationship between electrical properties and structure for modified poly(3-hexylthiophene) copolymer thin films

Relationship between the changing in structure and the electrical properties of modified poly(3-hexylthiophene) (P3HT) was examined. For modified P3HT two types of acceptor molecules including 1,4-Bis(5-brothien-2-yl)-2,3,5,6- tetrafluoro benzene (TFT) and 2,1,3-benzothiadiazole (Bz) were added into the main chain of P3HT. These modifications have the effect to molecular ordering of modified polymer thin film. The structural and optical characteristics of modified polymer were investigated by X-ray diffraction (XRD) and UV-visible absorption spectroscopy. By comparing to characteristic of pristine P3HT, the XRD pattern of modified polymer showed the shift of diffraction peak with decrease in intensity. These indicate that modified polymer chain reduced in structural coplanarity and crystallinity. Since the electrical property relates to the morphology and structure of thin film, the I-V characteristic of modified polymer thin film was measured with aluminum electrode and the results show the decrease in current relative to that in pristine P3HT. Furthermore, the mobility of modified polymer was also evaluated by using time of flight measurement with the structure of ITO/modified P3HT/Al at room temperature. The measured mobilities of modified is agree well with the I-V characteristics and this can demonstrate the effect of molecular ordering on its carrier conduction.