X-ray photoemission spectroscopy and Fourier transform infrared characterizations of C60 states in C60 doped conducting polymers

Conducting polymer polythiophene (PT) film incorporated with ${\mathrm{C}}_{60}$ was prepared by electrochemical doping and diffusing injection methods. Charge transfer and the molecule-chain interaction were investigated by x-ray photoemission spectroscopy (XPS). Vibration states of the doped ${\mathrm{C}}_{60}$ and polymer backbone in the hybrid films were also investigated by fourier transform infrared (FTIR) reflaction absorption spectroscopy and FTIR transmission. The XPS spectral profile of the electrochemically doped sample was different from that of the casting sample, which reflects the different dopant-chain interactions in polymer films. The higher binding peaks appearing in the C $1s$ spectra correspond to ${\mathrm{C}}_{60}$ and its charged states doped in the polymer, which are closely connected with threefold $t_{1u}$ lowest unoccupied molecular orbital and fivefold $h_u$ higest occupied molecular orbital. FTIR transmission measurements clarified that ${\mathrm{C}}_{60}$ molecules were doped in the polymer film using both electrochemical doping and casting, as characteristic peaks due to the vibration modes of ${\mathrm{C}}_{60}$ were observed. The ${\mathrm{C}}_{60}$ peaks observed in the spectra for electrochemical doping and casting samples differed, which reflects the different doping states of ${\mathrm{C}}_{60}$ . The results of XPS and FTIR suggest the conductive state of PT may be controlled by changing the ionic states of ${\mathrm{C}}_{60}$ .