Electronic structure and energy band gap of poly (9,9-dioctylfluorene) investigated by photoelectron spectroscopy

The electronic structure of poly (9,9-dioctylfluorene) (PFO) film on a Au-coated Si substrate was investigated by ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). From the UPS measurement, we obtained the ionization potential (Ip) of the PFO film, Ip = 5.60 +/- 0.05 eV. From the XPS shake-up peaks of the C1s core level, we estimated the electron energy band gap (E-g) of the film, E-g = 3.10 +/- 0.10 eV. By comparing the E-g with the optical absorption gap, we found that the value of E-g is closer to the optical absorption maximum than to the optical absorption edge. Therefore, we suggest that the optical absorption maximum may be a better approximation than the optical absorption edge in estimating E-g. (C) 2000 American Institute of Physics. [S0003-6951(00)00924-4].