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

Abstract

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 (Eg) of the film, Eg=3.10±0.10 eV. By comparing the Eg with the optical absorption gap, we found that the value of Eg 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 Eg.