Electrochemical determination of the ionization potential and electron affinity of poly(9,9-dioctylfluorene)

We report cyclic voltammetry measurements for the blue electroluminescent conjugated polymer poly(9,9-dioctylfluorene). Both oxidation and reduction potentials are determined and thus estimates of both the ionization potential I-p and electron affinity E-a of the polymer are obtained for the same sample under the same experimental conditions. We estimate I-p = 5.80 eV and E-a = 2.12 eV. These results disagree with the common assumption that E-a is, to good approximation, given by the difference between I-p and the optical gap. Measurements on indium tin oxide/polyfluorene/calcium light emitting diode structures are consistent with the deductions from the electrochemical data. (C) 1998 American Institute of Physics. [S0003-6951(98)00843-2].