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 $I_p\text{=5.80\hspace{0.17em}}\mathrm{eV}$ and $E_a\text{=2.12\hspace{0.17em}}\mathrm{eV}.$ 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.