ELECTROCHEMICAL DETERMINATION OF THE IONIZATION-POTENTIAL AND ELECTRON-AFFINITY OF POLY(9,9-DIOCTYLFLUORENE)

We report cyclic voltammetry measurements for the blue electroluminesc ent conjugated polymer poly(9,9-dioctylfluorene). Both oxidation and r eduction potentials are determined and thus estimates of both the ioni zation potential I-p and electron affinity E-a of the polymer are obta ined for the same sample under the same experimental conditions. We es timate I-p = 5.80 eV and E-a = 2.12 eV. These results disagree with th e common assumption that E-a is, to good approximation, given by the d ifference between I-p and the optical gap. Measurements on indium tin oxide/polyfluorene/calcium light emitting diode structures are consist ent with the deductions from the electrochemical data. (C) 1998 Americ an Institute of Physics. [S0003-6951(98)00843-2].