Direct Measurement of Conjugated Polymer Electronic Excitation Energies Using Metal/Polymer/Metal Structures

We report electroabsorption measurements of built-in electric fields and internal photoemission measurements of Schottky barriers to determine the charge transfer and single-particle energy gaps of the conjugated polymer poly[2-methoxy, 5-(2\ensuremath{'}-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). For MEH-PPV, with an exciton absorption peak of 2.25 eV, or results yield a single-particle energy gap of 2.45 eV and a charge transfer energy gap of at least 2.35 eV. Therefore the exciton binding energy is 0.2 eV and the bipolaron binding energy is less than 0.1 eV.