On the reliability of determination of energies of HOMO levels in organic semiconducting polymers from electrochemical measurements

摘要

Reliability of determination of energies of HOMO levels in semiconducting polymers by the cyclic vol-tammetry (CV) is assessed. Ionization energies (I_c) as determined by the UV photoelectron spectroscopy (UPS) reported in the literature for 33 polymers are correlated with their oxidation potentials (π_(ox)) as determined by CV. It is demonstrated that the resulting correlation does not obey the equation commonly used to derive the HOMO energies from the electrochemical measurements. The equation, best describing the obtained correlation, may be written as I_c = (1.7±0.2) × (eπ_(ox)) + (4.6±0.1) eV. It should be noted that the slope of the correlation is much higher than the slope of an analogous correlation determined for small-molecule organic semiconductors. The accuracy of estimation of the energies of HOMO levels from CV experiments is of the order of 0.1 eV at the best.