How accurate are energies of HOMO and LUMO levels in small-molecule organic semiconductors determined from cyclic voltammetry or optical spectroscopy?

摘要

Highlights?Accuracy of determination of HOMO and LUMO energies by indirect methods was assessed.?Literature data show that electrochemical gap is lower than transport gap by ca. 16%.?Optical gap is lower than transport gap by ca. 37%.?The accuracy can be improved by use of correction factors.AbstractExamined are relations between the energies of the transport gaps (i.e., the gaps determined by UPS/IPES measurements and taken for ‘true’ HOMO-LUMO gaps), and the electrochemical gaps (determined from CV experiments) and optical gaps (determined from UV-VIS optical spectroscopy). The statistics, based on literature data for several small (non-polymeric) molecules, shows that, on average, the electrochemical measurements underestimate the gap energies by ca. 16%, and the optical gap is smaller than the transport gap by ca. 37%. These differences seriously affect the accuracy of determination of energies of HOMO and LUMO levels by indirect methods. The concordance with the results obtained from the UPS/IPES measurements can be improved by using correction factors put forward in the present paper.]]>