Electrochemical Considerations for Determining Absolute Frontier Orbital Energy Levels of Conjugated Polymers for Solar Cell Applications

Narrow bandgap conjugated polymers in combination with fullerene acceptors are under intense investigation in the field of organic photovoltaics (OPVs). The open circuit voltage, and thereby the power conversion efficiency, of the devices is related to the offset of the frontier orbital energy levels of the donor and acceptor components,1, 2 which are widely determined by cyclic voltammetry. Inconsistencies have appeared in the use of the ferrocenium/ferrocene (Fc+/Fc) redox couple, as well as the values used for the absolute potentials of standard electrodes, which can complicate the comparison of materials properties and determination of structure/property relationships. Electrochemical measurements are routinely used to determine the orbital energy levels of donor and acceptor materials under investigation for the fabrication of organic solar cells. There are, however, inconsistencies in the use of standard redox couples and the absolute potential of standard electrodes, which complicate comparison of materials properties and determination of structure/property relationships.