Predicting properties of organic optoelectronic materials: Asymptotically corrected density functional study

A practical computational procedure has been proposed that provides key electronic parameters of a polymer (fundamental bandgap, ionization energy, electron affinity, and intrachain electron and hole mobilities) determining its suitability as a donor or acceptor in organic optoelectronic materials. Series of oligomer calculations at the Becke3-Lee-Yang-Parr level with and without a self-contained asymptotic correction using the 6-31G* basis set were performed. The bandgap, ionization energy, and electron affinities of a polymer are extrapolated from those of its oligomers obtained from the highest occupied and lowest unoccupied orbital energies in the Koopmans-like approximation. This scheme has been applied to conjugated polymers having the poly(p-phenylene), poly(thiophene), or poly(pyrrole) backbone as well as to PCBM. The observed values of the electronic parameters have been reproduced within less than 1 eV in most cases. With the predicted values of these parameters, estimates of the open-circuit voltage and drift potential have been made for 22 valid donor-acceptor combinations. Several potentially useful combinations have been identified including the poly(thiophene):PCBM. The electron and hole mobilities have been found to correlate more strongly with the conformation (planarity) than the bandgap, but otherwise do not differ significantly.