Scharber et al. proposed an efficiency model for organic photovoltaic cells based on the orbital energies of the monomers of the donor- and acceptor- polymers [Advanced Materials 18 (2006) 789â€“794]. We report theoretical extensions of this approach. First, the frontier-orbital energies and electronic spectra of n-length oligomers (n = 1 âˆ’ 5) of 3-butylthiophene have been determined. The results show reasonable convergence with respect to system size at the point of a trimer with alkyl end caps. The HOMO-LUMO gap well matches computed excitation energies. Second, the structures and electronic spectra of dimers formed by three different monomers, with various linkages were determined. The electronic spectra of the dimers was computed as a function of the dihedral angle between the monomers to explore the response to geometrical distortion. Finally, for each of the top 21 monomer candidates provided by the Harvard Clean Energy Project, we have computed the excitation spectrum and constructed a frequency- dependent external quantum efficiency function. Inclusion of this additional information into the efficiency model gives a broad range of results. Further experiments are needed to determine if this straightforward extension of Scharberâ€™s model is worth the additional computational expense in the quest for practical, efficient donor-polymers.
Journal of Undergraduate Chemistry Research
Lahm, Mitchell E.; Niblock, Megan M.; Migliore, John M.; Mckenzie, Kendra M.; Lüthi, Hans P.; and King, Rollin A., "Computational Analysis Beyond the Monomer Frontier Orbitals for Photovoltaic Donor-Polymer Candidates" (2021). Chemistry Faculty Publications. 31.