Optical properties of Thienylfuran linear oligomers*

Thiophene oligomers are promising for photovoltaics due to stability and strong absorption in the visible region. A recent proposal is co-polymerization with furan units, building linear thienylfuran oligomers[1]. We present a theoretical study of thiophene, furan and thienylfuran short chains, using different methodologies - from Hartree-Fock HF and Density Functional Theory DFT, to Moller-Plesset perturbation HF-MP2, many-body perturbation G0W0@DFT and Bethe-Salpeter Equation[2-4]. We investigate monomers T and F up to linear tetramers with different sequencing of units TT, TF or FF. For any TT sequencing we find a torsion angle of 150°, while all others result planar. Interestingly, we find that the first optical transitions start from ∼4 eV for dimers and reach a promising threshold of ∼3 eV for the tetramers, at this point with ionization potentials of ∼7 eV. Regarding the conduction band minimum of  ∼4.2 eV for much used semiconducting oxides, this can lead to efficient photovoltaic charge-transfer in real applications.

[1]O. Gidron et al., Chem. Commun., 49, 6256 (2013); [2]M. Valiev et al., Comput. Phys. Commun., 181, 1477 (2010); [3]V. Blum et al., Comput. Phys. Commun., 180, 2175 (2009); [4]M. Pinheiro Jr et al., Phys. Rev. B, 92, 195134 (2015).