The effects of electron-acceptor strength and donor-to-acceptor ratio on the electronic properties of thieno[3,2-b]thiophene-based donor–acceptor copolymers

Abstract

Theoretical analysis on the geometries and electronic properties of thieno[3,2-b]thiophene (TT)-based alternating donor–acceptor conjugated polymers of donor and acceptor unit with the ratio of 1:1 and 2:1, as well as their corresponding monomers, is reported. The theoretical results suggest that both the electron-acceptor strength and the mole ratio of donor to acceptor (D/A ratio) contribute significantly to the electronic properties of alternating donor–acceptor conjugated copolymers. However, the impact of D/A ratio on the geometrical and electronic properties of the donor–acceptor copolymers is more marked compared with that of the acceptor strength. The increase in the portion of TT unit can significantly decrease the bond length alternation, strengthen the π-electron delocalisation and narrow the band gap. In addition, the mole ratio of donor-to-acceptor unit also has an impact on the bandwidth. The copolymers possessing a D/A ratio of 2:1, i.e. p-TTP-DTT, p-DTP-DTT and p-TBT-DTT, may be good candidates for conduction materials due to their very narrow band gap ( < 0.72 eV), relatively small effective mass of carriers and relatively large bandwidth.

Keywords::

• thieno[3,2-b]thiophene
• donor-to-acceptor ratio
• electron-acceptor strength
• electronic properties

Acknowledgements

This work was supported by Science and Technology Foundation of Chongqing Municipal Education Commission (Grant No. KJ131102) and National Natural Science Foundation of China (Grant No. 21073144).