A–D–A‐Type Oligothiophenes for Small Molecule Organic Solar Cells: Extending the π‐System by Introduction of Ring‐Locked Double Bonds

Abstract

A series of novel acceptor–donor–acceptor oligothiophenes terminally substituted with the 1‐(1,1‐dicyanomethylene)‐cyclohex‐2‐ene (DCC) acceptor has been synthesized. Structural, thermal, optoelectronic, and photovoltaic properties of the π‐extended DCC n Ts ( n = 1–4) are characterized and contrasted to the trends found for the series of parent dicyanovinyl (DCV)‐substituted oligothiophenes DCV n T. The optoelectronic properties reveal the influence of the additional exocyclic, sterically fixed double bonds in trans ‐configuration in the novel DCC n T derivatives. A close correspondence for derivatives with equal number of double bonds, that is, DCC n Ts and DCV( n + 1)Ts, is identified. Despite having the same energy gap, the energy levels of the frontier orbitals, HOMO and LUMO, for the DCC ‐ derivatives are raised and more destabilized due to the aromatization energy of a thiophene ring versus two exocyclic double bonds indicating improved donor and reduced acceptor strength. DCC‐terthiophenes give good photovoltaic performance as donor materials in vacuum‐processed solar cells (power conversion efficiencies ≤ 4.4%) clearly outperforming all comparable DCV4T derivatives.