Optical properties of donor–acceptor conjugated copolymers: A computational study

Highlights: • The optical properties of 12 donor/acceptor copolymers are predicted using TDDFT. • A full rationalization with respect to the nature of the D/A pair is provided. • The CPDTDPP polymer exhibits the highest light harvesting properties. • The stabilized LUMO of CPDTDPP with respect to PCBM limits its potential for OPV. • CPDTBT emerges as a better compromise for solar cell applications. TDDFT calculations are associated to an extrapolation scheme to predict the optical properties of twelve donor-acceptor copolymers, in which carbazole, benzodithiophene or cyclopentadithiophene donor subunits are combined to benzofurazane, benzothiadiazole or diketopyrrolopyrrole acceptor moieties. Relative excitation energies and absorption strengths are rationalized in terms of geometrical, electronic and optical descriptors. It is shown that the combination of a cyclopentadithiophene with a diketopyrrolopyrrole leads to the lowest excitation energy and highest light absorption efficiency within the series. However, combining cyclopentadithiophene and benzodithiophene subunits appears as more efficient for solar cell applications due to better energy level alignment with respect to PCBM.