Complementary Absorption versus Morphology in All-Conjugated Block Copolymer Solar Cells

An efficient and simple method for synthesizing all-conjugated diblock copolymers is reported, using the Stille polycondensation of A-A (dithienosilole) and B-B (diketopyrrolopyrrole) monomers with a macro end-capping agent P3HT. Diblock and triblock copolymers were produced with a molar composition that was tuned via the macromonomer molar mass and feed ratio. The molar mass and topology of the macromolecules obtained are discussed on the basis of the Carothers equation, conversion, and monomer ratio. Spectrophotometry and cyclic voltammetry were used to highlight the complementarity of block absorption and the donor-acceptor nature of copolymers. Finally, integration in solar cells has been successfully performed with efficiencies reaching 2%. Performances of the devices were molar composition dependent and revealed that the performance enhancement provided by low-band-gap block absorption was balanced by the copolymer nanostructuration that shrinks the charge collection at electrodes.