Toward a Rational Design of Poly(2,7-Carbazole) Derivatives for Solar Cells

On the basis of theoretical models and calculations, several alternating polymeric structures
have been investigated to develop optimized poly(2,7-carbazole) derivatives for solar cell applications.
Selected low band gap alternating copolymers have been obtained via a Suzuki coupling reaction. A good
correlation between DFT theoretical calculations performed on model compounds and the experimental
HOMO, LUMO, and band gap energies of the corresponding polymers has been obtained. This study
reveals that the alternating copolymer HOMO energy level is mainly fixed by the carbazole moiety, whereas
the LUMO energy level is mainly related to the nature of the electron-withdrawing comonomer. However,
solar cell performances are not solely driven by the energy levels of the materials. Clearly, the molecular
weight and the overall organization of the polymers are other important key parameters to consider when
developing new polymers for solar cells. Preliminary measurements have revealed hole mobilities of about
1 × 10-3 cm2·V-1·s-1 and a power conversion efficiency (PCE) up to 3.6%. Further improvements are
anticipated through a rational design of new symmetric low band gap poly(2,7-carbazole) derivatives.