Polymers with Alkylsulfanyl Side Chains for Bulk Heterojunction Solar Cells: Toward a Greener Strategy

The synthesis and properties of three co-polymers obtained through a Knoevenagel poly-condensation are reported. They are soluble in organic solvents, filmable and solvatochromic. They are characterized through GPC, NMR and UV-visible spectroscopies, CV, and AFM. They display some proneness to form π-stacks, broad absorptions up to about 700 nm, HOMO and LUMO energies that fit those of [60]PCBM. The polymers are incorporated in blends with PCBM within BHJ devices. The best results are found for PSCs obtained from P1 (2.7 % PCE). The insertion of alkylsulfanyl chains improves the photovoltaic performances, with respect to those of alkyl-substituted analogous polymers. The Jsc of the devices are greatly enhanced, supporting the employment of (alkylsulfanyl)thienyl units as base units in photoactive materials.