Thieno[3,2-b]thiophene-diketopyrrolopyrrole containing polymers for inverted solar cells devices with high short circuit currents

The synthesis and characterization four diketopyrrolopyrrole containing conjugated polymers for use in organic photovoltaics is presented. Excellent energy level control is demonstrated through heteroatomic substitution whilst maintaining similar solid state properties as shown by X-ray diffraction and atomic force microscopy. Inverted solar cells were fabricated with the best devices having short circuit currents exceeding 16 mA cm^-2 and efficiencies of over 5% irrespective of whether [6,6]-phenyl-C ₆₁-butyric acid methyl ester (PC₆₀BM) or [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM) is used. Transient absorption spectroscopy on the bulk heterojunction blends shows efficient charge photo-generation, with the variations in short circuit current correlated to the energetic offset between polymer and fullerene. Four diketopyrrolopyrrole containing polymers are synthesized and evaluated for use in organic solar cells. Heteroatomic substitution allows precise control over the polymer energy levels with minimal disruption to the solid state properties. Variations in the short circuit current are linked to the energetic offset between polymer and fullerene.