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Keywords:

  • conjugated polymers;
  • inverted solar cells;
  • thienothiophene

Abstract

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-C61-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.