New D-A-D-A-D push–pull organic semiconductors with different benzo[1,2-b:4, 5-b′] dithiophene cores for solution processed bulk heterojunction solar cells

Abstract

The synthesis and characterization of two D–A–D–A–D push–pull organic semiconductors based on either bis- (2-ethylhexyloxy) benzo [1,2-b:4,5-b′] dithiophene or bis- (triisopropylsilylethynyl) benzodithiophene electron rich core are described. The optical and electrochemical properties of these compounds indicate that these materials can absorb sunlight over a wide spectral range from 350 to 700 nm and exhibit suitable energy levels for efficient exciton dissociation. These small molecules were used as donor coupled with phenyl-C71-butyric acid methyl ester acceptor for the fabrication of solution processed small molecule bulk heterojunction solar cells. The rigid and -conjugation of the silylacetylene substituted analog π-extended compared to the hexyloxy substituted analog facilitates intermolecular packing interactions of small π–π charge transfer and intermolecular molecule which induce a deep HOMO level, producing a high open circuit voltage of ∼0.98 V. The achieved PCE was 5.69% when the active layer hexyloxy analog: phenyl-C71-butyric acid methyl ester was processed with optimized 1-chloronaphathalene additive.