•Direct linkage of an oligothiophenes spacer to the nitrogen atom of a donor amine.•Linkage of donor–acceptor bridge through an elongated oligothiophene π-spacer.•Enhancement of spectral response when compared with a fewer thiophene analogue.•Compatibility of new sensitizer with versatile electrolyte systems such as cobalt.Through the embodiment of direct linkage of oligothiophenes to the nitrogen atom of a donor amine in the bridged donor–acceptor module, a novel and efficient organic sensitizer (AG3) has been designed, synthesized and applied in dye-sensitized solar cells. AG3 contained an electron donating (diphenylamine) and an electron accepting (cyanoacrylic acid) functionality linked through an elongated oligothiophene π-spacer. The target sensitizer was successfully synthesized, found to be highly soluble in common organic solvents, showed intense spectral response when compared with fewer thiophene analogue, and afforded 5.9%, 4.3% and 5.2% solar-to-energy conversion efficiencies with solvent-based, ionic liquid and cobalt-mediated electrolytes, respectively, when tested under irradiation of 100 mW cm−2 air mass 1.5 global (AM1.5G) sunlight.

A novel, solution-processable small molecular electron acceptor (HP1) based on diketopyrrolopyrrole and naphthalenediimide fragments was designed and synthesized via a Stille coupling reaction, characterized by spectroscopic means, and exhibited excellent solubility and thermal stability. HP1 exerted strong and very broad absorption tailing into the near infra-red region, with appropriate energy levels matching with the archetypal electron donor, poly(3-hexylthiophene) (P3HT), and afforded 1.02% power conversion efficiency with a high open-circuit voltage (1.05 V) when tested in solution-processable bulk-heterojunction devices.