Novel D-A-π-A coumarin dyes containing low band-gap chromophores for dye-sensitised solar cells

Coumarin dyes containing a low band-gap chromophore of benzothiadiazole, which comprises a coumarin moiety as the electron donor and a cyanoacrylic acid moiety as electron acceptor in D-A-pi-A system, were developed to use in dye-sensitised solar cells (DSSCs). The introduction of the benzothiadiazole unit into the molecular framve distinctly narrowed the band-gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), so that the absorption peak was red-shifted. As a result, a solar cell based on the HKK-CM4 sensitiser showed better photovoltaic performance with a J(SC) of 14.3 mA cm(-2), a V-OC of 0.58 V, and an FF of 0.72, corresponding to an overall conversion efficiency eta of 5.97% under standard AM 1.5 irradiation. (C) 2012 Elsevier Ltd. All rights reserved.