Novel 4H-pyranylidene organic dyes for dye-sensitized solar cells: Effect of different heteroaromatic rings on the photovoltaic properties

Eight novel Ruthenium-free dyes consisting of a 4H-pyranylidene donor, a 2-cyanoacrylic acid acceptor and several heterocyclic rings with different electronic properties are designed and synthesized. The photovoltaic performances of the related dye-sensitized solar cells are discussed and compared, obtaining the best results with the thiophene followed by the mismatched-oriented thiazole. Dyes containing a pyrrol or a matched-oriented thiazole lead to the lower efficiencies of all the series. Charge extraction (CE) and transient photovoltage (TPV) measurements were conducted in order to investigate the recombination resistance and the difference in voltage for the devices. In order to get further insight in the electronic and optical properties of the studied compounds, theoretical calculations using TD-DFT and the CPCM have been carried out.