Variation of the donor and acceptor in D–A–π–A based cyanopyridine dyes and its effect on dye sensitized solar cells

Abstract

Two metal free organic dyes (TPCTh and TPCRh) with D–A–π–A configuration, having 3-cyanopyridine as an auxiliary acceptor and thiophene π-linkers along with a triphenylamine donor and cyanoacetic acid/rhodanine-3-acetic acid anchoring groups, were successfully synthesized and utilized as sensitizers in the fabrication of dye-sensitized solar cells (DSSCs). The opto-electronic properties of TPCTh and TPCRh were compared with the model sensitizer CCTh having carbazole as the donor and cyanoacetic acid as the anchoring group. Both the dyes showed red shifted absorption spectra compared to the standard CCTh dye. Also, TPCRh showed a broader absorption spectrum with a reduced band gap compared to TPCTh. However, theoretical studies indicate that the unavailability of excited state conjugation over the anchoring group could lead to restricted charge injection for the TPCRh dye, whereas the TPCTh dye exhibits complete conjugation over the entire molecule. The photovoltaic performance of the TPCTh dye was found to be better compared with the standard CCTh sensitizer as a result of better absorption contributed by the lower band gap in TPCTh leading to improved photon-light conversion and thus an improved J_sc of 11 mA cm⁻² over the 7.12 mA cm⁻² of CCTh. In addition, lifetime measurements corroborated a lower electron lifetime for TPCRh compared to TPCTh and CCTh.