Julolidine dyes with different acceptors and thiophene-conjugation bridge: Design, synthesis and their application in dye-sensitized solar cells

Four novel donor-π conjugated bridge-acceptor (D-π-A) metal-free organic dyes (J1, J2, J3 and J4) with a julolidine moiety as the electron donor for dye-sensitized solar cells (DSSCs) are synthesized. Their absorption spectra, electrochemical and photovoltaic properties were extensively investigated. Transient absorption spectra measurements show that insertion of one thiophene unit and replacing rhodanine-3-acetic acid by cyanoacetic acid can increase the dye regeneration process. Among these dyes, J3 gives the best photoelectric conversion efficiency of 1.52% with Jsc = 7.53 mA cm–2, Voc = 353 mV, FF = 0.57. Compared with those of J1, the Jsc and the conversion efficiency of solar cell based on J3 are significantly increased by the insertion of a thiophene unit.