Influence of different acceptor groups in julolidine-based organic dye-sensitized solar cells

• Two julolidine dyes with different accepters are applied in dye-sensitized solar cells.
• Transient absorption measurements show that both dyes are quickly regenerated.
• Voc and η increase 25%–30% by replacing rhodanine-3-acetic acid to cyanoacetic acid.

Two novel organic dyes containing julolidine as the electron donor and cyanoacetic acid or rhodanine-3-acetic acid as the electron acceptor bridged by bithiophene unit were synthesized. The absorption spectra, electrochemical and photovoltaic properties of the new dyes were extensively investigated. Transient absorption spectra measurements show that both sensitizers are quickly regenerated and the dye cations are efficiently intercepted by the redox mediator. The overall conversion efficiencies of 2.6% and 2.0% were obtained for dye-sensitized solar cells (DSSC) based on the cyanoacetic acid and rhodanine derived dyes, respectively. Compared with the rhodanine terminated dye, the open circuit voltage and the conversion efficiency of solar cell based on the cyanoacetic acid dye are increased about 25% and 30%, respectively. The lower efficiency of solar cell based on rhodanine is mainly resulted from the broken delocalization of the excited state due to the NCH2CO2H anchor, which affects the electron injection from the rhodanine terminated dye to the conduction band of TiO2.