Synthesis and applications of novel acceptor–donor–acceptor organic dyes with dithienopyrrole- and fluorene-cores for dye-sensitized solar cells

Four novel symmetrical organic dyes (S1–S4) configured with acceptor–donor–acceptor (A–D–A) structures containing electron donating fluorene (S1 and S2) and N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1–S4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit current (JSC) of 12.27 mA/cm2, an open circuit voltage (VOC) of 0.61 V, a fill factor (FF) of 0.63, and an overall power conversion efficiency (η) of 4.73%. Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in its η value (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO2 surface and thus to increase the JSC value eventually.