Acridine-based metal-free organic dyes with various auxiliary acceptors for dye-sensitized solar cells

Two new metal-free organic dyes containing triphenylamine as a donor, acridine as a pi-bridge, cyanoacrylic acid as an anchoring group and a different auxiliary acceptor benzothiadiazole or N-propylbenzotriazole have been synthesized and used as sensitizers in dye-sensitized solar cells (DSSCs). The effect of auxiliary acceptors on the performance of the DSSCs was investigated by optical, electrochemical, theoretical, and photovoltaic methods. The DSSC based on BIM26 containing N-propylbenzotriazole shows power conversion efficiency (PCE) of 4.55%, much higher than that of BIM25 containing benzothiadiazole (3.76%) under simulated AM 1.5G solar irradiation. When co-adsorbed with CDCA, BIM25 exhibits a larger improvement in the photovoltaic performance (PCE = 5.59%) in comparison to BIM26 (PCE = 5.56%). The co-sensitization of BIM26 with a long absorption wavelength metal-free dye C1 further improves the PCE to 6.48%. These results demonstrate that the acridine based-dye with a N-propylbenzotriazole can be used not only as a single sensitizer to inhibit aggregation and charge recombination but also as a co-sensitizer to enhance light-harvesting ability.