Tuning the Photovoltaic Performance of Benzocarbazole-Based Sensitizers for Dye-Sensitized Solar Cells: A Joint Experimental and Theoretical Study of the Influence of π-Spacers

Tuning the parameters to enhance the efficiencies of a novel set of metal free sensitizers for dye sensitized solar cells (DSSC) is carried out by varying the pi-conjugated spacers that link the donor benzocarbazole to the acceptor cyanoacrylic acid. The molecules are synthesized by different combinations of spacers, namely fluorene-thiophene (BET), fluorene-furan (BEE), fluorene-phenyl (BFB), and thiophene-phenyl (BTB). The molar extinction coefficients of all the dyes are high which is attributed to benzocarbazole, but it is higher in the dyes in which fluorene is one of the spacers. But interestingly, in the photovoltaic device when the non-fluorene dye BTB is the sensitizer, red-shifted and broader incident photon-to-current efficiency (IPCE) curves are obtained leading to larger short circuit current density, J(sc), almost double when compared to BFB-based cell. The efficiency of the device with this dye as the sensitizer is also the highest in this series. The reasons behind these observations are investigated using computational techniques.