Tuning of spectral response in dye-sensitized solar cell by co-sensitization of black dye with small organic photosensitizers

A series of efficient donor- π -acceptor tiny organic dyes NA1, NA6, and NA7 were developed as co-sensitizers to improve the photovoltaic performance of the black dye-based dye-sensitized solar cells (DSCs). Dye aggregation on the TiO 2 surface was reduced, and improved sensitizer coverage was achieved through the introduction of a long alkoxy group in the donor part, the tuning of the anchoring parts, and the π -spacer of the co-sensitizer NA6. The spectral photoresponse was thereby dramatically improved across the spectrum from the ultraviolet to the visible range, and the recombination process was suppressed for the (black dye+NA6) co-sensitized cell compared with a single black dye. The co-sensitized black dye+NA6-based DSCs show a considerable increase in V oc (open-circuit voltage), J sc (short-circuit current density), and FF (fill factor) to 721 mV, 21.64 mAcm −2 and 0.733, respectively. A higher efficiency of 11.43% was, consequently, achieved for the (black dye+NA6) co-sensitized cell compared to 10.56% for the DSCs based on a single black dye.