A novel efficient metal free sensitizer containing asymmetric double donor-π-acceptor chains (DC) was synthesized for dye-sensitized solar cells (DSSCs). Comparing to 3.80%, 4.40% and 4.64% for the DSSCs based on the dyes with single chain (SC1, SC2) and cosensitizers (SC1 + SC2), the overall conversion efficiency reaches 6.06% for DC-sensitized solar cells as a result of its longer electron lifetime and higher incident monochromatic photon-to-current conversion efficiency.

Four novel D-p-A metal-free organic dyes DTP1-4 containing a dithienopyrrolobenzothiadiazole (DTPBT) unit were synthesized and applied in dye-sensitized solar cells, where DTPBT was employed as a p-spacer for the first time. The photophysical, electrochemical and photovoltaic properties of the dyes were systematically investigated. The dyes DTP1-4 showed broad absorption spectra and high molar extinction coefficient, resulting in high light harvesting efficiency. In addition, the impacts of donors and the thiophene unit as an additional p-spacer were also studied. The results showed that the dye DTP4 with triphenylamine as the donor exhibited better photovoltaic performance than DTP1-3 with phenothiazine as the donor. The linking position of the thiophene unit to the DTPBT unit significantly influenced the photovoltaic performance. A power conversion efficiency of 7.55% with 1 mM CDCA as the co-adsorbent under simulated AM 1.5 G illumination was reached by the DSSC sensitized by the dye DTP4. These results indicate that the DTPBT-based organic dye is a promising candidate for efficient DSSCs.

Double D–π–A branched organic dyes with a hexylene connector linked in different locations show diverse photovoltaic performances.

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