Synthesis of double D-A branched organic dyes employing indole and phenoxazine as donors for efficient DSSCs

Four novel metal-free organic sensitizers bearing double donor-acceptor (D-A) branches with indole and phenoxazine units as donors (SDD1-4) and cyanoacrylic acid as electron acceptor were synthesized and characterized for dye-sensitized solar cells (DSSCs). Dyes SDD1-3 were designed with indole as a donor and 1,4-phenylenebis(methylene), 1,4-butylene and 1,6-hexylene as a linker, respectively, while the dye SDD4 was designed with phenoxazine as a core donor. Their photophysical, electrochemical, and DSSCs characteristics were investigated. The results show that the architecture structure of the linkage affects the performance of the cells slightly. The DSSCs based on SDD4 shows much higher η than the DSSCs based on SDD1-3, which indicated that phenoxazine is a better donor than indole. Under standard global AM 1.5 solar condition (100 mW cm−2), the SDD4 dye-sensitized cell gave the highest η of 4.33% with chenodeoxycholic acid as a coadsorbent, reaching 82% of N719-based DSSCs.

175Comparing to the dye RD with a single D-A unit, the dye SDD4 with phenoxazine as donor shows better photovoltaic performance due to its two D-A light-harvesting units and two anchoring groups.