Anthracene-Bridged Sensitizers for Dye-Sensitized Solar Cells with 37% Efficiency under Dim Light

New anthracene-bridged organic dyes CXC12 and CXC22 are designed and synthesized for high-efficiency dye-sensitized solar cells (DSSCs) under dim light. Compared to their parent dye TY6, CXC dyes have additional anthracene-acetylene group to extend the pi-conjugation of the molecules, resulting in red-shifted absorption and an enhanced molar extinction coefficient. The absorption spectra of CXC12 and CXC22 with a maximum located at 561 and 487 nm, respectively, match to those of AM 1.5G sunlight and T5 fluorescent light better than that of TY6 (419 nm). It was initially anticipated that long alkoxyl chains introduced to the 2,6-position of the bridged anthracenyl in CXC12 will retard charge recombination and dye molecular aggregation, and achieve a higher device open-circuit voltage. However, adsorption of CXC12 molecules on the photoanode dramatically decrease to less than half as compared to that of CXC22 and TY6, resulting in lower short-circuit current and thus power conversion efficiency. Among these three anthracene-based dyes, CXC22 has the most appropriate molecular structure for light harvesting and striking the balance between dye loading and molecular aggregation, to exhibit a remarkable power conversion efficiency as high as 37.07% under dim-light. Therefore, this work shows the potential of anthracene-bridged organic dyes for indoor photovoltaic applications.