A Better Perylene Suncatcher

Researchers in China have decorated the polycyclic aromatic hydrocarbon perylene with auxiliary groups to create the most efficient metal-free light-harvesting molecule reported to date for making dye-sensitized solar cells (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b01537). Perylene derivatives have been used extensively as photocatalysts and in organic light-emitting diodes, but they have not been very competitive against ruthenium and zinc organometallic complexes when it comes to solar cells. Perylene does hold an advantage in being less expensive than the metal complexes, and therefore researchers have been tweaking the molecule to improve its efficiency. Peng Wang of Changchun Institute of Applied Chemistry of the Chinese Academy of Sciences and coworkers tailored their N-annulated indenoperylene (red) with an ethynylbenzothiadiazolylbenzoic acid group (black) from scratch by using a combination of alkylation, cross-coupling, and other steps. Through a series of electrochemical and spectroscopy tests, the team determined that the new dye achieves a power conversion efficiency of 12.5%, which is on par with the best metal complexes. Both metal-containing and metal-free organic dyes are now being challenged by upstart perovskite light-harvesting materials.