Enhanced light-harvesting capability by phenothiazine in ruthenium sensitizers with superior photovoltaic performance

This paper reports on the design and synthesis of two new ruthenium dyes [Ru(dcbpy)(potip)(NCS)(2)] (JF-3, dcbpy 4,4'-dicarboxylic acid-2,2'-bipyridine, potip 2-(4-(10H-phenothiazin-10-yl)-5-octylthiophen- 2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline, and [Ru(dcbpy)(dpotip)(NCS)(2)] (JF-4, dpotip = 2-(4-(N,N-diphenylamino)-5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline) that contain electron-donating phenothiazine-based or N,N-diphenylamino-based ancillary ligands. The ruthenium dye JF-3, in which an excellent electron-donating phenothiazine is incorporated, shows superior DSC performance (9.1%; compared to 8.8% for N3). A comparison of the electron-donating phenothiazine and N, N-diphenylamino groups utilized in the molecular architecture of ruthenium dyes demonstrates that the phenothiazine group efficiently increases the molar extinction coefficient of band II and also broadens that band in the UV-vis absorption spectrum, reduces device resistance, increases electron lifetime, and enhances power-conversion efficiency. This finding not only clarifies the significance of multifunctionalized design in the molecular architecture of ruthenium dyes, but also represents an alternative route for the introduction of an excellent electron-donating group for improving the light-harvesting characteristics of ruthenium dyes as well as DSC performance.