Efficient improvements in the performance of Ru(II) π-expanded terpyridyl dyes in dye-sensitized solar cells: A theoretical study

To overcome the shortcomings of traditional Ru dyes in low molar extinction coefficient (epsilon) of the metal-to-ligand charge transfer band in the near-infrared region, we designed and studied two Ru dyes, HIS-2a and HIS-2b derived from HIS-2. The intrinsic causes for varying short-circuit photocurrent density (J(sc)) and open-circuit photovoltage (V-oc) have been systematically investigated on the dyes and dye/(TiO2)(38) systems including the conduction band energy shift, electronic structures, light harvesting efficiency, electron injection driving force, electronic coupling, dye regeneration driving force and so on. Those results suggest that, compared with HIS-2 and HIS-2b, HIS-2a has red-shifted absorption spectrum and increased transition intensity in NIR region, which would lead to a larger J(sc). At the same time, the conduction band energy of HIS-2a shifts little compared with other dyes, which will not have much effect on V-oc Hence, we could speculate that HIS-2a is a promising candidate with enhanced J(sc) and a more efficient Ru(II) pi-expanded terpyridyl dye. We also hope that this study will provide theoretical guidelines for the synthesis of new Ru dyes. (C) 2015 Elsevier B.V. All rights reserved.