New dual donor-acceptor (2D-π-2A) porphyrin sensitizers for stable and cost-effective dye-sensitized solar cells

Abstract

A series of porphyrin sensitizers that featured two electron-donating groups and dual anchoring groups that were connected through a porphine π-bridging unit have been synthesized and successfully applied in dye-sensitized solar cells (DSSCs). The presence of electron-donating groups had a significant influence on their spectroscopic, electrochemical, and photovoltaic properties. Overall, the dual anchoring groups gave tunable electronic properties and stronger attachment to TiO2 . These new dyes were readily synthesized in a minimum number of steps in gram-scale quantities. Optical and electrochemical data confirmed the advantages of these dyes for use as sensitizers in DSSCs. Porphyrins with electron-donating amino moieties provided improved charge separation and better charge-injection efficiencies for the studied dual-push-pull dyes. Attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy of the porphyrin dyes on TiO2 suggest that both p-carboxyphenyl groups are attached onto TiO2, thereby resulting in strong attachment. Among these dyes, cis-Zn2BC2A, with two electron-donating 3,6-ditertbutyl-phenyl-carbazole groups and dual-anchoring p-carboxyphenyl groups, showed the highest efficiency of 4.07 %, with J(SC)=9.81 mA cm(-2), V(OC)=0.63 V, and FF=66 %. Our results also indicated a better photostability of the studied dual-anchored sensitizers compared to their mono-anchored analogues under identical conditions. These results provide insight into the developments of a new generation of high-efficiency and thermally stable porphyrin sensitizers.

Keywords: donor-acceptor systems; dyes/pigments; porphyrins; sensitizers; solar cells.