D-pi-A Structured Zn-II-Porphyrin Dyes with Thiophene Moiety for Highly Efficient Dye-Sensitized Solar Cells

Abstract

Herein, we design and synthesize a new D-pi-A zinc porphyrin, enveloped with a long alkyl thiophene unit (Th-ZnP-CNCOOH, TP), for dye-sensitized solar cells. The long alkyl-substituted thiophene unit is incorporated into the porphyrin dye to redshift its absorption wavelength. The effects of the alkyl thiophene moiety at the meso-position of the zinc porphyrin on the optical, electrochemical, and photovoltaic properties of the material are investigated. Dye-sensitized solar cells (DSSCs) prepared using the new dye, co-adsorbed with a simply structured organic co-adsorbent (HC-A4), are fabricated. The obtained TP/HC-A4-sensitized DSSCs exhibit a remarkable enhancement in both short-circuit current (J(SC)) and open-circuit voltage (V-OC), relative to the corresponding single-dye DSSCs, which can be attributed to a combination of the light-harvesting effect from their complementary absorption behavior and the slow charge-recombination process. The device based on TP/HC-A4 co-sensitization yields: J(SC)= 14.4 mAcm(-2), V-OC = 0.62 V, a fill factor FF= 0.75 and an efficiency eta = 6.7%. This performance is superior to those of devices containing either TP (eta = 2.4%) or HC-A4 (eta = 2.8 %), fabricated under the same conditions. The present study indicates that the prevention of dye aggregation, as well as complementary absorption spectra of the porphyrin dyes using co-sensitizers, are key to improving the device performance.