D–π–A Structured ZnII‐Porphyrin Dyes with Thiophene Moiety for Highly Efficient Dye‐Sensitized Solar Cells

Herein, we design and synthesize a new D–π–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 red‐shift 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 (JSC) and open‐circuit voltage (VOC), 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: JSC=14.4 mA cm−2, VOC=0.62 V, a fill factor FF=0.75 and an efficiency η=6.7 %. This performance is superior to those of devices containing either TP (η=2.4 %) or HC‐A4 (η=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. A dye that does it! Zinc porphyrins enveloped with long alkyl thiophene units and a simply structured organic co‐adsorbent are presented. Dye‐sensitized solar cells prepared using this new dye show an enhanced performance.