Enhanced Donor-π-Acceptor Character of a Porphyrin Dye Incorporating Naphthobisthiadiazole for Efficient Near-Infrared Light Absorption

Donor--acceptor (D--A) molecules play an important role in various fields including polymer solar cells (PSCs) and dye-sensitized solar cells (DSSCs). In PSCs, naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole (NTz) has emerged as a promising acceptor owing to its higher electron-accepting ability compared with 2,1,3-benzothiadiazole (BT), which is a widely used acceptor unit in DSSCs as well as PSCs. On the other hand, various D--A-type porphyrin dyes have been developed for use in DSSCs and have achieved high power conversion efficiencies (). Given that enhanced D--A character improves light-harvesting ability in the near-infrared (NIR) region, we have designed and synthesized for the first time a novel D--A-type porphyrin sensitizer, ZnPNTz, incorporating the NTz unit. The porphyrin ZnPNTz shows excellent absorption in the NIR region together with a large Stokes shift as a result of the NTz moiety. A DSSC fabricated with ZnPNTz exhibits photocurrent generation at wavelengths up to 860 nm. Therefore, we have demonstrated that the NTz unit is a promising electron-acceptor unit for novel D--A small molecules exhibiting unique optical properties in the NIR region.