Renaissance of Fused Porphyrins: Substituted Methylene-Bridged Thiophene-Fused Strategy for High-Performance Dye-Sensitized Solar Cells

Over the last decades, porphyrin sensitizers have made a remarkable contribution to performance improvement in dye-sensitized solar cells (DSSCs). In particular, versatile push pull-type porphyrin sensitizers have achieved power conversion efficiencies (eta) over 10% as a result of their improved light-harvesting abilities. Meanwhile, aromatic ring fusion to a porphyrin core is an attractive option for highly efficient DSSCs because of its expanded pi-conjugation and resultant red-shifted absorption. Nevertheless, aromatic-fused porphyrin sensitizers have suffered rather low cell performances due to their mismatch of HOMO-LUMO levels, high aggregation tendency, and short lifetime of the excited states. Bearing these in mind, we envisioned that the fusion of substituted methylene-bridged small aromatic ring to a porphyrin core would overcome these drawbacks, boosting the cell performance. Herein, we report a series of substituted methylene-bridged thiophene-fused porphyrins, AfZnP, DfZnP, and DfZnP-iPr. After optimization, DSSC with the donor-side thiophene-fused DfZnP-iPr achieved an eta-value of 10.1%, which is comparable to that of DSSC with GYSO (10.0%), a representative high-performance push-pull-type porphyrin sensitizer. More importantly, cosensitization of DfZnP-iPr with a complementary sensitizer LEG4 further led to an eta-value of 10.7%, which is the highest value ever reported for DSSCs with fused porphyrin sensitizers. Therefore, our strategy will reboot the exploration of aromatic fused porphyrin sensitizers for high-performance DSSCs.