Umbrella-Shaped m-Terphenyls for Highly π-Extended Planar Dyes toward High-Performance Dye-Sensitized Solar Cells

Porphyrin dyes with pi-extended structures, particularly those with aromatic fused designs, have garnered considerable attention as efficient sensitizers for dye-sensitized solar cells (DCCSs). However, their photovoltaic performance has often been limited due to high aggregation tendencies caused by strong pi-pi interactions and charge recombination processes. Since m-terphenyls can be used as effective sterically protecting groups, the incorporation of umbrella-shaped m-terphenyls on the top of porphyrin dyes could provide an effective approach to unlock the full potential of highly pi-extended porphyrin dyes. In this study, we report new fused porphyrin dyes, T-Ph, T- t BuPh, TT-Ph, and TT- t BuPh, introducing m-terphenyl groups. This innovative design ensures both blocking effects on dye aggregation on TiO2 and charge recombination against redox shuttles. Under the optimized conditions, DSSCs using thiophene-fused porphyrins T-Ph and T- t BuPh achieved a remarkable power conversion efficiency (PCE) of 11.5%. This is high compared to those with reference porphyrins, GY50 possessing steric hindrance due to the orthogonal orientation of a V-shaped diarylamino group to the porphyrin plane and DfZnP without the bulky umbrella-shaped m-terphenyl, demonstrating the proof of our concept. More importantly, the cosensitized DSSC using T- t BuPh and the complementary dye XY1B afforded the highest PCE of 12.3% ever reported for DSSCs with fused porphyrin dyes. This demonstrates that the "umbrella-shaped m-terphenyl" design is an attractive methodology for enhancing the photovoltaic performance of DSSCs with highly pi-extended planar dyes, especially fused porphyrin dyes.