High-Performance Near-Infrared Absorbing n-Type Porphyrin Acceptor for Organic Solar Cells

While the outstanding charge transport and sunlight harvesting properties of porphyrin molecules are highly attractive as active materials for organic photovoltaic (OPV) devices, the development of n-type porphyrin-based electron acceptors has been challenging. In this work, we developed a high-performance porphyrin-based electron acceptor for OPVs by substitution of four naphthalene diimide (NDI) units at the perimeter of a Zn-porphyrin (P-zn) core using ethyne linkage. Effective pi-conjugation between four NDI wings and the Pan core significantly broadened Q-band absorption to the near infrared region, thereby achieving the narrow band gap of 1.33 eV. Employing a windmill-structured tetra-NDI substituted P-zn-based acceptor (P-zn-TNDI) and mid-band gap polymer donor (PTB7-Th), the bulk heterojunction OPV devices achieved a power conversion efficiency (PCE) of 8.15% with an energy loss of 0.61 eV. The PCE of our P-zn-TNDI-based device was the highest among the reported OPVs using porphyrin-based acceptors. Notably, the amorphous characteristic of P-zn-TNDI enabled optimization of the device performance without using any additive, which should make industrial fabrication simpler and cheaper.