Novel π-extended porphyrin-based hole-transporting materials with triarylamine donor units for high performance perovskite solar cells

Efficient hole transporting materials (HTMs) for perovskite solar cells (PrSCs) is highly desired in emerging solar cell technologies. Three HTMs comprising a coplanar porphyrin core with different substituted electron donating triarylamine (TAA) groups (coded as SGT-061, SGT-062, and SGT-063) were successfully developed and used as HTMs for PrSCs. The porphyrin-based HTMs with more bulky donor groups (SGT-062 and SGT-063) possess the larger dihedral angle between alkoxy-substituted phenyl ring and the donor TAA core, leading to the greater interference for the dense molecular arrangement and reducing the pi-pi stacking of HTM molecules. But SGT-061 with a less bulky donor enables a tight molecular arrangement to increase the pi-pi stacking between molecules. This renders SGT-061 to have a higher hole mobility than that of SGT-062 and SGT-063 HTMs with bigger donor groups. Moreover, the dynamic charge transfer process of perovskite/various HTM films was studied by time-resolved photoluminescence decay. And SGT-061 exhibited more efficient hole extraction ability than that of SGT-062 and SGT-063. This could be ascribed to better hole mobility and better co-facial pi-pi stacking between molecules. These results indicate that a less bulky electron donor unit is a preferred peripheral group for developing porphyrin based HTMs for efficient perovskite solar cells.