Tetrapropyl-substituted palladium phthalocyanine used as an efficient hole transport material in perovskite solar cells

This report presents two tetrapropyl-substituted metal phthalocyanines (PdPrPc and ZnPrPc) used as dopant-free hole transport materials (HTMs) for perovskite solar cells (PSCs). The substitution of Pd atom did not significantly reduce the mobility of the material but increased its lowest unoccupied molecular orbital (LUMO) level. Owing to spin-orbit coupling, the PdPrPc is thought to have a longer carrier diffusion length than that of the ZnPrPc. The higher LUMO level together with the longer carrier diffusion length of the PdPrPc reduced the hole-electron recombination, which led to a higher FF value of its PSC, giving rise to a higher PCE of 18.09% than that of the ZnPrPc-based device. Further, the PdPrPc-based PSC exhibited an increased stability compared with the ZnPrPc-based one. The result indicates the potential application of MPcs containing heavier atoms in efficient and stable PSCs.