NiCo2O4 arrays with a tailored morphology as hole transport layers of perovskite solar cells.

Inorganic p-type semiconductors have broadly served as hole transport materials (HTLs) in perovskite solar cells (PSCs) in recent years. Among them, NiCo2O4 with its excellent conductivity and hole mobility is the emerging candidate for HTLs and is attracting increasing attention. Here, we employ a simple hydrothermal method to fabricate high-quality mesoporous NiCo2O4 films as HTLs of PSCs. The study finds that the morphology of NiCo2O4 can be regulated from nanosheets (NSs) to nanowires (NWs) as the hydrothermal reaction time increases, and the morphology of NiCo2O4 significantly affects the device performance. Specially, the device with NWs achieves a best efficiency of 11.58%, ascribed to the fact that such a one dimension material could provide a straight path for hole extraction/transport. And benefiting from the mesoporous structures of NiCo2O4 films, all the devices exhibited a very repeatable and desirable long-term stability. Overall, this work develops alternative NiCo2O4 nanostructure-based HTLs and opens up new opportunities in fabricating PSCs.