Synergistic carbon-based hole transporting layers for efficient and stable perovskite solar cells

Modification of hole transporting layers has proved an effective approach to improve the photoelectric conversion efficiency of perovskite solar cells. In this work, we report a highly dispersed graphene composite prepared by skillfully using the synergistic pi-pi interaction between graphene sheets and functional carbon nanotubes (f-CNTs). The graphene:f-CNTs HTLs demonstrate excellent conductivity and hole mobility. The hydrophobic graphene:f-CNTs HTL can also act as a scaffold for crystallization of perovskite layer and improve the device stability due to the beneficial interface. As a result, an improved PCE of 14.8% has been achieved with significant reproducibility. In addition, the optimized device with graphene:f-CNTs HTLs shows excellent stability and performance without encapsulation due to its neutral property. This approach can provide a good way for the future structure of perovskite solar cells.