Influence of O2 plasma treatment on NiO x layer in perovskite solar cells.

We fabricated perovskite solar cells (PSCs) with an inverted p–i–n planar structure using a NiO_x film as a hole-transporting layer. Since the surface of the NiO_x film fabricated by sputtering is hydrophobic, O₂ plasma treatment under various conditions was performed to improve its wettability. Water contact angles after the treatment under both normal and weak conditions on the NiO_x film reached approximately 15°. After the treatment, the valence band level of the NiO_x film was deeper by about 0.15 eV. The maximum efficiency of the NiO_x-based device under the optimized O₂ plasma condition reached 12.3%. [ABSTRACT FROM AUTHOR]