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 NiOx film as a hole-transporting layer. Since the surface of the NiOx 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 NiOx film reached approximately 15°. After the treatment, the valence band level of the NiOx film was deeper by about 0.15 eV. The maximum efficiency of the NiOx-based device under the optimized O2 plasma condition reached 12.3%.