Biased Plasma Treated Nickel Oxide for High-Efficiency Perovskite/Silicon Tandem Solar Cells

Nickel oxide (NiO_x) hole transport layer deposited by magnetron sputtering shows high stability, low cost, high reproducibility, and scalability for perovskite and tandem solar cells. However, the performance of perovskite and tandem solar cells with sputtered NiO_x is limited by the defective interface and suboptimal energy band alignment. This work focuses on reconstructing the sputtered NiO_x surface with in situ biased plasma treatment (BPT). It is demonstrated that in situ BPT following sputtering induces both physical and chemical changes on the NiO_x surface, enabling a smoother and denser surface with controllable Ni³⁺/Ni²⁺ ratios. The in situ BPT NiO_x is proven to be effective in improving the conductivity of NiO_x, suppressing the non-radiation recombination, fine-tuning the energy band alignment, and facilitating the crystallinity of the perovskite. As a result, the power conversion efficiency (PCE) of wide bandgap perovskite solar cells is improved to 21.8% by the implementation of BPT NiO_x. Further integrating the BPT NiO_x into monolithic perovskite/silicon tandem solar cells results in a high PCE of 32.1% (certified 31.7%) with excellent operational stability.