NiN-Passivated NiO Hole-Transport Layer Improves Halide Perovskite-Based Solar Cell

The interfaces between inorganic selective contacts and halide perovskites (HaPs) are possibly the greatest challenge for making stable and reproducible solar cells with these materials. NiO, an attractive hole-transport layer as it fits the electronic structure of HaPs, is highly stable and can be produced at a low cost. Furthermore, NiO can be fabricated via scalable and controlled physical deposition methods such as RF sputtering to facilitate the quest for scalable, solvent-free, vacuum-deposited HaP-based solar cells (PSCs). However, the interface between NiO and HaPs is still not well-controlled, which leads at times to a lack of stability and V_oc losses. Here, we use RF sputtering to fabricate NiO and then cover it with a NiN layer without breaking vacuum. The NiN layer protects NiO doubly during PSC production. Firstly, the NiN layer protects NiO from Ni³⁺ species being reduced to Ni²⁺ by Ar plasma, thus maintaining NiO conductivity. Secondly, it passivates the interface between NiO and the HaPs, retaining PSC stability over time. This double effect improves PSC efficiency from an average of 16.5% with a 17.4% record cell to a 19% average with a 19.8% record cell and increases the device stability.