Sputtered Nickel Nitride on p-NiO_x Stabilizes Halide Perovskite, p-i-n Solar Cells

Stability is one of the significant barriers to commercialize halide perovskite, HaP, devices. Interfaces between inorganic selective contacts, preferred in terms of stability, and HaPs are one of the greatest challenges for making stable and reproducible devices. Nickel oxide (NiO_x) is an attractive hole-transport layer as it fits the electronic structure of HaPs, is highly durable, and can be produced at low cost. We demonstrate RF sputtering of NiO_x as a hole transport layer, followed by <i>in situ</i> deposition of an ultra-thin nickel nitride (Ni_yN) passivation layer. The Ni_yN coating protects Ni³⁺(in the oxide) from being reduced to Ni²⁺ during Ar plasma cleaning, thus maintaining NiO_x conductivity.<br/>Additionally, the Ni_yN forms a buffer layer that passivates the interface between NiO_x and the HaPs, protecting the HaP from the reactive Ni⁺³ species. This double effect improves the perovskite solar cell efficiency from an average of 16.5% (with 17.4% record) to 19% average (with 19.8% record) and increases the device stability, as shown by measurements over several days. We conclude that RF sputtering to deposit inorganic passivation layers is an innovative and viable step towards a scalable process of stable HaP-based solar cells.