Suppressing Redox Reactions at the Perovskite-Nickel Oxide Interface with Zinc Nitride to Improve the Performance of Perovskite Solar Cells

For p-i-n perovskite solar cells (PSCs), nickel oxide (NiO_x) hole transport layers (HTLs) are the preferred interfacial layer due to their low cost, high mobility, high transmittance, and stability. However, the redox reaction between the Ni^≥3+ and hydroxyl groups in the NiO_x and perovskite layer leads to oxidized CH₃NH₃⁺ and reacts with PbI in the perovskite, resulting in a large number of non-radiative recombination sites. Among various transition metals, an ultra-thin zinc nitride (Zn₃N₂) layer on the NiO_x surface is chosen to prevent these redox reactions and interfacial issues using a simple solution process at low temperatures. The redox reaction and non-radiative recombination at the interface of the perovskite and NiO_x reduce chemically by using interface modifier Zn₃N₂ to reduce hydroxyl group and defects on the surface of NiO_x. A thin layer of Zn₃N₂ at the NiO_x/perovskite interface results in a high Ni³⁺/Ni²⁺ ratio and a significant work function (WF), which inhibits the redox reaction and provides a highly aligned energy level with perovskite crystal and rigorous trap-passivation ability. Consequently, Zn₃N₂-modified NiO_x-based PSCs achieve a champion PCE of 21.61%, over the NiO_x-based PSCs. After Zn₃N₂ modification, the PSC can improve stability under several conditions.