Interfacial modification of NiO_x by self-assembled monolayer for efficient and stable inverted perovskite solar cells

NiO_x as a hole transport material for inverted perovskite solar cells has received great attention owing to its high transparency, low fabrication temperature, and superior stability. However, the mismatched energy levels and possible redox reactions at the NiO_x/perovskite interface severely limit the performance of NiO_x-based inverted perovskite solar cells. Herein, we introduce a p-type self-assembled monolayer between NiO_x and perovskite layers to modify the interface and block the undesirable redox reaction between perovskite and NiO_x. The self-assembled monolayer molecules all contain phosphoric acid function groups, which can be anchored onto the NiO_x surface and passivate the surface defect. Moreover, the introduction of self-assembled monolayers can regulate the energy level structure of NiO_x, reduce the interfacial band energy offset, and hence promote the hole transport from perovskite to NiO_x layer. Consequently, the device performance is significantly enhanced in terms of both power conversion efficiency and stability.