Overcome Low Intrinsic Conductivity of NiO_x Through Triazinyl Modification for Highly Efficient and Stable Inverted Perovskite Solar Cells

Nickel oxide (NiO_x) is a promising hole transport material in inverted organic-inorganic metal halide perovskite solar cells. However, its low intrinsic conductivity hinders its further improvement in device performance. Here, we employ a trimercapto-s-triazine trisodium salt (TTTS) as a chelating agent of Ni²⁺ in the NiO_x layer to improve its conductivity. Due to the electron-deficient triazine ring, the TTTS complexes with Ni²⁺ in NiO_x via a strong Ni²⁺-N coordination bond and increases the ratio of Ni³⁺:Ni²⁺. The increased Ni³⁺ concentration adjusts the band structure of NiO_x, thus enhancing hole density and mobility, eventually improving the intrinsic conductivity of NiO_x. As a result, the device with TTTS modification displays a champion power conversion efficiency (PCE) of 22.81%. The encapsulated device based on a modified-NiO_x layer maintains 94% of its initial power output at the maximum power point and continuous one-sun illumination for 1000 h at 45 °C. In addition, the unencapsulated target devices also maintain 92% at 60 ± 5% relative humidity and 25 °C in the air for 5000 h; and 91% at 85 °C in a nitrogen atmosphere for 1000 h. The research provides an effective strategy to enhance PCE and stability of inverted PSCs via modifying NiO_x films with triazine molecule.