Synergistic Opto-Electrical Modification of the Buried Interface for Inverted Wide-Bandgap Perovskite Solar Cells

Nickel oxide (NiO_x) is a promising hole transport layer (HTL) in inverted wide-bandgap perovskite solar cells (WB-PSCs), but its relatively low conductivity necessitates further improvement. In this work, aluminum oxide nanoparticles (Al₂O₃ NPs) were doped into the NiO_x HTL. First, the partial Al³⁺ ions form Al–O–Ni bonds with Ni³⁺ and O^2–, preventing PEAI from reducing Ni³⁺ and thereby affecting the conductivity of the NiO_x film. Second, the Al₂O₃ NPs enhance the optical properties of the NiO_x film by introducing Mie scattering, which increases light utilization in the perovskite layer and boosts the WB-PSCs’ short-circuit current density (J_SC). Additionally, phenethylammonium iodide (PEAI) is applied to passivate the buried interface of the perovskite film, reducing defects. As a result, a champion power conversion efficiency (PCE) of 21.29% is achieved for a 1.65 eV bandgap WB-PSC. This work provides a synergistic strategy for improving both the electrical and optical properties of NiO_x-based HTLs.