DC Reactive‐Sputtered NiO _X Hole Transport Layers with Tailored Nickel Vacancies for Perovskite Single‐Junction and Textured Perovskite/Silicon Tandem Solar Cells

Abstract Sputtered nickel oxide (NiO _X ) is a promising material for hole transport layers (HTLs) in industrializing perovskite solar cells (PSCs) due to its scalable and conformal growth. However, its low conductivity and interfacial instability limit device performance. Herein, high‐quality undoped NiO _X (DC‐N) HTLs are developed fabricated via direct current (DC) reactive sputtering (Ni target) coupled with low‐temperature (≤ 200 °C) air annealing. By synergistically modulating process conditions, nickel vacancy density is tailoreded to balance photoelectric properties and interfacial stability of DC‐N HTLs, while elucidating trade‐offs among conductivity, transmittance, and interfacial stability. Contrastive analysis reveals that the DC‐N HTLs outperform conventional RF‐sputtered NiO _X HTLs (derived from ceramic targets, doped or undoped), mainly attributed to their outstanding conductivity, an ideal Ni ³⁺ /Ni ²⁺ ratio, good crystallization, and excellent interface properties, which mitigate parasitic absorption, recombination losses, and charge transport losses. By employing DC‐N HTLs, inverted PSCs with a 1.68 eV bandgap achieve a power conversion efficiency (PCE) of 20.71%, increasing to 22.45% with Me‐4PACz/Al ₂ O ₃ interlayers and thick‐film perovskite. Notably, integrating DC‐N HTLs into textured perovskite/silicon tandem solar cells delivered a PCE of 32.02% (1.0 cm ² aperture area), providing valuable insights for NiO _X ‐based tandem photovoltaics.