DC Reactive-Sputtered NiO_X Hole Transport Layers with Tailored Nickel Vacancies for Perovskite Single-Junction and...

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 Ni³⁺/Ni²⁺ 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/Al₂O₃ 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 cm² aperture area), providing valuable insights for NiO_X-based tandem photovoltaics.