Journal Article

Nickel oxide (NiO_x) serves as a promising inorganic hole transport layer (HTL) for efficient and stable Sn-Pb mixed perovskite solar cells (PSCs). However, intrinsic drawbacks of NiO_x limit the efficiency of PSCs. In this study, we introduce 2D Ti₃C₂T_x MXenes, known for their high mobility and diverse functional groups, into NiOx HTLs to address these limitations. The addition of MXenes significantly enhances the conductivity of the NiO_x layer without increasing the concentration of Ni³⁺. The abundant ─OH and ─O functional groups on MXenes form strong coordination bonds with Ni^3⁺ defects, effectively mitigating adverse reactions with organic cations and preventing oxidation of Sn²⁺ at the buried perovskite interfaces. Furthermore, these functional groups create additional nucleation sites that modulate perovskite crystallization kinetics, resulting in larger grain sizes and more compact buried interfaces. The dipoles formed by the MXenes improve energy level alignment at the NiO_x/perovskite interfaces, enhancing hole extraction efficiency. Consequently, FASn_0.5Pb_0.5I₃ PSCs utilizing MXene-NiO_x HTLs achieved a remarkable power conversion efficiency (PCE) of 22.50% (20.04% certified), among the highest efficiencies reported for FA-based Sn-Pb PSCs with NiO_x HTLs. Additionally, unencapsulated devices show improved stability, retaining approximately 80% of their initial PCE after 600 h of continuous operation at maximum power point.