H ₂ O ₂ -Modulated NiO _<i>x</i> Nanoparticle Film with High Conductivity and an Improved Heterojunction for Efficient Sb ₂ Se ₃ Solar Cells

Hole transporting layers (HTLs) play an important role in improving the performance of optoelectronic devices by efficiently transporting holes and blocking the reverse flow of electrons. In this study, we introduce hydrogen peroxide (H₂O₂)-modulated NiO_<i>x</i> (modulated-NiO_<i>x</i>) as an efficient HTL for antimony selenide (Sb₂Se₃) solar cells. H₂O₂ improves the dispersion of NiO_<i>x</i> nanoparticles in aqueous solution, increases the Ni³⁺/Ni²⁺ ratio, and leads to a more uniform and compact NiO_<i>x</i> film with superior electronic properties. The increased Ni³⁺/Ni²⁺ ratio results in a more matching energy level alignment between NiO_<i>x</i> and Sb₂Se₃ that is favorable for hole extraction. Density functional theory (DFT) calculations reveal that the modulated-NiO_<i>x</i>/Sb₂Se₃ interface exhibits a more ordered and planar interfacial structure with a well-aligned atomic position, promoting efficient charge transfer and suppressing interfacial recombination. As a result, Sb₂Se₃ solar cells employing modulated-NiO_<i>x</i> achieve a power conversion efficiency (PCE) of 9.06%, which ranks among the top efficiency for all-inorganic Sb₂Se₃ solar cells. Furthermore, the devices exhibit excellent stability, retaining 97% of the initial PCE after 30 days of storage in air. This study highlights the potential of H₂O₂-modified NiO_<i>x</i> as a high-performance HTL for efficient and stable Sb₂Se₃ solar cells, providing a promising pathway for advancing the Sb₂Se₃ photovoltaic technology.