Suppressing NiO_x/CsPbIBr₂ Interfacial Redox Reactions and Band Energy Misalignment in Perovskite Solar Cells

Inverted inorganic CsPbIBr₂ perovskite solar cells (PSCs) employing NiO_x as the hole-transport layer are promising long-term stable and semi-transparent photovoltaic devices. Nevertheless, their performance is often constrained by unfavorable interfacial phenomena, including detrimental redox reactions between Ni³⁺ in NiO_x and I^- in perovskite, as well as band energy misalignment at the NiO_x/CsPbIBr₂ interface. In this work, we introduce an N-dodecylphosphonic acid (NDPA) interfacial modification strategy, where the phosphonic groups of NDPA anchor onto the NiO_x surface. This tailored interface not only suppresses interfacial redox reactions but also alleviates energy level mismatch and releases the residual tensile stress, thereby facilitating charge transport and reducing non-radiative recombination losses. As a result, the optimized PSCs deliver a champion power conversion efficiency of 9.28% with a high open-circuit voltage (V_oc) of 1.12 V, positioning it among the best-performing inverted CsPbIBr₂ PSCs reported to date. The modified devices retain 79% of their initial efficiency after 1300 h of storage in a nitrogen-filled glovebox, underscoring their potential for practical photovoltaic applications.