Ligand engineering of solution-processed NiOx for high-performance n–i–p perovskite photovoltaics

Abstract

In n–i–p halide perovskite solar cells (PSCs), replacing organic p-type semiconductors with inorganic alternatives holds significant potential for enhancing long-term stability. While nickel oxide (NiO_x) has gained prominence as a hole transport layer (HTL) in inverted architectures, traditional solution-deposition techniques for regular configurations face inherent limitations in reconciling colloidal stability, interfacial integrity, and charge transport efficiency. This study introduces a bifunctional ligand design strategy that combines short- and long-chain molecules to engineer solution-processable NiO_x nanoparticles into high-performance HTLs. The coordinated ligand system achieves three synergistic functions: (1) colloidal stabilization via synergistic adsorption energy modulation, (2) enhanced interparticle charge transfer through controlled C/Ni ratio reduction, and (3) interfacial energy alignment enabled by ligand-mediated charge redistribution. Additionally, incorporating 4.2 wt% dopant-free poly(3-hexylthiophene) (P3HT) into the optimized NiO_x matrix (termed NiPT-HTL) yields record power conversion efficiencies of 24.32% (0.09 cm²) for small-area devices and 22.34% (21.8 cm²) for minimodules, setting a new benchmark for NiO_x-based n–i–p architectures. Moreover, the minimodules exhibit exceptional stability with <5% degradation after 700 hours of damp-heat operation (60 °C/50% RH). This work resolves the inherent incompatibility between solution processability and optoelectronic performance in metal oxide HTLs, establishing a materials innovation framework that bridges fundamental research with the scalable manufacturing of stable perovskite photovoltaics.