In Situ Surface Metal Passivation on AgBiS2 Nanocrystals for Trap-Reduced Inverted Solar Cells

Silver bismuth sulfide (AgBiS₂) nanocrystal (NC) is a third-generation photovoltaic material used in solution-processed solar cells. During the NC purification process, the loss of surface ligand induces surface traps, leads to NC aggregation, and damages the device performance and operation stability. To address this issue, we employed an in situ metal passivation strategy for AgBiS₂ NCs to passivate the NC surface and protect the NCs from ligand dissociation. Our findings suggested that sodium is particularly effective in improving the solar cell performance by forming a protective shell on the surface, which passivates traps and inhibits trap recombination pathways. Quantitative NMR spectroscopy proves that the sodium-rich surface can bind with a higher density of oleate ligands after purification, resulting in a trap-reduced, robust thin film, which can further generate a higher photocurrent in the solar cells. The champion device achieved a short-circuit current density (J_SC) over 24 mA cm^–2 and light-soaking stability over 240 h, making it one of the best-performing p–i–n AgBiS₂ solar cells with superior photostability. Our metal-passivation study offers an alternative approach to synthesize trap-reduced AgBiS₂ NCs and fabricate high-performance solar cells.