KCS

Despite recent advances in lead-free colloidal nanocrystals (NCs) silver bismuth sulfide (AgBiS2) have demonstrated promising aspects as Eco-friendly photoactive layer in photovoltaics (PVs). The conventional halide-treated NCs provide insufficient defect passivation and poor morphology, still limiting its renaissance. Herein, we revisit the surface chemistry of the AgBiS2 NCs treated with a variety of organic ligands and reveal that reactive amines and thiols significantly deform the surface by exfoliating metal ions, making the surface prone to ambient oxidation. In contrast, electron-withdrawing carboxylic acid of 3-mercaptopropionic acid (MPA) alleviate the reactivity of thiol, providing better surface passivation without detrimental effects. Nevertheless, insufficient electronic coupling over the NCs originating from spatial separation still inhibits electric conductivity, responsible for poor performance of the NCPVs. To deploy the advantages without adverse effects, a bi-layered NC photoactive layer with a combination of existing halide-passivated NC and an organic-passivated NC provides synergistic effect in the PV performance, attributed to a construction of cascade energetic landscape that extending depletion region and improved defect passivation. Consequently, by using 3-mercaptopropionic acid (MPA), a power conversion efficiency of 6.39% in AgBiS2 NC-based PV is demonstrated, responsible for the concurrent suppression of charge recombination and enhancement in charge extraction.