Coupling Design in the Direct Synthesis of AgBiS₂ Nanocrystal Inks for Efficient and Eco-friendly Photovoltaics

Direct synthesis of conductive AgBiS₂ nanocrystal (NC) ink provides a promising platform for eco-friendly, low-cost optoelectronic applications. However, current synthesis relies on single thiol ligands to maintain colloidal stability, which severely impairs inter-NC charge conductivity and ultimately limits device photovoltaic performance. Here, we utilize butylamine (BA) to solubilize cationic precursors, followed by 3-chloro-1-propanethiol (CPT) to engineer the NC surface and interparticle packing. This method produces NCs with reinforced inter-NC coupling, while the surface-anchored CPT ligands can release Cl^- ions upon thermal annealing to achieve superior surface passivation. As a result, the power conversion efficiency (PCE) of AgBiS₂ NC solar cells is improved from 8.91% to 9.82%, and unencapsulated devices retain more than 90% of the initial PCE after 3 months under ambient conditions. This work advances the potential of directly synthesized NC inks for high-performance and low-cost optoelectronic applications.