Self-powered near-infrared (NIR) detection technologies attract immense interest both from scientific and industrial perspectives due to their vital applications in environmental monitoring, night vision, and imaging in remote locations. Solution-processed colloidal semiconductor nanocrystals (NCs) have been a centre of interest among third-generation devices, offering band gap tunability, strong quantum confinement, and lower cost and large-scale fabrication. Unfortunately, the dominant NC families employed in infrared (IR) detectors are based on toxic heavy metals, such as Cd, Pb, and Hg, which restrict their use in consumer electronics and biomedical technologies under the European RoHS regulation (Restriction of the Use of Hazardous Substances). To address this limitation, silver chalcogenide (Ag₂E, where E = S, Se, or Te)-based NCs have emerged as a promising class for near IR and short-wave IR detection, offering favourable bandgaps in the IR region (Ag₂S ~0.9-1.3 eV, Ag₂Se ~0.15 eV, Ag₂Te ~0.3 eV), making them appealing from health and environmental safety perspectives. However, most Ag2E NC-based photodetectors still rely on solid-state ligand exchange protocols because solution-phase ligand exchange often fails due to poor colloidal stability and surface degradation of NCs during the process. A major disadvantage of this method is that it requires multiple layer-by-layer processing steps, which increase fabrication time, material consumption, and can lead to non-uniform or low-quality films. Most attempts at Ag₂E NC solution-phase ligand exchange fail because the weak Ag–chalcogen surface bonds, which can easily be disrupted by polar solvents or reactive short ligands, lead to aggregation and/or loss of optical and electronic properties.

In this study, we report a versatile Ag₂S NC ink based on a solution-phase ligand exchange strategy that yields fully passivated, highly dispersible and stabile NCs compatible with direct deposition of functional device layers. We investigated the impact of this ligand engineering on the performance of Ag₂S NCs-based photodetectors fabricated on flexible textile substrates with asymmetric electrode by following our previous protocol.^1,2 Importantly, we prepared highly conductive films on flexible textile substrates by directly depositing Ag₂S NC ink without further chemical treatment. The devices fabricated demonstrate strong self-powered responsivity across the 400–1200 nm band with excellent mechanical flexibility (devices demonstrated excellent mechanical flexibility, maintaining high performance even after 500 bending cycles), enabling applications in continuous health monitoring, smart clothing, and night-vision technologies under the European RoHS regulations.