Evolution of the formation of AgBiS2 colloidal nanocrystals for optoelectronic devices

Abstract

AgBiS₂ has emerged as a promising environmentally friendly nanocrystal (NC) for optoelectronic applications due to its broad absorption spectrum in the visible and near-infrared regions. However, a performance ceiling has hindered the development of AgBiS₂-based solar cells, with power conversion efficiencies (PCE) remaining stagnant at 9–10%. This limitation arises from a lack of understanding of its fundamental properties, such as its crystal structure and electronic properties, which are crucial for further optimisation. Here, we focus on a comprehensive investigation of the synthesis and formation of AgBiS₂ NCs. Utilising Rietveld refinement, the crystallographic structure and phase purity are meticulously analysed, ensuring precise insights into the material's formation pathways. Furthermore, the constructed phase diagram of the Ag–Bi–S system reveals the threshold temperature at 160 °C to obtain pristine AgBiS₂ NCs, while below that, Ag₂S NCs are dominant. Density of states (DOS) analysis shows a similar bandgap with an experimental result of 0.8 eV, confirming the semiconductor properties. High-performance photodetectors of AgBiS₂ NCs are demonstrated, exhibiting high responsivity, although only using a few monolayers of the nanocrystal assemblies. These results bridge the knowledge gap in AgBiS₂ formation mechanisms and electronic behaviour, establishing a robust foundation to enhance its optoelectronic performance and integrate it into advanced device architectures.