Optoelectronic Effects of Chemical and Thermal Treatments on CuSbS₂Nanocrystal Thin Films

The use of nanocrystalline materials in optoelectronic devices has been studied extensively over the last decade. Their size-dependent properties, low cost, low energy solution processing, and the potential for flexible devices motivate this effort. However, many of these benefits are offset by challenges associated with the surface chemistry and multitude of grain boundaries that exist when nanocrystals are cast into thin films. Nanocrystal surface chemistry and material interfaces determine the key physical characteristics (e.g., conductivity, reactivity, charge) due to their large surface to volume ratio. Therefore, controlling the surface chemistry of nanocrystals is essential for optimizing the behavior of nanomaterials for optoelectronic applications. In this report, a comprehensive analysis on the effects of chemical and thermal treatments on CuSbS2 nanocrystal thin films, for their use as a solar energy absorber, is described. Chemical treatments were found to improve film densities, while mild thermal treatments increased the absorptivity coefficient and photocurrent response of the nanocrystal thin films. More specifically, CuSbS2 nanocrystal films that received CuCl2 and mild thermal treatments displayed the highest photocurrent density and highest charge carrier mobility. These results highlight how ligand exchange and thermal treatments help control CuSbS2 nanocrystal performance for thin-film solar technology.