Earth-Abundant Chalcopyrite (CuFeS₂) Nanocrystals: Structural, Optical and Hole Transport Properties

Chalcopyrite nanocrystals (NCs), especially CuFeS₂, have attracted considerable attention of the researchers due to their earth-abundance, low toxicity, and solution-processing for the fabrication of the thin film devices. However, control over the phase purity and stability during the synthesis of ternary and quaternary NCs remains challenging. Here, we report the thermal-injection colloidal synthesis of CuFeS₂ NCs using iron (II) bromide (FeBr₂), copper (II) acetaylacetonate (Cu(acac)₂), and elemental sulfur (S) as Fe, Cu and S sources respectively. Controlled reaction temperature and growth time yields stable and phase-pure ternary CuFeS₂ NCs, exhibiting tetragonal crystal structure in the chalcopyrite phase. With increasing growth time, the optical absorption peak slightly red shifts, and eventually disappears at longer growth times. The relationship between the optical properties and the two intermediate bands located within the fundamental band gap is also discussed. The electronic properties CuFeS₂ NCs based films show that this material is a promising hole transport material for energy harvesting applications.