Dye-Sensitized Ternary Copper Chalcogenide Nanocrystals: Optoelectronic Properties, Air Stability, and Photosensitivity

We report on the effect of ligand exchange of Cu2SeyS1-y and Cu2Se nanocrystals (NCs) with the organic pi system cobalt beta-tetraaminophthalocyanine (CoTAPc) and analyze the changes in the structural, optical, and electric properties of thin films of these hybrid materials. A strong ligand interaction with the surface of the NCs is revealed by UV/vis absorption and Raman spectroscopy. Grazing incidence small-angle X-ray scattering studies show a significant contraction in the interparticle distance upon ligand exchange. For copper-deficient Cu2-xSe, this contraction has a negligible effect on electric transport, whereas for copper-deficient Cu2-xSeyS1-y, the conductivity increases by 8 orders of magnitude and results in metal-like temperature-dependent transport. We discuss these differences in the light of varying contributions of electronic vs ionic transport in the two materials and highlight their effect on the stability of the transport properties under ambient conditions. With photocurrent measurements, we demonstrate high optical responsivities of 200-400 A W-1 for CoTAPc-capped Cu2SeyS1-y and emphasize the beneficial role of the organic pi-system in this respect, which acts as an electronic linker and an optical sensitizer at the same time.