Growth of CuInS2 Nanotubes from Cu2S-CuInS2 Heterostructures as a Potential Photovoltaic Material

Chemically synthesized nanostructures possess well-defined domains with an interconnected network, which helps the carriers to bypass the other material in the solar cell while moving to their respective electrodes. In this work, CuInS₂ films constituting CuInS₂ nanotubes and nanoparticles were fabricated using a hot-injection chemical technique, followed by sulfurization. Structural and microstructural investigations reveal Cu₂S nanoparticle formation at an early stage of growth of nanotubes, serving as possible catalyst sites for the subsequent anisotropic growth of the heterostructured hexagons. The crossover takes place over a number of intermediate stages. This sharing of the heterostructure by the hexagonal Cu₂S and chalcopyrite CuInS₂ minimizes the lattice distortion. The Cu₂S- CuInS₂ interface in the heterostructure acts as the nucleation center for CuInS₂ nanotubes. Optical absorption and Raman spectroscopy studies reveal better optical properties for CuInS₂ nanoparticles as compared to CuInS₂ nanotubes. Compared to all other nanostructures, nanowires or nanotubes tend to provide single-crystalline nanograins for direct characterization. These nanoparticles, especially the nanotubes, can be used to form an interconnected network structure of p- and n-type materials in bulk heterojunctions providing the key to improve solar cell efficiencies.