Ordered vacancy compounds and nanotube formation in CulnSe2-CdS core-shell nanowires

CulnSe(2) related materials-based heterojunction diodes have received much attention, owing to their highest power conversion efficiency (19.5%) among all the thin-film solar cell technologies. Important issues on the microstructure and formation mechanism of CulnSe(2)-CdS p-n heterojunction persist due to the complexity of polycrystalline films and invasive sample preparation for characterization. Here, we investigated the microstructure, chemical composition, and formation mechanism of the junction with CulnSe(2)-CdS core-shell nanowires, where nanowire geometry affords single-crystalline nanograins for direct characterization. A coherent CdS shell can be epitaxially deposited onto the CulnSe(2) nanowire with chemical bath deposition even at 60 degrees C. For the first time, ordered vacancy compound nanodomains induced by fast outward diffusion of Cu ions were directly observed near the interface of epitaxial CIS-CdS heterostructure. The core-shell nanowires can be transformed into nanotubes with chemical bath deposition progression through a nanoscale Kirkendall effect. Our results provide important understanding of CulnSe(2)-CdS heterojunctions for developing better CulnSe(2) solar cells.