Copper(I) selenide is an inorganic binary compound between copper and selenium, with the chemical formula Cu<sub>2</sub>Se.
Stoichiometric copper selenide is a zero-bandgap material with metal-like behavior. Copper-deficient Cu<sub>2âÂÂx</sub>Se (non-stoichiometric) is an intrinsic p-type semiconductor with direct and indirect bandgap energies in the range of 2.1âÂÂ2.3 eV and 1.2âÂÂ1.4 eV respectively. It is frequently grown as nanoparticles or other nanostructures.
Copper selenides are the most common selenium minerals. Cu<sub>2</sub>Se occurs as two polymorphs: berzelianite (isometric, more common) and bellidoite (tetragonal). Other copper selenide minerals include umangite, Cu<sub>3</sub>Se<sub>2</sub> and athabascaite, Cu<sub>5</sub>Se<sub>4</sub>.
Copper(I) selenide is produced in situ to form a protective black coating on iron or steel parts in some cold-bluing processes. Bluing solutions that operate in this manner will typically be labeled as containing selenous acid or selenium dioxide. It has also been investigated for use in the treatment of colon cancer.