Cuprous oxide is a narrow bandgap (1.8–2.2 eV) p-type semiconductor that is abundant and cheap. Because of this, it can also absorb a substantial portion of the solar spectrum. Its conduction band and valence band positions are theoretically appropriate to facilitate both the CO2 reduction and water splitting reactions, however, its main disadvantage is that it suffers from photocorrosion.

Properties

The solid is diamagnetic. In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are tetrahedral. The structure thus resembles in some sense the main polymorphs of SiO2, and both structures feature interpenetrated lattices.

Copper(I) oxide dissolves in concentrated ammonia solution to form the colourless complex [Cu(NH3)2]+, which is easily oxidized in air to the blue [Cu(NH3)4(H2O)2]2+. It dissolves in hydrochloric acid to give solutions of CuCl?

Dilute sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively.

Cu2O degrades to copper(II) oxide in moist air.

Uses

Cuprous oxide (Cu2O) can be used as a potential candidate in solar-energy conversion, gas sensors, magnetic storage, and electronics. 

Cuprous oxide is commonly used as a pigment, a fungicide, and an antifouling agent for marine paints. Rectifier diodes based on this material have been used industrially as early as 1924, long before silicon became the standard. Copper(I) oxide is also responsible for the pink color in a positive Benedict's test.

In December 2021, Toshiba announced the creation of a transparent cuprous oxide (Cu2O) thin-film solar cell. The cell achieved an 8.4% energy conversion efficiency, the highest efficiency ever reported for any cell of this type as of 2021. The cells could be used for high-altitude platform station applications and electric vehicles.