CuInSe2 is a semiconductor used in solar cells that has appreciable Cu ion conductivity. These authors have used 0.25 Angstrom synchrotron X-radiation to analyze its structure. It is shown that the application of a strong electric field leads to a decrease in electron density on the Cu sites, which sheds light on the role of Cu electromigration in transistor formation (see Figure) and in the photovoltaic activity of CuInSe2.