Electrodeposition of crystalline germanium thin films by the electrochemical liquid-liquid-solid method

•In the aqueous solution system, germanium films were deposited with liquid metal at room temperature and pressure.•Ga-doped p-type germanium films were deposited on Cu heterogeneously to form the Ge/Cu heterojunction.•The Ge/Cu heterojunction device prepared by ec-LLSS method has a certain basis for the preparation of solar cells.