NOVELTY - The flexible thin-film solar cell device comprises a substrate (15) comprising a mild steel (16) having a first surface and a second surface, a smooth protective nickel (Ni) coating (18) applied to the first surface of the mild steel and a protective alloy coating (26) formed over the protective Ni coating, a layer of a thin-film solar cell material deposited over the protective Ni coating, and junctions of a thin-film semiconductor material and a back-reflector layer stack. The protective Ni coating covers the second surface. The protective Ni or the alloy coatings is partially removed.    USE - The thin-film solar cell device is useful in a thin-film photovoltaic module (claimed).    ADVANTAGE - The flexible thin-film solar cell device has high stability, improved corrosion resistance and low contamination, and can be economically manufactured with high deposition rate, improved yield and efficiency and superior hardness, flatness and stiffness and without the need for vacuum equipment.    DETAILED DESCRIPTION - The flexible thin-film solar cell device comprises a substrate (15) comprising a mild steel (16) having a first surface and a second surface, a smooth protective nickel (Ni) coating (18) applied to the first surface of the mild steel and a protective alloy coating (26) formed over the protective Ni coating, a layer of a thin-film solar cell material deposited over the protective Ni coating, and junctions of a thin-film semiconductor material and a back-reflector layer stack. The protective Ni coating covers the second surface. The protective Ni or the alloy coatings is partially removed, and is a sacrificial layer. The back-reflector layer stack or one of the protective coatings is deposited by a wet chemical process. The solar cell device further comprises a back reflector stack (10) deposited over the protective Ni coating. The diffuse reflection of the portion of mild steel, the protective Ni coating, and the back reflector stack is 65-85% at 600-900 nm of the electromagnetic spectrum. The back-reflector stack comprises a highly reflective metallic layer (12), a conductive oxide of zinc, and optically transparent and electrically conductive textured layers. One of the textured layers is deposited by a wet chemical process. The junctions comprise amorphous silicon, microcrystalline or nanocrystalline silicon. The protective coatings are applied onto both sides of the substrate. The wet chemical process includes electroplating, electroless reductive plating, electroless displacement plating, chemical bath deposition, and/or sol-gel deposition using aqueous, organic metal salt solutions and ionic liquids as processing media. An INDEPENDENT CLAIM is included for a method of fabricating a thin-film solar cell device.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross sectional view of a silicon-based thin film solar cell device.    Back reflector stack (10)    Reflective metallic layer (12)    Substrate (15)    Mild steel (16)    Protective nickel coating (18)    Protective alloy coating. (26)