NOVELTY - The device (10) has a substrate (20) that is transparent to solar radiation. A p-n junction active cell (40) that is formed over substrate absorbs a specific spectrum portion to convert solar radiation into electrical energy. A p-n junction active cell (60) that is formed over substrate absorbs other spectrum portion to convert solar radiation into electrical energy. The two spectrum portion of solar radiations is exclusive of each other and an optically reflective layer is formed over p-n junction active cell (60) and a carrier is formed over the optically reflective layer.    USE - Three-junction semiconductor solar cell device such as solar photovoltaic device e.g. III-nitride-material based monolithic multi-junction (MJ) solar cell for converting solar radiation into usable electrical energy, used in space application such as satellite, spacecraft or space station and terrestrial application.    ADVANTAGE - The production of highly economical and efficient and availability of high quality semiconductor materials can be facilitated and flexible choice of junction band-gaps covering a broad solar spectrum can be ensured. The appropriate device architecture design that maximizes current match and minimizes electrical/optical losses can be ensured. The environmental pollution related to material growth, device fabrication, material handling, and disposal can be avoided and manufacturing cost can be reduced. The full-solar-spectrum, high-efficiency, robust and low cost solar cells can be provided. As the energy band gap ranges from 0.7 eV to 6.0 eV, the absorption of solar energy from a much wider spectrum can be facilitated. The fabricating larger-area solar cell arrays can be enabled and changes in circuit design by simply altering the photomask pattern and device architecture can be permitted. The higher radiation damage threshold, a maximal effective solar absorption area, and higher broad-band solar transmission efficiency can be provided. The back-side illumination feature of an optically transparent substrate can be enhanced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for the method for making monolithic interconnected module.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of a three-junction solar cell device structure.    Three-junction solar cell device (10)    Sapphire substrate (20)    Buffer layer (30)    P-N junction active cell (40,60)    Interconnecting tunnel junctions (50,70)