NOVELTY - The device (200) has a transparent common substrate (204) comprising a light-receiving surface (205) parallel to longitudinal direction. A heavily doped P-layer (216) of a thin-film photovoltaic cell (202b1) is arranged coplanar to a heavily doped N-layer (214) of another thin-film photovoltaic cell (202b2). The heavily doped layers of the former photovoltaic cell are extended under the heavily doped layer of the latter photovoltaic cell. The overlapped layers form an area of a tunnel junction (210) through which the photovoltaic cells are electrically connected to each other in series.    USE - Monolithic thin-film photovoltaic device i.e. monolithic thin-film solar cell (MTF-SC).    ADVANTAGE - The device has a transparent common substrate comprising a glass plate or flexible plastic material, a pre-coated anti-reflection index-matching film and a planar surface on which electrodes of photovoltaic cell of individual tandem solar cell (TCS) and interconnection between the adjacent TSC are formed, so that light reflection is reduced, light-trapping efficiency of the substrate is improved and the design eliminates light-shadowing features such as metal contacts and lines, on a front surface of the monolithic thin-film solar cell (MTF-SC), thus allowing to use maximum amount of incoming radiation in an efficient manner.    DETAILED DESCRIPTION - The P-layer, I-layer and N-layer are made of materials selected from a group consisting of hydrogenated amorphous silicon, microcrystalline, nanocrystalline hydrogenated silicon, copper-indium-selenium and copper- indium-gallium-selenium.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross-sectional view of a monolithic thin-film photovoltaic device comprising a set of individual TSC connected in series.    Monolithic thin-film photovoltaic device (200)    TSCs (202a-202n)    Thin-film photovoltaic cell (202b1, 202b2)    Transparent common substrate (204)    Light-receiving surface (205)    Tunnel junction (210)    Heavily doped N-layer (214)    Heavily doped P-layer (216)