Provided are a dual-junction thin film solar cell assembly, and manufacturing method thereof. The solar cell assembly is formed by multiple cell units connected in series, and each cell unit comprises a bottom cell and a top cell. The bottom cell is provided with a rear-side metal electrode layer (300), and the top cell is provided with a patterned front-side metal electrode layer (200). The bottom cell is a polycrystalline Ge bottom cell layer (106), and the top cell is a GaAs cell. An N-type diffusion layer (108), an N-type buffer layer, an N-type region (112) of a tunnel junction, and a P-type region (114) of the tunnel junction are sequentially grown from the polycrystalline Ge bottom cell layer to the top cell. An antireflection layer (400) is formed on the front-side metal electrode layer. In the dual-junction cell employing a GaAs substrate (100), and employing the polycrystalline germanium and the GaAs respectively as the bottom cell and the top cell, a bandgap of the polycrystalline germanium bottom
