Provided are a dual-junction thin film solar cell assembly, and manufacturing method thereof. The cell assembly is formed by multiple cell units connected in series, and each cell unit comprises a selectively grown substrate (105), a bottom cell (106), and a top cell (126). The top cell (126) is provided with a front-side metal electrode layer (200), and the selectively grown substrate (105) comprises a metal base (100), a patterned insulation layer (102), and an N-type microcrystalline germanium seed layer (104), the insulation layer (102) is formed on the metal base (100), and the N-type microcrystalline germanium seed layer (104) is in the pattern formed by the insulation layer (102). The bottom cell (106) is a polycrystalline germanium bottom cell layer, and the top cell (126) is an GaAs cell. An N-type diffusion layer (108), an N-type buffer layer (110), 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 germanium
