The present invention discloses a solar cell having a multi-layered structure that is used to generate, transport, and collect electric charges. The multi-layered nanostructure comprises a cathode, a conducting metal layer, a photo-active layer, a hole-transport layer, and an anode. The photo-active layer comprises a tree-like nanostructure array and a conjugate polymer filler. The tree-like nanostructure array is used as an electron acceptor while the conjugate polymer filler is as an electron donor. The tree-like nanostructure array comprises a trunk part and a branch part. The trunk part is formed in-situ on the surface of the conducting metal layer and is used to provide a long straight transport pathway to transport electrons. The large contact area between the branch part and the conjugate polymer filler provides electron-hole separation.