The present application discloses A thin film transistor (TFT), including: a substrate; a source-drain layer comprising a source electrode and a drain electrode over the substrate; and an active layer comprising a poly-Si pattern and an amorphous-Si pattern having contact with the poly-Si pattern over the substrate. The amorphous-Si pattern is between the poly-Si pattern and the source-drain layer; the source electrode overlaps with the poly-Si pattern and the amorphous-Si pattern respectively in a direction substantially perpendicular to a surface of the substrate; and the drain electrode overlaps with the poly-Si pattern and the amorphous-Si pattern respectively in the direction substantially perpendicular to the surface of the substrate.