A photoelectric conversion device, a manufacturing method thereof, and a display device are provided. The photoelectric conversion device includes a substrate and a thin film transistor unit layer arranged on the substrate. The photoelectric conversion device includes a photosensitive surface. The thin film transistor unit layer includes an active layer, a source-drain metal layer positioned at both ends of the active layer and electrically connected to the active layer, and a photonic crystal functional layer disposed on a side of the active layer away from the photosensitive surface.