There is provided a thin film transistor including: a substrate; a gate electrode and a first electrode in a single layer on the substrate; an active layer above the first electrode, an orthographic projection of the active layer on the substrate at least partially covers an orthographic projection of the first electrode on the substrate; a first insulation layer covering the gate electrode, the first electrode, the active layer, a portion of the substrate exposed between the gate electrode and the active layer, and another portion of the substrate exposed between the gate electrode and the first electrode; and a second electrode above the first insulation layer, an orthographic projection of the second electrode on the substrate at least partially covers the orthographic projection of the active layer on the substrate, and the second electrode is connected to the active layer through a via-hole in the first insulation layer.