Thin-film transistor and preparation method thereof, array substrate and display device

The invention discloses a thin-film transistor and a preparation method thereof, an array substrate and a display device and relates to the technical field of display. The invention aims at solving the problems of worse sealing connection between an electrode thin film and adjacent thin-film layers in the thin-film transistor of the prior art and the like. The thin-film transistor comprises a grid electrode, a source electrode, a drain electrode and a buffering layer, wherein the buffering layer is positioned at one side or the two sides of the grid electrode, the source electrode or the drain electrode; and the buffering layer is made of copper alloy materials which contain nitrogen element or oxygen element and also contain aluminium element. The thin-film transistor is used for the display device.