Disclosed are an array substrate, a preparation method thereof, a display panel and a display device. The array substrate includes a base substrate, a first thin film transistor, a photosensitive sensor, and a dielectric layer. The first thin film is on the base substrate and includes a gate, a drain, a source and a conductive channel between the drain and the source. The photosensitive sensor has the drain of the first thin film transistor as an electrode of the photosensitive sensor. The dielectric layer covers the conductive channel of the first thin film transistor, where the dielectric layer is a metal oxide film.