An optical sensor array substrate and an optical fingerprint reader are provided. The optical sensor array substrate includes a substrate including a detection area which includes a plurality of photosensitive pixels. Photosensitive pixel includes: a TFT arranged on the substrate; a storage capacitor arranged on the substrate and having a first capacitor plate, and a second capacitor plate electrically connected to the source or drain of the TFT; a photosensitive element located on one side of the storage capacitor away from the substrate, and having one end electrically connected to the second capacitor plate; a first electrode layer located on one side of the photosensitive element away from the substrate and electrically connected to another end of the photosensitive element. An orthographic projection of the second capacitor plate on the substrate at least partially overlaps with an orthographic projection of the first electrode layer on the substrate.