A photo detector device for a display device includes many first conductive lines, many second conductive lines orthogonal to the first conductive lines, many switching transistors, and many photosensitive transistors. Each of the switching transistors includes a drain, a source, and a gate, wherein the sources are electrically connected to the second conductive line, the gates are electrically connected to the first conductive line, and the first conductive lines receive a control signal to control on/off states of the switching transistors. Each of the photosensitive transistors includes a drain, a source, and a gate, wherein the photosensitive transistor sources are electrically connected to the drains of the switching transistors, and the photosensitive transistor gates are connected to and maintained at the potential of the photosensitive transistor drains.