The present disclosure provides an image sensor device and a method of forming the image sensor device. In an example, an image sensor device includes a substrate having a front surface and a back surface; a sensor element disposed at the front surface of the substrate, the sensor element being operable to sense radiation projected toward the back surface of the substrate; and a transparent conductive layer disposed over the back surface of the substrate, the transparent conductive layer at least partially overlying the sensor element. The transparent conductive layer is configured for being electrically coupled to a bottom portion of the sensor element.