The present disclosure provides an image sensor device that exhibits improved quantum efficiency. For example, a backside illuminated (BSI) image sensor device is provided that includes a substrate having a front surface and a back surface; a light sensing region disposed at the front surface of the substrate; and an antireflective layer disposed over the back surface of the substrate. The antireflective layer has an index of refraction greater than or equal to about 2.2 and an extinction coefficient less than or equal to about 0.05 when measured at a wavelength less than 700 nm.