Various embodiments of the present disclosure are directed towards a pixel sensor. The pixel sensor includes a substrate having a front-side opposite a back-side. An image sensor element comprises an active layer disposed within the substrate, where the active layer comprises germanium. An anti-reflective coating (ARC) structure overlies the back-side of the substrate. The ARC structure includes a first dielectric layer overlying the back-side of the substrate, a second dielectric layer overlying the first dielectric layer, and a third dielectric layer overlying the second dielectric layer. A first index of refraction of the first dielectric layer is less than a second index of refraction of the second dielectric layer, and a third index of refraction of the third dielectric layer is less than the first index of refraction.