Various embodiments of the present disclosure are directed towards an image sensor. The image sensor includes a substrate having a first side and a second side. The substrate includes a pixel region. A photodetector is in the pixel region. A first doped region is in the pixel region. A second doped region is in the pixel region. The second doped region is vertically between the first doped region and the first side of the substrate. A doped well is in the substrate and laterally surrounds the pixel region. The doped well is partially in the second doped region. A portion of the second doped region is vertically between the doped well and the second side of the substrate. A trench isolation structure is in the semiconductor substrate and laterally surrounds the pixel region. A footprint of the trench isolation structure is within a footprint of the doped well.