An image sensor with an array of image sensor pixels is provided. Each pixel may include a photodiode, a storage diode, and associated circuitry formed in a semiconductor substrate. Buried light shields may be formed on the substrate to prevent regions between two adjacent photodiodes from being exposed to incoming light. In one embodiment, a shallow trench isolation (STI) structure may be formed between the photodiode and the storage diode, and a conductive layer formed from optically absorptive material may be constructed at the bottom of the STI structure. A via may be formed through the STI structure to help bias the conductive layer using a ground or negative voltage. In another embodiment, an isolation ring structure may be formed at the base of the buried light shields. The isolation ring structure may be formed from optically absorptive material and can optionally be biased using a ground or negative voltage.