A self-photovoltaics-powered CMOS 256-pixel implantable chip with wide image dynamic range and shared electrodes is proposed and fabricated for subretinal prostheses. The infra-red (IR) light is incident only on photovoltaic cells of the chip whereas the visible light is mainly incident on pixels. The proposed adaptive background cancellation circuit (ABCC) is adopted to increase the image dynamic range so that the subretinal chip can adapt for different surrounding illuminances. Moreover, the bi-directional sharing electrodes (BDSEs) is used to increase electrode size under the same chip area and boost the stimulation charges to 11.4 nC. The functions of the chip have been successfully validated with both electrical measurement and in vitro patch clamp experiments with the retinas of Rd1 mice.