A field effect cuprous oxide solar cell device based on a gate that controls carrier concentration in semiconductors and using screening-engineered nanostructured electrodes is presented. The cell works in inversion mode, with a top gate that forms a depletion layer and a p-n junction, and with nanostructured electrodes that collect the photocurrent across the junction. This device does not require any doping process or a heterojunction, opening a novel route for materials that are difficult to dope. As a proof of principle, we present experimental results of a silicon field effect solar cell. To demonstrate the potential of this configuration for alternative materials, we present a field-effect solar cell made of earth abundant cuprous oxide, which has a favorable band gap but that is difficult to dope. We show the synthesis of the material, the effect of the gate on the carrier concentration and a photovoltaic power conversion efficiency of 0.2%.