The HPEV cell's extra back outlet would allow the current to be split into two, so that one part of the current contributes to solar fuels generation, and the rest can be extracted as electrical power.

A Solar Cell That Does Double Duty for Renewable Energy

Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory and the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, have developed an artificial photosynthesis device called a “hybrid photoelectrochemical and voltaic (HPEV) cell” that turns sunlight and water into two types of energy – hydrogen fuel and electricity.

Berkeley Lab News Center