Stable cycling behavior of the light invariant AlGaAs/Si/metal hydride solar cell

The extended stability (eight month) of an unusual solar cell which provides a nearly constant energetic output in illuminated or dark conditions is demonstrated. Bipolar multiple bandgap semiconductors are selected to provide a high photopotential and efficient conversion of insolation. A redox couple is chosen with an electrochemical potential closely matched to the photopotential, and provides efficient high-capacity electrochemical storage. The single cell combines bipolar AlGaAs (Eg=1.6 eV) and Si (Eg=1.0 eV) and metal hydride/NiOOH storage, and generates a light variation insensitive potential of 1.2–1.3 V at an overall solar conversion efficiency of 18.2%. The cell generates power under illumination and in the dark, and in the dark stored energy is spontaneously (without external switching) released.