English: Black curve: The limit for the maximum open-circuit current of a solar cell within the Shockley-Queisser model. The x-axis is the bandgap of the solar cell in electron volts, the y-axis is the highest possible open-circuit voltage in volts. The red dotted line is "y=x", showing that the open-circuit voltage is always somewhat smaller than the bandgap voltage. (The model assumes a single-junction solar cell under unconcentrated light, and some other assumptions too. I used the AM1.5G solar spectrum data for the calculation.) I cross-checked my curve with an independently-calculated one and they agree to high accuracy, see Practical Handbook of Photovoltaics p129.