Solar-cell fill factor ($\mathrm{FF}=P_{\max }/(V_{\mathrm{oc}}{I}_{\mathrm{sc}})$)

The solar-cell fill factor compares the maximum delivered electrical power with the rectangle formed by the open-circuit electric potential difference and short-circuit electric current. It measures the shape of the illuminated current-voltage characteristic. The conversion efficiency is $\eta =V_{\mathrm{oc}}{I}_{\mathrm{sc}}\mathrm{FF}/P_{\mathrm{in}}$.