Ratio of the real maximum output power,
\(P_{\rm{max}}\), that can be obtained with an actual
solar cell to the product of the open-circuit potential,
\(V_{\rm{oc}}\), and short-circuit photocurrent,
\(I_{\rm{sc}}\):
\[f_{\rm{FF}} = P_{\rm{max}}/V_{\rm{oc}}I_{\rm{sc}}\]Note:
The \(P_{\rm{max}}\) value is obtained from the cell volt-ampere characteristic as the maximum of the product \(V\!\cdot\!I = P\). Note that the product \(V_{\rm{oc}}\!\cdot\!I_{\rm{sc}}\) is not a theoretical maximum output power of the cell, since the product is zero at both these values as \(I = 0\) for the open circuit and \(V = 0\) for short circuit.
Source:
PAC, 2022, 94, 15. 'Glossary of terms relating to electronic, photonic and magnetic properties of polymers (IUPAC Recommendations 2021)' on page 33 (https://doi.org/10.1515/pac-2020-0501)