Fill factor

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Fill factor in the context of solar cell technology it is defined as the ratio (given as percent) of the actual maximum obtainable power, (V_mp x I_mp) to the theoretical (not actually obtainable) power, (I_sc x V_oc).

1. The open circuit voltage (V_oc) is the maximum voltage, when the circuit resistance has caused any current to cease flowing.
2. The short circuit current density (I_sc) is the maximum current through the circuit when there is no resistance (and hence no voltage).
3. The fill factor (FF), is thus defined as (V_mpI_mp)/(V_ocI_sc), where I_mp and V_mp represent the current density and voltage at the maximum power point, this point being obtained by varying the resistance in the circuit until I x V is at it's greatest value.

[edit] Other uses of the term

In vision science, the fill factor is the ratio of view areas to the object visible areas.

For optical micro-lens arrays, the fill factor is defined as the ratio of the active refracting area to the total contiguous area occupied by the lens array.