The open-circuit voltage, V_oc, is the maximum voltage available from a solar cell, and this occurs at zero current. The open-circuit voltage corresponds to the amount of forward bias on the solar cell due to the bias of the solar cell junction with the light-generated current. The open-circuit voltage is shown on the IV curve below.

IV curve of a solar cell showing the open-circuit voltage.

An equation for V_oc is found by setting the net current equal to zero in the solar cell equation to give:

The above equation shows that V_oc depends on the saturation current of the solar cell and the light-generated current. While I_sc typically has a small variation, the key effect is the saturation current, since this may vary by orders of magnitude. The saturation current, I₀ depends on recombination in the solar cell. Open-circuit voltage is then a measure of the amount of recombination in the device. Silicon solar cells on high quality single crystalline material have open-circuit voltages of up to 730 mV under one sun and AM1.5 conditions, while commercial devices on multicrystalline silicon typically have open-circuit voltages around 600 mV.

The V_OC can also be determined from the carrier concentration:

where kT/q is the thermal voltage, NA is the doping concentration, Δn is the excess carrier concentration and n_i is the intrinsic carrier concentration. The determination of Voc from the carrier concentration is also termed Implied V_oc.