As the applied reverse bias increases, the photodiode current increases sharply. The blocking voltage applied at this point is called the breakdown voltage. This is the maximum applied reverse voltage under which the photodiode should operate (also referred to as the maximum reverse voltage).
If you connect a photodiode with direct polarization (forward bias), it works like a normal diode. However, when a reverse-biased photodiode is used, the amount of electrons flowing through the PN junction is proportional to the amount of light incident on the diode.
In a depletion region, a current is generated due to the absorbed light. This is the amount of electricity proportional to the light intensity. This amount of current corresponds to the leakage current (dark current) + current generated by the photodiode. The dark current is defined depending on how much reverse voltage is applied to the photodiode.