Two identical p-n junctions may be connected in series with a battery in three different ways as shown in fig. The potential difference across the, two p-n junctions are equal in circuits

The potential drop across p-n junction is equal when either both the junctions are forward biased, or both are reverse biased. Since in the second circuit, both the p-n junctions are reverse biased.

The potential difference across the two p-n junctions is equal in circuits (b) and (c).