Application of a forward bias to a p–n junction

widens the depletion zone increases the potential difference across the depletion zone increases the number of donors on the n side increases the electric field in the depletion zone.

increases the number of donors on the n side

Number of donors is more because electrons from – ve terminal of the cell pushes (enters) the n side and decreases the number of uncompensated pentavalent ion due to which potential barrier is reduced. The neutralised pentavalent atom are again in position to donate electrons.