In an unbiased p-n junction (no battery connected), which side is at the higher electric potential?
When the junction forms, electrons diffuse from the n side to the p side and holes the other way. They leave behind fixed positive donor ions on the n side and fixed negative acceptor ions on the p side, forming the depletion region.
The positive ions put the n side at the higher potential, by the barrier potential of a few tenths of a volt. That built-in barrier is what stops further diffusion, and it exists even with no battery connected.
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