Photovoltaic cells are made up of

Photovoltaic cells are built from a combination of p type and n type semiconductors.

A p type layer alone cannot generate the needed junction voltage.

An n type layer alone likewise cannot form the working cell.

Having neither p nor n type material would leave no semiconductor to work with.

The p n junction creates an electric field that separates light freed charge carriers.

This flow of separated charges through an external circuit gives the cell its current.