If you look at the cell as a NP device, such as a diode in reverse bias, the following will take place.
When contact is made, electrons can lower their energy by flowing from the semiconductor conduction band into the metal. The resulting build-up of charge on the metal-semiconductor interface causes a deformation of the band structure. This continues until the chemical potential in the semiconductor reaches equilibrium with the Fermi energy of the metal. The deformed band structure forms a potential barrier which electrons must overcome in order to flow from the semiconductor into the metal. In the reverse bias situation, the potential barrier is much greater and the depletion region larger. As a result, very little current flows and voltage will build up until dielectric breakdown occurs!