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How does the photovoltaic effect produce direct current in a solar cell?

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Diagram of a solar cell showing labeled layers, including a front electrical contact grid, antireflection layer, absorber layer, back junction layer, and back electrical contact layer, with arrows indicating light entering and terminals connecting to a circuit. — solar cell A commonly used solar cell structure. In many such cells, the absorber layer and the back junction layer are both made of the same material.

The photovoltaic effect produces direct current in a solar cell through the interaction of light with semiconductor materials.12

When light strikes the solar cell, photons transfer energy to electrons in the absorber layer, exciting them from a bound "ground state" to a higher-energy "conduction band" where they are free to move. In a uniform material, these electrons would move randomly; however, a solar cell incorporates a junction between dissimilar materials—typically p-type and n-type semiconductors.123

This junction creates a built-in electric field that acts as a force, "tilting" the energy states and forcing the excited electrons to flow in a single, specific direction. This collective motion of electrons toward the electrical contacts and into an external circuit constitutes a direct current (DC). As long as light continues to strike the cell, this process persists, allowing the device to power external electronic loads.12