A new installer asks why a silicon module makes DC power in daylight with no moving parts. You explain the cell has p-type and n-type layers forming a junction, photons strike the silicon, and meter leads read voltage and current. Which description correctly explains the photovoltaic effect behind this reading?

The correct description is the photovoltaic effect: absorbed photons generate mobile electron–hole pairs in the silicon, and the built-in electric field at the p–n junction drives the two carrier types in opposite directions. This separation establishes a voltage; when a load completes the circuit, the carriers produce direct current without mechanical motion. A silicon photoconductor also uses light to increase carrier density, but its usual operating principle is that an externally applied field drives current through the illuminated material. It does not explain a module’s self-generated voltage and current through junction-field separation. The Seebeck effect is a genuine way to generate DC without moving parts: a temperature difference produces a voltage in suitable semiconductor junctions. But it converts a heat gradient, not photons generating and separating carriers, so it does not account for the stated light-driven cell operation. A Schottky-barrier solar cell can use photon-generated carriers and a built-in barrier to produce current, but its operative junction is metal–semiconductor, not the stated p-type/n-type silicon junction. Exam caveat: photovoltaic cells can have other architectures, so a mechanism valid for a different cell design need not describe this one. Practical check: measure the module’s open-circuit voltage in light and compare it with the voltage in darkness; light-dependent voltage supports photovoltaic generation, while a thermoelectric signal should track a temperature difference.