Solar Cell

NCERT explains that a solar cell is a p-n junction that works on the photovoltaic effect and, unlike a photodiode, is operated with no external bias. When sunlight of energy greater than the band gap falls on the junction, it generates electron-hole pairs, and the built-in field of the depletion region separates them, driving electrons to the n-side and holes to the p-side. This charge separation produces a photovoltage across the terminals, so the cell itself acts as a source of electrical energy without any external battery. The option describing it as a forward-biased diode storing heat is wrong because a solar cell generates electricity from light, not by storing heat, and needs no bias. The option describing it as reverse biased needing an external supply is wrong because the solar cell is a generator, not a device driven by an external source. The option invoking thermionic emission is wrong because that process requires high temperatures and is unrelated to junction photovoltaic action. As stated in NCERT Class 12, Chapter 14, a solar cell generates emf by the photovoltaic effect at an unbiased junction. A consistency check confirms output power rises with illumination, as expected of a light-driven source.