a photovoltaic material
A photovoltaic material is a material that turns sunlight directly into electricity — the working guts of a solar panel. Light goes in, electrical current comes out, with no moving parts.
The mechanism runs on a semiconductor whose band gap is tuned to sunlight. A photon carrying more energy than the gap knocks an electron up from the valence band into the conduction band, leaving behind a positive 'hole'; the built-in electric field of a p-n junction then sweeps the electron one way and the hole the other, and that separated charge is your current. Silicon (band gap about 1.1 eV) dominates the market, alongside thin films such as CdTe and CIGS and the fast-rising perovskites (cheap but not yet stable). A single-junction cell is capped near 33 percent efficiency by the Shockley-Queisser limit.
This matters as a source of clean energy. The honest caveat is why no single material can do the whole job: a photon with less energy than the band gap passes straight through unused, while a photon with much more wastes its excess as heat — so record efficiencies require stacked multi-junction cells, and a real panel (around 20 percent) sits well below laboratory records.
Sunlight hits a silicon solar cell. A photon with more energy than silicon's 1.1 eV band gap knocks an electron up into the conduction band, leaving a positive hole; the built-in field of the p-n junction sweeps the electron one way and the hole the other, and that separated charge is your current. Photons below 1.1 eV pass straight through unused, one reason a single silicon cell caps out near 33 percent efficiency.
A solar cell is a semiconductor whose band gap is tuned to catch sunlight, plus a junction that pulls the charges apart.
No single band gap can harvest the whole solar spectrum — too-low-energy light is missed and too-high-energy light wastes its excess as heat — which is why record efficiencies need stacked multi-junction cells.