A single PV device is known as a cell. An individual PV cell is usually small, typically producing about 1 or 2 watts of power. 5 volts, so dozens are wired together into the panels you see on rooftops. The underlying principle is simple: light energy knocks electrons loose. Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially used for electricity generation and as photosensors. This guide explains band gap physics, p-n junctions, cell types, efficiency limits, and 2026 technology trends. Every solar installation starts with a single semiconductor sandwich no thicker than a human.