Photovoltaic Effect

The photovoltaic effect is the physical phenomenon that makes solar panels work. When photons (particles of light) strike a semiconductor material like silicon, they transfer their energy to electrons in the material, knocking them free from their atomic bonds and creating an electrical current. This direct conversion of light into electricity is the foundation of all solar panel technology.

In a solar cell, the silicon wafer is doped with two different impurities to create a p-n junction — a boundary between positively charged (p-type) and negatively charged (n-type) silicon. When photons free electrons at this junction, the built-in electric field pushes them in one direction, creating a flow of direct current (DC) electricity.

The photovoltaic effect was first observed by French physicist Edmond Becquerel in 1839 and was explained by Albert Einstein in 1905 (for which he received the Nobel Prize). The first practical silicon solar cell was developed at Bell Labs in 1954 with an efficiency of about 6%.

Not all photons can drive the photovoltaic effect. Photons below a minimum energy threshold (determined by the semiconductor's bandgap) pass through without generating electricity. Photons above the threshold generate electron-hole pairs, but excess energy is lost as heat. This fundamental physics limits the theoretical maximum efficiency of a single-junction silicon cell to about 33% (the Shockley-Queisser limit).