1873-1876: Selenium Shown to be Photoconductive, Generates Electricity Using Sunlight

Scientist Willoughby Smith discovers the photoconductivity of selenium. Photoconductivity can be defined as an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation. Three years later, William Grylls Adams and Richard Evans Day discover that selenium produces electricity when exposed to light. The cells constructed by the two scientists do not convert enough sunlight to power electrical equipment, but they do prove that a solid material can change light into electricity without heat or moving parts. [US Department of Energy, 2002 ; Allison June Barlow Chaney, 2011]