1940: Bell Lab Researcher Inadvertently Discovers ‘P-N Junction,’ Basis of Modern Solar Cells

Semiconductor researcher Russell Shoemaker Ohl of Bell Laboratories is poring over silicon samples, one of which has a crack in the middle. Electrical current flows through the cracked sample when exposed to light. The crack, likely formed when the sample was made, actually marks the boundary between regions containing different levels of impurities, so one side is positively “doped” and the other negatively doped. Ohl has inadvertently created a “p-n junction,” the basis of a solar cell. When an excess positive charge builds up on one side of the p-n barrier, and a similar excess charge builds up on the other, negatively charged side, an electric field is created. The cell can be hooked up into a circuit, and incoming photos striking the cell can “kick” electrons loose and start a current flowing. Ohl patents the solar cell, which operates at about one percent efficiency. [American Physical Society, 2013]