The first practical photovoltaic cell was developed in 1954 at Bell Laboratories [5] by Daryl Chapin, Calvin Souther Fuller and Gerald Pearson. They used a diffused silicon p–n junction that reached 6% efficiency, compared to the selenium cells that found it difficult to reach 0.5%.[6] Les Hoffman CEO of Hoffman Electronics Corporation had his Semiconductor Division pioneer the fabrication and mass production of solar cells. From 1954 to 1960 Hoffman improved the efficiency of Solar Cells from 2% to 14%. At first, cells were developed for toys and other minor uses, as the cost of the electricity they produced was very high; in relative terms, a cell that produced 1 watt of electrical power in bright sunlight cost about $250, comparing to $2 to $3 per watt for a coal plant.
Solar cells were brought from obscurity by the suggestion to add them, probably due to the successes made by Hoffman Electronics, to the Vanguard I satellite, launched in 1958. In the original plans, the satellite would be powered only by battery, and last a short time while this ran down. By adding cells to the outside of the body, the mission time could be extended with no major changes to the spacecraft or its power systems. In 1959 the United States launched Explorer 6. It featured large solar arrays resembling wings, which became a common feature in future satellites. These arrays consisted of 9600 Hoffman solar cells. There was some skepticism at first, but in practice the cells proved to be a huge success, and solar cells were quickly designed into many new satellites, notably Bell's own Telstar.