Milestones:First Practical Photovoltaic Solar Cell
First Practical Photovoltaic Cell, 1954
At Bell Telephone Laboratories in Berkeley Heights, NJ, Daryl Chapin, with Bell Labs colleagues Calvin Fuller and Gerald Pearson, invented the first practical photovoltaic solar cell for converting sunlight into useful electrical power at a conversion efficiency of about six percent. It was first demonstrated on April 25, 1954 and led to the development of photovoltaic solar panels used to power virtually all satellites starting with the Vanguard 1 in March 1958 and then later to power the many photovoltaic solar cell energy systems in use today. This invention was the prototype of present photovoltaic cells that are in widespread manufacture all over the world and is a key element of the renewable energy effort to reduce the use of fossil fuels to combat global warming. This invention was quickly recognized for its importance and was put into application as the source of power for Telstar, the first commercial communications satellite.
The following excerpt copied from Wikipedia, Solar Cell, History Of Solar Cells, ref. , also confirmed with more detail by ref. .
“The photovoltaic effect was first recognized in 1839 by French physicist A. E. Becquerel. However, it was not until 1883 that the first solar cell was built, by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions. The device was only around 1% efficient. Sven Ason Berglund had a number of patents concerning methods of increasing the capacity of these cells. Russell Ohl patented the modern junction semiconductor solar cell in 1946, which was discovered while working on the series of advances that would lead to the transistor.”
The following is a summary of development efforts at Bell Labs leading to the invention and demonstration of the ‘Bell Solar Cell’ on April 25th, 1954, taken from reference  Chapter 3, ‘The Dream Becomes Real’.<span id="fck_dom_range_temp_1249171565828_234" />
In the very early 1950s at Bell Labs, Calvin Fuller and Gerald Pearson led the pioneering effort that developed the silicon transistor from theory to a practical working device. Fuller was characterized as the experimentalist while Fuller, a chemist, learned how to control the addition of impurities that would transform silicon into good semiconductor devices. During one of their experiments with gallium doped silicon which was then treated with a lithium bath, they had inadvertently developed a pretty good solar cell. In sunlight with wires connected to the p-n junction, Pearson recorded a significant current.
While Fuller and Pearson continued to work on improving transistor devices, another Bell Labs colleague, Daryl Chapin began work on providing small amounts of power in humid conditions as they were having difficulty maintaining energy in dry-cell batteries in humid locations. Chapin suggested the investigation of solar cells in his work which was approved and which started in February of 1953.  He started his work by testing a commercial selenium cell and found that it only had an energy efficiency of about 0.5 percent.
When Pearson heard of Chapin’s disappointing solar cell work with selenium, he suggested switching to silicon and gave him a silicon solar cell that he had been testing. It was measured by Chapin as having an efficiency of 2.3 percent. As it was much better than selenium, he dropped selenium and concentrated on improving the silicon cell with a goal to reach an efficiency of 5.7 percent. After months of work he had not been able to improve the first silicon cell that Pearson had given him. One problem was making good electrical contact with the silicon and another was that lithium could migrate further into the cell at room temperature and therefore move the p-n junction further away from the surface.
Chapin then guessed that the p-n junction should be near the surface and turned to Fuller for advice. Fuller, two years earlier, had made a device with the junction close to the surface and offered to make some samples. These were phosphorous vaporized onto positive silicon. However, after a month of work with poor results he had a hunch that the shinny surface was reflecting the sunlight rather than absorbing it. Therefore he coated the cell with dull plastic coating and got an energy conversion efficiency of about 4 percent.
About this time RCA made a big media announcement that it had developed a nuclear powered silicon cell to coincide with the Atoms for Peace program initiated by President Eisenhower. It used photons from strontium-90 to activate current flow across a p-n junction. This caught the attention of Bell Labs management and put pressure on the solar cell research team to produce results. Fuller came up with better cells by cutting long strips modeled after Chapin’s best performing cells. Then he used arsenic to give the silicon a negative charge and used boron to create a thin positive top layer. Three samples were treated with the dull plastic coating and tested and one achieved an energy efficiency of nearly six percent in early 1954.
On April 25th, 1954, Bell executives presented the ‘Bell Solar Cell’ to the public with a display of cells using only sun power to operate a 21 inch Ferris Wheel. It was also pointed out in the press about that time that with the Bell solar cells linked together could deliver power at the rate of 50 watts per square yard while the RCA atomic cell delivered only a millionth watt over the same area, a difference of 50 million.
This ends the of summary of development efforts at Bell Labs leading to the invention and demonstration of the ‘Bell Solar Cell’ on April 25th, 1954, taken from reference  Chapter 3, ‘The Dream Becomes Real’.
References and Further Reading
1. Wikipedia, Solar Cell, http://en.wikipedia.org/wiki/Solar_cell
2. Encyclobeamia,Solar Cell Article, http://encyclobeamia.solarbotics.net/articles/solar_cell.html
3. National Inventors Hall of Fame, Daryl M. Chapin, Inducted into in 2008 http://www.invent.org/2008induction/1_3_08_induction_chapin.asp
4. From Space to Earth, The Story of Solar Electricity, by John Perlin, 1999, 2000, First Harvard University Press Edition 2002.
5. Solar Energy Handbook, Jan F. Krieder, Ed. In Chief, and Frank Kreith, Chapter 24, Photovoltaic Solar Energy Conversion Systems, p.24-2, History.