John Perlin Miniseries #8: Photovoltaics: Saved by Silicon

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This eighth entry about the element silicon celebrates the UN’s 2015 Year of Light. We feature John Perlin, author of "Let It Shine: The 6000-Year Story of Solar Energy," who examines at the impact of the semiconductor revolution and its principal material, silicon.Silicon waferIn the last episode Mr. Perlin pointed out that after the Compton Experiment, the reality of Einstein’s photon and the photovoltaic effect, gained universal acceptance in the scientific community.

For those who may have missed an episode in this miniseries, here is what has been published:Author John Perlin Celebrates the Coming Year of LightAuthor John Perlin & the Solar CellThe Pathway to Today’s Solar Revolution: Discovering the Photosensitivity of SeleniumPhotovoltaics Discovered in 1875: Interview with Author John PerlinPhotovoltaic Dreaming: First Attempts at Commercializing PV Einstein: The Father of Photovoltaics Part 1Einstein: The Father of Photovoltaics – Part 2Our last episode ended with an iffy prognosis of the status of photovoltaics made in 1949 when two leading scientists observed: "It must be left to the future whether the discovery of materials more efficient solar cells will reopen the possibility of harnessing solar energy for useful purposes."

Here we interview Perlin on how the future of the solar energy industry was catapulted to its next stage:CleanTechnica: You have pointed out that the semiconductor revolution in the early 1950s laid the pathway for the evolution of photovoltaic technology.Perlin: Yes. The solar cell promising the possibility of a promising clean energy industry arrived quite shortly after the advent of the semiconductor revolution.CleanTechnica: You’re referring to the introduction of silicon? But it once was considered a substandard element.Perlin: For the longest time no one paid much interest in elements like silicon as they were neither good insulators nor good conductors.

Silicon became the semiconductor of choice by the early 1950s because of its better durability and reliability under real world conditions compared to other semiconducting materials.CleanTechnica: You have said early research from telephone giant, Bell Laboratories, proved crucial in the development of PV. Correct?Perlin: Yes. In the late 1940s scientists at Bell Laboratories discovered that by the orderly addition of minute amounts of certain impurities changed them into superior electronic devices, better than anything that existed before.Left to right – Gerald Pearson, Daryl Chapin and Calvin Fuller – the three principle developers of the Bell Solar Battery Image Credit: via AT&T ArchivesBell scientist, Calvin Fuller, discovered how to do just that with silicon in 1952, producing a sandwich with positively charged silicon on one side and negatively charged silicon on the other.

Where the two join a permanent electric force develops. This is the p---n junction – the heart of all semiconductor devicesCleanTechnica: Fuller created something that hadn’t been seen before?Perlin: No one had ever turned silicon into an active semiconducting device before Fuller’s breakthrough. He then taught his colleague Gerald Pearson how to do the same.CleanTechnica: How did solar energy fit into this discovery?Perlin: Silicon prepared this way needs but a certain amount of energy – photons, for example – which lamplight provided in one of Pearson’s experiments to cause positive and negative charges to move to opposite sides of the p-n junction, creating a "solar battery," that converted over six times more light into electricity than did selenium.

CleanTechnica: Bell was seeking alternative power sources?Perlin: It was. Meanwhile, another Bell scientist, Daryl Chapin, assigned to find alternative power sources to run telephones distant from power lines, tried selenium solar cells as one possibility. But the selenium performed dismally as it always had in times past.When Pearson heard about Chapin’s problems with selenium, he ran down the hall to his colleague’s office, shouting "don’t waste another moment on selenium!" and gave him the silicon solar cell he had just tested.CleanTechnica: What happened?Perlin: So began the "Bell Solar Battery" project.

It resulted in a solar cell capable of converting enough sunlight into electricity for practical applications, setting the foundation on which today’s solar revolution has been built.CleanTechnica: How efficient was that solar cell compared to what we deploy today? And will there be a limit to the efficiency of such a cell?Perlin: That will be revealed in the episode to follow.

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