How did the silicon solar cell we use so frequently today got invented? Well it was a long journey and the birth of this great invention needed the brainpower of several scientists before it saw the light of day.

Inventing the solar cell silicon

Photo: Public Domain George Hodan

 

63 years ago a group of scientists were trying to find an alternative to the Traditional dry cellbatteries. These batteries did not work very well in the warmer and more tropic latitudes of the earth. Degeneration of the batteries was too fast, they could simply stop working when you would need them the most. An alternative power source was needed and it was, Daryl Chapin, who got the mission to find this new power source.

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Maybe the thought of the abundance of sun in the tropical parts of the world where the alternative power was needed got the scientists inclined towards solar cells as being a part of the solution. But at the time of this research, the only solar cells that were available in the world were selenium solar cells. These produced way to little power to be considered a good alternative. The selenium cells could only convert less then 0,5% of the caught sunlight into usable power. This only amounted up to 5w/m2

Meanwhile in another corner of the science world

During this same time Gerald Pearson and Calvin Fuller were working on the invention of silicon solid-state devices. Fuller who was a chemist had discovered how to transform silicon which in normal cases conducts electricity very poorly, to be able to conduct in a superior way. Fuller mixed the silicon with a small amount of gallium thus making the metals positively charged. Then when Gerald later on dipped the positive silicon/gallium into steaming hot lithium an area of weakly bound electrons appeared, making the spot negatively charged. After this he shined a light on the whole thing while it was connected to an ammeter. And surprisingly the ammeter showed a great electrical current flowing. This was the birth of the first silicon solar cell.

A true true friend helps a friend in need

Being friends with Daryl Chapin, Gerald and Calvin knew he was working with solar cells and took their new discovery straight to him. After a row of experiments, Chapin discovered that if the new silicon solar cell was exposed to strong sunlight, it performed up to five times as great as the selenium solar cell he was currently using. But he’s theoretical calculations showed that the capacity of the silicon cell could be up to 460% greater than the old cells. Converting a at the time stunning ratio of 23% of the sunlight it got hit with into usable electricity

Inventing problems ahead

But even though he did everything in his power Daryl Chapin couldn’t manage to raise the actual capacity of the silicon solar cell over his initial 25w/m2. The problem according to himself was “making electrical contact to the silicon”. He was not able to solder directly to the solar cell, instead he electroplated a small bits of the differently charged silicon layers. This allowing the electricity to flow out of the silicon solar cell more freely. To Chapin’s frustration no plating would want to stick to the silicon. Thus hindering him from reaching his goal, of harnessing more of the power generated inside the cell.

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This was not his only problem, the silicon cell was at the time highly instable. Because the lithium would wander through the lithium-bathed silicon cell at over room temperature. This resulted in the core of the cell (the p-n junction) moving away from the surface of the solarcell and into the center. This would be closing out much of the light that in another case would be able to hit the p-n junction if it was on the surface like it was supposed to. He needed to find a way to permanently fixate the core atop of the silicon solar cell, so it could convert the maximum amount of photons coming towards it.

 

Together we are unstoppable

Invention of the silicon solar cell

Photo: Public Domain Виталий Смолыгин

Chapin needed help, and he seeked it with his friend Calvin Fuller. Since Calvin hade already did this once but in a different situation. He simply went to find his old notes and copied the procedure. This time Calvin did not dip the silicon in lithium. Instead he vaporized phosphorous onto it. This new method doubled the performance of the solar cell. But still the problem with the contactpoints remained and this frustrated Chapin immensely

It would later be Calvin Fuller who finally resolved that problem. Calvin took a whole new approach to it. He began with silicon just like before, but instead of making it positively charged by adding gallium. He mixed it up with arsenic thus making it negatively charged instead. He then coated the arsenic silicon with a super thin layer of boron. This gave the silicon solar cell a p-n junction very close to the surface of the materials. And not only that, but it was now easy for the team to make stable contact points into the boron-arsenic silicon cells. In this way the finale obstacle had now been resolved and the generated electricity was now possible to extract. All the solar cells built in this way, vastly outperformed the old ones. Chapin now felt it was the time to introduce them to his employees at Bell telephone system and most of all to the world.

 

Showing the world the new silicon solar cell

In 1954 the first solar cell battery was shown at a press conference powering a radiobroadcast. It was foretold that in the future solar powered panels just like this one could out power all the worlds’ coal and oil plants. Here was the new “power photocells intended to be primary power sources.” They had reached a 6% conversion rate “compares favorably with the efficiency of steam and gasoline engines, in contrast with other photoelectric devices which have never been rated higher than 1%.”

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