History of Solar Cells
The history of solar cells involves scientific discovery, invention, and rivalry. We often consider solar power to be a new technology, but it dates back to ancient times.
Humans have been using solar energy for light and heat for hundreds of years. Chinese, Greek, and Roman inventors built structures that tracked the sun to capture light and warmth. Later, concentrated light was applied to ignite fires using curved metallic objects known as 'burning mirrors'. By the 18th century, natural philosophers were trapping solar heat with glass.
First discovered in 1839 by Becquerel, the photoelectric effect is the basis for our ability to harness and convert sunlight into electricity. The idea of generating power from the sun became a tangible prospect for the very first time. The scientific underpinnings of the photoelectric effect were little understood, until Einstein published his 1905 paper explaining the photoelectric effect. It took over 100 years, from the discovery in 1839, for the first solar battery to become a reality.
Once scientists discovered the silicon solar cell, the idea of solar energy began to take off. Solar batteries first powered phone systems in deserts and communication satellites in space. Only later did we see solar cells being used in our homes.
Discovery of the Solar Battery
After Becquerel's discovery, scientists explained the p-n junction using quantum theory and confirmed it through experiments led by Milikan. While Czochralski's work demonstrated the importance of single-crystal semiconductors.
Bell Laboratories was the center of the next big event in solar research. A semiconductor researcher working there discovered a naturally occurring p-n junction in silicon, which had formed due to deformities in the material. The discovery formed the basis of the solar cell.
Daryl Chapin, Calvin Fuller, and Gerald Pearson were responsible for the project. They focused on controlling the properties of semiconductor materials by introducing impurities to silicon. They encountered several problems, such as the migration of the p-n junction away from the light source. Through trial and error, they chose arsenic and boron to create a stable p-n junction.
Thirteen years later in 1954, Bell Labs announced the first silicon solar cell, known as the Bell Solar Battery. The battery was demonstrated by hooking it up to a small toy Ferris wheel and a radio transmitter. The invention caught both the public and media's attention.
Within 18 months, the efficiency of the solar cell had doubled. Despite this, the silicon solar cell was expensive to fabricate. With a 1-watt cell costing in the region of $286, the Bell Solar Battery was not destined for domestic use.
Conflict and Progress
Rivalry and war fueled innovation in the solar industry. The Radio Corporation of America (RCA) was an electronics company known for the introduction and development of radio and television. David Sarnoff, the founder and president, was well-known for being the operator who tapped the message 'THE TITANIC HAS SUNK'. During the Cold War, Sarnoff coined another well-known phrase, 'ATOMS FOR PEACE', which resonated with the public.
In competition with Bell Laboratories, Sarnoff introduced the Silicon Atomic Battery. It ran on photons from Strontium-90, a component of radioactive waste which was later labeled hazardous to human health. Sarnoff arranged a conference at the RCA headquarters to promote the technology. During preparation for the demonstration, the battery was accidentally exposed to sunlight, and it surprisingly worked just as effectively with solar light. Sarnoff and RCA colleagues deliberately drew the blinds to divert attention from the battery's remarkable performance with solar energy.
The Cold War and the Space Race
The space race created an urgent need to improve the efficiency and reliability of solar energy. Within eighteen months, solar efficiency increased from 6% to an impressive 15%.
In July 1955, America revealed the first solar powered satellite as part of Project Vanguard, to be launched in March 1958. The Soviet Union responded by launching Sputnik 1, powered by three silver-zinc batteries, in October 1957. The inclusion of solar cells in these satellites increased the operational potential by months. Solar cells became an integral part of the space program and emerged as the sole source of power. In 1964, solar arrays were used in the first Nimbus Spacecraft launched by NASA. Then in 1966, the space agency commissioned the first orbiting observatory.
During the Cold War, research was not focused on reducing the cost of solar batteries. Therefore, the prospect of domestic solar power in the West was small as other energy sources were well established.
Solar Cell Research
The Post-Cold War Era
In 1968, Dr. Elliott Berman proposed a cell that could be produced using automated process methods, like a photographic film. Exxon corporation provided funding to further research into reducing the costs of solar cells and their manufacture. Berman produced a product suitable for various applications, including roofing materials.
Instead of costly semiconductor-grade silicon, Berman used cheaper wafers that had been rejected by industry. In addition, the fabrication of solar materials for use on Earth was less intensive because they did not need to withstand the extreme conditions found in space.
Cost had been a huge influence on the renewed research agenda, but there was still room for improvement in efficiency and reliability. Despite this research, solar cells were still expensive compared to electricity supplied by power lines. At this time, solar power was mostly used in remote locations and developing countries.
Monocrystalline silicon solar cells represent the first-generation of the technology. While silicon remains the dominant component due to its stability and reputation, new solar materials have been developed.
By the early 2000s, research had turned its focus to new thin film materials. Organic and organic-inorganic hybrids offer the third and fourth generation of solar cells, such as perovskites. Through these new materials, solar cells can be printed onto ultrathin and flexible substrates.
The Future of Solar Technologies
Solar cells are now used in many applications from supplying domestic energy to fibre optic internet. We have huge solar fields generating vast supplies of energy and in the laboratory, emerging technologies can reach efficiencies of around 40%.
In January 2023, a space solar power prototype, MAPLE, was launched into orbit. MAPLE has been used to harness sunlight in space and send the power to Earth in an uninterrupted beam. This is an important improvement over the intermittent power supply of solar technologies on Earth. The success of the prototype offers the promise of a continuous energy source in the future.
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Professional Science Writer