Photovoltaics: A Bright Idea

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Scientists have come up with a seemingly magical way of changing the sun’s energy — not its heat — into electricity. They call the technology photovoltaics — the direct conversion of the sun’s energy into electricity using solar cells thinner than a human hair.

Solar cells do away with all the equipment, boilers, turbines, pipes, cooling reservoirs and towers associated with electrical generation. Within a few microns, photons — packets of energy from the sun — silently energize electrons, which then are pushed by the configuration of the photovoltaic material to flow through attached wires as electricity.

No fuel required — except for the rays of the sun. Containing no moving parts, the panels just silently sit and let photons and electrons interact. Here we have a true revolution in power generation — the first quantum power generator. Science magazine recognized the technology’s unique characteristics when it declared, “If there is a dream technology it is photovoltaics — a space-age electronic marvel at once the most sophisticated solar technology and the simplest, most environmentally benign source of electricity yet conceived.”

The discovery of the first solid-state photovoltaic material occurred in the late 19th century while the earliest worldwide information highway network — transoceanic cables linking the globe to instantaneous telegraphic communications — was being built. Experimenting with bars of selenium, a crystalline material, to detect flaws in the cables as they were submerged, the supervising electrician discovered that the selenium was sun-sensitive.

A published account of the defect led two British scientists to delve more deeply into the relationship of selenium and light. In 1876, they announced their discovery of something completely new: that a solid substance directly converted light into electricity. The scientists called the production of electromotive-power in this fashion “photoelectric,” synonymous with today’s term, photovoltaic.

While Europe’s Edison, Werner von Siemens, in the 1880s considered photoelectricity “scientifically of the most far-reaching importance” and urged a “thorough investigation to determine upon what the electromotive light action of the selenium depends,” few scientists heeded his call. They shied away from examining the photoelectric effect because it seemed to contradict the very underpinnings on which 18th- and 19th-century physics was built. The study of thermodynamics had thoroughly demonstrated that power could be produced only through heat-consuming matter, as seen in a steam machine. In contrast, selenium exposed to light neither absorbed any heat as it produced power nor lost any of its mass.

It required new perspectives from Albert Einstein and other early-20th-century scientists to better explain how selenium — and, for that matter, photovoltaics in general — works when exposed to light.

Light, Einstein explained, consisted of both waves and energized particles, now known as photons, whose power varies by wavelength. Einstein’s novel description of light, combined with the discoveries of electrons and their behavior, gave a clear and scientific explanation: Powerful photons knock weakly glued electrons out of their atomic orbits, and the special make-up of selenium then transfers these freed and energized electrons to flow as electricity.

The material, however, converts far less than 1 percent of all incoming sunlight into electricity — hardly enough to justify its use as a power source. Some therefore summarily dismissed producing electricity for society with photovoltaics. Others judged the discovery as a great breakthrough allowing people to envision “the sun, no longer pouring unrequited into space, but by means of the photoelectric cells its powers gathered into electric storehouses to the total extinction of steam engines and the utter repression of smoke.”

But even the staunchest advocates admitted that the dream could be realized only “if a great deal of further research and development work succeeds in improving their characteristics.”

Work on a completely different material — silicon — resulted in the solar cell earlier researchers had wished for. Calvin Fuller and Gerald Pearson, two scientists at Bell Telephone Laboratories, led the effort that took the silicon transistor, now the principle component in all electrical equipment, from theory to working device. One of the first transistors built by Pearson in 1953 turned out to perform very efficiently as a solar cell. Pearson discovered the attribute when he serendipitously exposed the device, attached to an ammeter, to a sunlit window. To his surprise, the silicon transistor converted almost five times as much electricity from sunlight as had the best selenium cells.

Meanwhile, colleague and friend Darryl Chapin was studying the feasibility of employing freestanding alternative sources of energy, which included solar. No matter what Chapin did, he could not squeeze more energy out of selenium cells than had his predecessors. Hearing of Chapin’s dilemma, Pearson ran down the hall, told him in an excited voice, “Don’t waste another moment on selenium!” and gave him the superior-performing cell. Chapin reproduced Pearson’s finding.

Theoretical calculations of the new cell’s potential were even more encouraging. Under ideal conditions, Chapin discovered, the silicon solar cell could convert a whopping 23 percent of the incoming sunlight into electricity. Showing these figures to his superiors convinced them to change course and have Chapin focus all of his time on refining Pearson’s discovery and creating the world’s first practical solar generator.

After a year of sweat, toil, trying this approach and that and consulting with Fuller, Chapin presented to the world a major breakthrough — the first photovoltaic device capable of converting enough energy directly from sunlight to run everyday electrical equipment.

It was much like “when aircraft went from propeller speeds to jet velocities,” commented a fellow scientist also exploring silicon for power purposes. Others concurred. The New York Times, for example, wrote on page 1 on April 26, 1954, that the work of Chapin, Fuller and Pearson “may mark the beginning of a new era, leading eventually to the realization of one of mankind’s most cherished dreams — the harnessing of the almost limitless energy of the sun for the uses of civilization.”

The Times got it right. The age of modern photovoltaics had begun.

In Part 2, John Perlin looks at how humankind’s frontiers — whether space or the Third World — have proved fertile ground for encouraging photovoltaic use.

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