Edmond Becquerel discovered the photovoltaic effect in 1839 by showing that certain materials produce an electrical current when exposed to light. He was nineteen years old at the time, working as an assistant in his father’s physics laboratory at the Museum of Natural History in Paris. His experiment laid the scientific foundation for every solar panel in use today, though it would take 115 years before that foundation turned into practical technology.
The 1839 Experiment
Becquerel’s setup was elegantly simple. He built an electrolytic cell: two metal electrodes placed in a liquid solution that could conduct electricity. When he shone light onto one of the electrodes, the electrical output of the cell increased. The effect was unmistakable. Light was generating electricity.
He tested different types of light and found that blue and ultraviolet light produced the strongest response. He also experimented with coating the electrodes in light-sensitive materials like silver chloride and silver bromide, which boosted the results significantly. His preferred electrode material was platinum, though he noted that silver electrodes also responded to light. By systematically varying these components, Becquerel demonstrated that the phenomenon was real, repeatable, and tied to specific wavelengths of light rather than just heat.
He published his findings in a paper titled “Mémoire sur les effets électriques produits sous l’influence des rayons solaires” (roughly, “Memoir on the electrical effects produced under the influence of solar rays”) in the Comptes rendus de l’académie des sciences, the journal of the French Academy of Sciences.
How a Teenager Ended Up in a Physics Lab
Becquerel’s path to this discovery was shaped almost entirely by his family. His father, Antoine César Becquerel, was a pioneering electrochemist who held the professorship of physics at the Paris Museum of Natural History. At eighteen, Edmond became his father’s laboratory assistant. He never attended a university. Instead, he learned by working alongside one of France’s leading scientists, with direct access to equipment and chemicals that most researchers of his era would have envied.
That family connection mattered. Antoine César’s own work in electrochemistry gave Edmond both the tools and the intellectual framework to investigate how electricity behaved in chemical solutions. The electrolytic cell Edmond used was a standard piece of electrochemistry equipment. His insight was to ask what happened when you added light to the equation. The two later collaborated on several important research publications, and the physics professorship at the Museum of Natural History eventually passed through three generations of Becquerels. Edmond’s son, Henri, would go on to discover radioactivity in 1896.
What He Actually Discovered
What Becquerel observed is now called the photovoltaic effect: the creation of voltage or electrical current in a material when it absorbs light. When photons (particles of light) hit certain materials, they knock electrons loose, creating a flow of electrical charge. Becquerel didn’t have the physics to explain the mechanism at the atomic level, since the electron wouldn’t be identified for another six decades. But he documented the effect precisely enough that later scientists could build on his work.
It’s worth distinguishing this from the photoelectric effect, which Albert Einstein explained in 1905. In the photoelectric effect, light ejects electrons from a material’s surface entirely. The photovoltaic effect is related but distinct: it generates a sustained current within a material or between two electrodes. Becquerel’s discovery is the one that maps directly onto how solar panels work.
From Lab Curiosity to Solar Panels
Becquerel proved that sunlight could produce electricity, but the materials available in 1839 converted only a tiny fraction of light energy into current. For more than a century, the photovoltaic effect remained a scientific curiosity with no practical application. Researchers experimented with selenium-based cells in the 1870s and 1880s, but efficiency stayed extremely low.
The breakthrough came in 1954, when three researchers at Bell Labs in the United States built the first silicon solar cell capable of powering everyday electrical equipment. Silicon turned out to be far better at converting sunlight into electricity than anything Becquerel had access to. That 115-year gap between discovery and application is a reminder that identifying a physical phenomenon and engineering it into useful technology are very different challenges.
Modern solar panels still operate on exactly the principle Becquerel demonstrated as a teenager: light hits a material, and that material produces an electrical current. The scale, efficiency, and materials have changed beyond recognition, but the underlying physics is what a nineteen-year-old observed in a Paris laboratory in 1839.