For this week’s set of experiments in our poll we will stick to the 19th century. Our first entry is from 1839, when Alexandre Edmond Becquerel invented the photovoltaic cell at the tender age of 19. While playing around in his father’s lab, Becquerel created an electrolytic cell from silver chloride in acid. After connecting it to platinum electrodes, he found that exposing it to light generated an electrical current. Currently, photovoltaics is one of the most active themes in materials research, as it may be key in our challenge to produce enough clean energy for the world for generations ahead.