Photovoltaic Cells.

Photovoltaic cells convert light energy into electricity at the atomic level. Although first discovered in 1839, the process of producing electric current in a solid material with the aid of sunlight wasn't truly understood for more than a hundred years. Throughout the second half of the 20th century, the principles underlying the photovoltaic effect have been determined and the manufacturing processes have been more fully refined. As a result, the cost of these devices has put …

…of a top metallic grid or other electrical contact to collect electrons from the semiconductor and transfer them to the external load, and a back contact layer to complete the electrical circuit. Then, on top of the complete cell is typically a glass cover or other type of transparent encapsulate to seal the cell and keep weather out, and an antireflective coating to keep the cell from reflecting the light back away from the cell.