A solar cell, also called a photovoltaic (PV) cell, consists of several layers of silicon-based material. When photons, particles of solar energy from sunlight, strike a photovoltaic cell, they are reflected, pass through, or are absorbed. Absorbed photons provide energy to generate electricity. The top p-layer absorbs light energy. This energy frees electrons at the junction layer between the p-layer and the n-layer. The freed electrons collect at the bottom n-layer. The loss of electrons from the top layer produces “holes” in the layer that are then filled by other electrons. When a connection, or circuit, is completed between the p-layer and n-layer the flow of electrons creates an electric current. The photovoltaic effect, including the naming of the p-layer and n-layer, was discovered by Russell Ohl (1898–1987), a researcher at Bell Labs, in 1940.