A Brief History of the Photoelectric Phenomenon

In the latter part of the nineteenth century, physicists discovered a new phenomenon. When light is incident on liquids or metallic surfaces, electrons are released. However, no one had an explanation for this bizarre occurrence. At the turn of the century, Albert Einstein provided a theory for this (for which he received the Nobel Prize in physics) and laid the groundwork for the theory of the photoelectric effect. Figure 2.1 shows an experiment that illustrates the photoelectric effect. When light is shone on metal, electrons are released. These electrons are attracted toward a positively charged plate, thereby giving rise to a photoelectric current.

Einstein explained the observed phenomenon by a contemporary theory of quantized energy levels, which had previously been developed by Max Planck. The theory described light as being made up of minuscule bundles of energy called photons. Photons impinging on metals or semiconductors knock electrons off atoms.

In the 1930s, these theorems led to a new discipline in physics called quantum mechanics, which consequently led to the invention of transistors in the 1950s and to the development of semiconductor electronics.

Interestingly, Einstein, who developed the theory of relativity in 1905 (E = m × C2), did not receive recognition until 1929. In essence development solar photovoltaic technology must be credited to him.

The Use of the Photovoltaic Principle in Solar Power Systems

Solar, or photovoltaic (PV), cells are electronic devices that essentially convert the solar energy of sunlight into electric energy or electricity. The physics of solar cells is based on the same semiconductor principles as diodes and transistors, which form the building blocks of the entire world of electronics.

Solar cells convert energy as long as there is sunlight. In the evenings and during cloudy conditions, the conversion process diminishes. It stops completely at dusk and resumes at dawn. Solar cells do not store electricity, but batteries can be used to store the energy. One of the most fascinating aspects of solar cells is their ability to convert the most abundant and free forms of energy into electricity, without moving parts or components and without producing the adverse forms of pollution affecting the ecosystem that are associated with most known methods of producing non-renewable energy, such as fossil fuels, hydroelectric power, or nuclear energy plants.