How Solar Cells Work?

Working of solar cells is based on photovoltaic effect. What is photovoltaic effect? It is a direct conversion of light into electricity at atomic level. This effect was first observed in 1839 by Edmund Bequerel, a French physicist. He had observed that certain materials produced small amounts of electrical energy on being exposed to light. This theory was further studied by Albert Einstein who came up with the theory of photoelectric effect after studying the behavior of light closely. So, now that you know a brief history on solar cells, how they work will be our next subject of study. A solar cell is usually made of a semiconductor material like silicon (most commonly used). In the functioning of a solar cell, it is important to understand as to why silicon is used as a semiconductor material in a solar cell and what is its significance in generating the electrical energy in a solar cell.

Silicon is a non metal with some special chemical properties. If we observe the atomic structure of silicon, it has 14 electrons arranged in three shells. The first two inner shells have 2 and 8 electrons respectively. The outer shell has 4 electrons. As per the atomic structure of any element, the outer shell must contain 8 electrons to achieve a neutrality. So, the silicon atom will devise ways to fill the outer shell with the remaining 4 electrons. Once it bonds with neighboring atoms to complete its outer shell, it gets a crystalline structure. This pure crystalline structure of silicon is such that the electrons are not free to move about. Hence, silicon in pure form is a poor conductor of electricity. So, impurities or other elements like phosphorous are added to it in such a way, that there remain a few electrons which are free to move. The process of adding impurities to silicon is often known as doping. This is because phosphorus has 5 electrons in its outer shell of atomic structure of which 1 electron will be left free. When sun light strikes the silicon semiconductor, the alignment of the atoms is disturbed due to the heat energy of the light. The free electrons present in the semiconductor due to the impurities, break free and move in a particular direction trying to fill in into the holes of crystal lattice structure, thereby generating an electric current. Silicon which is fused with phosphorous to produce this photoelectric effect is also called 'n type semiconductor'.

A solar cell is constituted of two silicon pieces, of which one is the p type semiconductor (the silicon doped with boron) and the n type silicon (the silicon doped with phosphorus). So, when the sun light falls on this solar cell, the p type semiconductor and the n type semiconductor come in contact with each other. In the process, the free electrons in the n type semiconductor rush to fill in the holes in the p type semiconductor. This flow creates the requisite electric current in a solar cell. The electric field produced in the solar cell causes a voltage. Product of the voltage and current is what gives solar power. Voila! That's how a solar cell works.