![]() However, when we put the p-type and the n-type materials in contact with each other, something interesting (and useful) happens. Through doping, and the resulting changes in electronegativeity, silicon is turned into a conductor of electricity (albeit not a particularly good one). This is known as electronegativity-a measure of how strongly an atom or material hangs on to its electrons. This gives each doped material an overall slight preference to either give or receive electrons. The extra electrons and holes can float around the lattice they are ‘shared’ by all the atoms in the structure. When silicon is doped with elements that have fewer electrons in their outermost shell, it produces a p-type material. We now have a material with an overall deficiency of electrons, making a positive (p-type) material. This movement also constitutes an electrical current. Alternatively, the holes themselves can be thought of as moving (in the opposite direction to the electrons) as the electrons hop from one bond to another. Electrons within the boron-doped silicon can jump around to fill in the hole. This leaves one of the bonds with only one electron, creating a ‘hole’ in the bonding structure. We can also dope with boron, which has only three electrons in its outer shell. When silicon is doped with elements that have extra electrons in their outermost shell, it produces an n-type material. Electrons have a negative charge, so when the silicon is doped in this way, it’s called a negative material: n-type. Adding small amounts of phosphorus, which has five electrons in its outer shell, as compared with silicon’s four, means that the extra (fifth) electron has nothing to bond to, so it’s free to roam around and create electric current. Because of the arrangement of bonds in its crystal structure, silicon in its pure form doesn’t have very many free electrons, so we ‘dope’ it.ĭoping adds an impurity to the silicon to change the way its atoms are bonded together and share their electrons. That’s what electricity actually is, after all-the flow of electrons. This bonding mechanism means there are very few free electrons floating about, which is what we need to create electricity. The outermost electrons in silicon atoms form covalent bonds with each other, creating a lattice structure. This means that it makes perfect covalent bonds with four other silicon atoms, forming a lattice structure. Silicon is special because of the arrangement of its electrons-it has four out of the possible eight electrons in its outermost shell. Most photovoltaic cells are made of silicon, an element that is at the heart of all modern electronics. Photovoltaic cells are based on a related phenomenon called the photovoltaic effect, and they convert light directly into electricity. In 1921, Einstein received the Nobel Prize for his work explaining this. It has been known for more than 150 years that light can have an effect on the electrical properties of some materials. Image source: Marufish / Flickr.īut how exactly does it work? How can sunlight be made to power cars, or to produce the electricity we need for our computers, TVs and toasters? ![]() Photovoltaic solar cells, such as those in these rooftop panels, convert light directly to electricity. Solar panels are appearing on more and more rooftops around our suburbs as solar photovoltaics (PV) become an increasingly viable option for domestic electricity production. ![]() Many years of solid work have seen that rise to generally around 20 per cent. That first solar cell had an efficiency of around 5 per cent. The first practical silicon photovoltaic cell was developed by Daryl Chapin, Calvin Fuller and Gerald Pearson at Bell Laboratories in 1954. Since the demonstration of the first silicon photovoltaic cell in 1954, by Daryl Chapin, Calvin Fuller and Gerald Pearson at Bell Laboratories, New Jersey, we have been refining the technology that enables us to harness the reliable, free and clean energy from the Sun. They’ve also utilised it indirectly-through photosynthesis to power the plant growth underpinning the agriculture that supplies us with food and the oxygen we breathe.Īnd there is another way to use this abundant energy source: photovoltaic (photo = light, voltaic = electricity formed through chemical reaction) solar cells, which allow us to convert sunlight directly into electricity. Humans have always used some of the Sun’s energy directly-for drying clothes and foodstuffs, for example. GLOSSARY primary energy Energy in natural sources that has not been converted into other forms by humans. This is a lot-around 6,200 times the amount of commercial Earth is bathed in huge amounts of energy from the Sun-885 million terawatt hours every year. ![]()
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