Solar Cell

A solar cell, also known as a photovoltaic cell, converts light energy directly into electrical energy (an emf) via the photovoltaic effect -- it is essentially a large-area p-n junction designed to generate emf when solar radiation falls on it, rather than to switch or amplify a signal. Solar cells come in p-type and n-type variants: a p-type solar cell uses p-type silicon as its thick base with only an ultra-thin layer of n-type silicon on top forming the junction (n-type cells use the opposite arrangement). The underside of the p-silicon base is coated with metal to form the back electrical contact, while the top n-type layer carries a metal grid as the front electrical contact, topped in turn with an anti-reflection coating and toughened glass to maximise how much incident light actually reaches the junction. When sunlight (photons) is absorbed near the junction, it generates electron-hole pairs exactly as in a photodiode; the junction's own built-in electric field then separates them without needing any external bias -- electrons are swept towards the n-type silicon (collected by the front contact) and holes towards the p-type silicon (collected by the back contact) -- and this separation of charge is itself what develops a potential difference across the cell's terminals; connecting an external load then lets a photocurrent flow through it. Many individual solar cells are wired in series or parallel …