EES 0837 Lecture Notes - Lecture 30: Polycrystalline Silicon, Amorphous Silicon, Correlation Does Not Imply Causation
3 Apr 2016
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Lecture - 30: solar photovoltaics, making electricity from sunlight, methods of harvesting sunlight, photovoltaic (pv) scheme, highly purified silicon (si) from sand, quartz, etc. is doped with intentional impurities at controlled concentrations to produce a p-n junction. P-n junctions are common and useful: diodes, ccds, photodiodes, transistors: a photon incident on the p-n junction liberates an electron. Photon disappears, any excess energy goes into kinetic energy of electron (heat) Electron wanders around drunkenly, and might stumble into depletion region where electric field exists (electrons, being negative, move against field arrows) Electric field sweeps electron across the junction, constituting a current. More photons more electrons (cid:1) more current (cid:1) more power: provide a circuit for the electron flow, without a path for the electrons to flow out, charge would build up and end up canceling electric field. Pv cell acts like a battery: pv types, single-crystal silicon. Expensive to make (grown as big crystal: poly-crystalline silicon.
