Question

Explain, using your own words, how a solar cell works. Please include the description of all relevant physical processes, such as charge carrier generation, recombination, and collection. Include a descriptionof carrier concentration upon illumination.

Length should be 1 page ,12 font, single spaced.

Answer 1

A solar cell is a solid state electrical device (P-N junction) that converts the energy of light directly into electricity using the photovotaic effect.when light reaches to the P-N junction,the light photons can easily enter in the junction.The light energy supplies sufficient energy to the junction to create a number of free electon-hole pairs.The free electrons in the depletion region can quickly come to the N-type side of the junction and holes come to the P-type side of the junction. The holes and electrons cannot further cross the junction because of barrier potential of the junction.As the concentration of electrons becomes higher in one side and concentration of holes becomes more in another side the p-n junction will behave like a small battery cell.A voltage is set up which is known as photo voltage.If we connect a small load across the junction, there will be a tiny current flowing through it. Single-crystal silicon is the most frequently used, bestunderstood material for solar cells.A typical pn-junction single-crystal silicon solar cell has several layers : a conducting grid on the top surface; an antireflective coating and/or treated surface layer; a thin layer of usually n-type silicon about one micrometer thick (called the collector); a very narrow junction-field region where there are almost no free charge carriers; a silicon base layer, oppositely doped to the collector (usually p-type); and a back-contact electrode. Some of the sunlight that strikes a solar cell is reflected.This would be a horrendous loss in terms of efficiency.Fortunately,there are several ways of treating cell surfaces to cut reflection drastically. Among them are chemically coating and texturing the surface.What happens to light entering a cell? It can go through (a), can be absorbed as heat (b), can generate an electron-hole pair (c), or can generate an electron-hole pair and have excess energy that is lost as heat (d). Recombination of electrons and holes are due to Light-generated electrons and holes (empty bonds) that randomly encounter each and also brought together by surface and material defects in the cell.A PV cell contains a barrier that is set up by opposite electric charges facing one another on either side of a dividing line.This potential barrier selectively separates light-generated electrons and holes, sending more electrons to one side of the cell, and more holes to the other.