How does a solar cell work?

A solar cell is a specially made photodiode. A process analogous to that happens inside a photodiode, i.e. when visible light is allowed to fall on the p-n junction of a silicon diode bonds in the depletion range break and releases free electrons and holes, happens in the solar cell.

(Photo credit: specmat.com)

These carriers produced ,in the junction of a diode that is not biased by a external potential, gets dragged either ways due to the potential barrier across the junction and the electric field created by this region.

Electrons get dragged to the n side and the holes get dragged to the p side. This leads for an additional potential difference across the junction.

(Photo credit: www.suryaurza.com)

This voltage is called the photovoltage and this process is called the photovoltaic effect.

In this process the electrons that migrated to the n side and the holes that migrated to the p side become the major carriers.

An open circuit voltage (V_OC) of 0.6 V and a short circuit current (I_SC) in the range 30 mA - 50 mA can be obtained from the solar cell under intense solar radiation.

These solar cells are built such that the n region of the cell is thin and the junction has the maximum area. This allows a maximum radiation gain from sunlight to the cell.

(Photo credit : solarserver.com)

To send the electrons collected during the above process and to accumulate the electrons from the outer circuit, electrode systems should be used.

(Photo credit: www.solarcell.net.in)

By connecting these solar cells either in series or in parallel, solar panels can be created.

(Photo credit: ecogreenroofs.co.uk)

However, these solar panels are expensive as the semiconductor used to make them is the single crystal silicon. Present researches prove that other compounds, such as polycrystalline silicon, GaAs, InP can be economical alternatives to the use of single crystal silicon.

(Photo credit: encyclobeamia.solarbotics.net)

Researches also estimate that in the next 20 years, solar cells would be sufficient to provide 10% of the expected energy demand in the world.

(Photo credit: www.treehugger.com)

Action of a transistor

In this note I will present details only about the npn transistor. For those who are interested only on the pnp transistor, you can switch the action of the npn transistor and the behavior of current to adjust with the characteristics of the pnp transistor. (Photo credit: mahasona10000.blogspot.com ) As in the case of a p-n junction,the two n parts of the npn transistor contain an excess of free electrons. In contrast, the p part contains excess holes. As in the case of the p-n junction, in the npn transistor depletion regions develop and junction barriers occur. (Photo credit: daenotes.com) For the correct functioning of the transistor, the first p-n junction is forward biased and the second p-n junction is reverse biased. This results for the first p-n junction to be of low resistance and the second p-n junction to be of high resistance. (Photo credit: www.nzart.org.nz ) The letters of these elements

Gold leaf electroscope

What is a gold leaf electroscope? Gold leaf electroscope is an instrument for detecting and measuring static electricity or voltage. The following diagram shows a modern gold leaf electroscope: Why is gold used to make such an electroscope? Gold is popularly used to make such electroscopes since gold is even sensitive to very minute charges (This is achieved by the malleability of gold - hammering into sheet form and making the mass thin). When we introduce a charged object to the disk of the electroscope ( explained below) we practically do not know the magnitude of the charge. Thus a simple conductor may not be the best option to show a reasonable deflection or response even to minute charges. Thus gold is assumed to be sensitive to charges of any magnitude which makes it more suitable as the indicator. Besides gold is also a non corrosive metal. We practically do not use anhydrous materials inside the glass case. The penetration of

The Silver Mirror Test

What is the Silver Mirror Test? Silver Mirror Test is a test that is used to differentiate between aldose and ketose sugars using the Tollen's reagent. Tollen's reagent is an alkaline solution of ammoniacal silver nitrate and is used to test for aldehydes. *Ketones do not react with the Tollen's reagent. Silver ions in the presence of hydroxide ions form a brown precipitate of silver (I) oxide, Ag 2 O (s) . Ag 2 O This precipitate dissolves in aqueous ammonia, forming the diamminesilver(I) ion, [Ag(NH 3 ) 2 ] + . The reactions that take place in this experiment are as follows: 2Ag + (aq) + 2OH - (aq) → Ag 2 O (s) + H 2 O (l) Ag 2 O (s) + 4NH 3 (aq) + H 2 O (l) → 2[Ag(NH 3 ) 2 ] + (aq) + 2OH - (aq) What happens if Silver Nitrate is used without ammonia or why is ammonia used in this experiment? When ammonia is added to the silver nitrate solution, silver ions are less prone to reduction. Thus, silver is produce

Electromagnetic Induction

What is electromagnetic induction? When an alternative current is allowed to flow through a certain circuit and that circuit is kept near a neutral circuit, the former circuit induces charge distributions in the latter circuit resulting in an induced current in the latter circuit. This phenomenon is called the electromagnetic induction. Thus a potential difference arises across the circuit when exposed to a varying magnetic field. Faraday's law- Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. (Photo credit: gic-edu.com) Thus, fluctuating magnetic fields cause currents to flow in conductors placed within them. This is called induction because there is no physical connection between the conductor and the magnet. The current is said to be induced in the conductor by the magnetic field. In order to produce the maximum force needed for induction, usually the cond

Flame test- By Aditya Abeysinghe

Introduction: Flame test is an experiment used to identify/distinguish metals using colors exposed to a flame. Since metallic halides easily evaporate, the test is usually done using the halide components of metals. Out of the halides, chlorides are frequently used because chlorides give a fast change of color when exposed to the flame as opposed to other halides. Materials needed: · A rod of platinum, nichrome, asbestos or graphite · Concentrated HCl solution · Bunsen burner · Metallic salt (a chloride of a metal) · A cobalt glass (if necessary) Method: Insert the rod of platinum, nichrome, asbestos or graphite into a concentrated solution of HCl. Hold the rod to a Bunsen flame. (to the colorless region) Continue this experiment until the top region of the flame turns colorless. Form a pulp by mixing the metallic salt with the concentrated HCl solution and apply

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