SOLAR CELL FABRICATION,SOLAR CELLS,

PHOTO VOLTAIC GENERATORS

As name indicates PHOTO = light VOLTAIC = volts PHOTVOLTAICS IS A METHOD of generating

electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the Photovoltaic effect.

WHAT IS PHOTO VOLTAIC EFFECT?

Photovoltaic effect is the basis of photo voltaic power generation.

The photovoltaic effect is the creation of voltage or electric current in a material upon exposure to light.

PHOTO VOLTAIC GENERATION

WHAT IS PHOTO VOLTAIC EFFECT?

• When the sunlight or any other light is incident upon a material surface, the electrons present in the valence band absorb energy and, being excited, jump to the conduction band and become free. These highly excited electrons jump into a different material (electrodes). This generates an electromotive force, and thus some of the light energy is converted into electric energy which means energy is generated in this way.

FABRICATION OF SOLAR/PHOTOVOLTAIC CELL

In 1883, first photo voltaic cell was made by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions.

It was only 1% efficient. To understand the fabrication of solar

cells we need to understand some basics,……….

FABRICATION OF SOLAR/PHOTOVOLTAIC CELL

Basically A solar cell is a junction (usually a PN junction) with sunlight shining on it.

FABRICATION OF SOLAR CELLS

The first practical photovoltaic cell was developed in 1954 at Bell Laboratories .They used a diffused silicon p–n junction that reached 6% efficiency, compared to the selenium cells.

Most practical solar cells are silicon based , because it is cheap and abundant material.

STEPS OF FABRICATION

First step is refining silicon Silicon dioxide (SiO2) is the most abundant

mineral in the earth's crust. The manufacture of the hyper pure silicon for

photovoltaics starts with locating a source of silicon dioxide in the form of sand.

The silica is reduced (oxygen removed) through a reaction with carbon in the form of coal, charcoal and heating to 1500-2000 °C in an electrode arc furnace.


oSilicon di oxide + Carbon = Silicon + Carbon di oxide

oThe resulting silicon is 98% pure. It contains Fe, Al, and B , to remove these traces , further purification is done , Powdered Si is reacted with anhydrous HCl at 300 °C to form SiHCl3


• During this reaction impurities such as Fe, Al, and B react to form their halides (e.g. FeCl3, AlCl3, and BCl3).

• The SiHCl3 has a low boiling point of 31.8 °C and distillation is used to purify the SiHCl3 from theimpurity halides.

• Finally, the pure SiHCl3 is reacted with hydrogen at 1100°C for ~200 – 300 hours to produce a very pure form of silicon.


Above reaction takes place inside large vacuum chambers and the silicon is deposited onto thin polysilicon rods (small grain size silicon) to produce high-purity polysilicon rods of diameter 150-200mm.

Silicon used for solar cells can be single crystalline, multi crystalline, polycrystalline or amorphous. The key difference between these materials is degree to which the semiconductor has a regular, perfectly ordered crystal structure.


AFTER GETTING THE REQUIRED SILICON FROM ABOVE MENTIONED CHEMICAL PROCEDURE , different methods of solar cells fabrication are applied , each method involves doping of silicon to make p-n junction , and required processes to make a furnished solar cell.

METHODS OF FABRICATION

1) SCREEN PRINTED SOLAR CELL FABRICATION TECHNOLOGY

Screen-printed solar cells were first developed in the 1970's. Most mature solar cell fabrication technology. The key advantage of screen-printing is the relative simplicity of the process.

It involves cutting a wafer of 10*10 square cm

,0.5mm thick , this wafer is then p-type doped with born to add up holes .

SCREEN PRINTED SOLAR CELL FABRICATION TECHNOLOGY










1) SCREEN PRINTED SOLAR CELL FABRICATION TECHNOLOGY




BURIED CONTACT FABRICATION TECHNOLOGY

BURIED CONTACT FABRICATION TECHNOLOGY

The buried contact solar cell is a high efficiency commercial solar cell technology based on a plated metal contact inside a laser-formed groove.

Buried contact solar cell to have performance up to 25% better than commercial screen-printed solar cells.

Shading losses are 2 to 3%. without having a wide strip of metal on the

top surface as in last case, and a large metal height-to-width aspect ratio increases the efficiency of cell.

RECENT FABRICATION RESEARCHES

To further increase efficiencies of solar cells , it is found useful to modify the structures of solar cells

to maximize the life of cells as well as to increase their power rating .

Some new structures are shown next……

RECENT IMPROVEMENTS

USE OF SOLAR CELLS FOR SPACE VEHICLES

Invention of solar cells for practical scales and their implementation for power generation in space vehicles has modified and eased the space research work.

Solar panels are shaped and fixed on the body of space vehicle .

Sine sun rays need no any medium to flow , these rays are available in space and are utilized by solar cells for power requirements of space vehicles.

So in space vehicles , D.C batteries are only used for power storage , and they are not the only source of power generation , as solar cells are installed

USE OF SOLAR CELLS IN SPACE FOR EARTH

The solar energy available in space is literally billions of times greater than we use today.

Americans are working on to gathers energy from sunlight in space and transmits it wirelessly to Earth i.e. SPACED BASED SOLAR POWER PROJECT

Space solar power is by far the largest potential energy source available.

A lot of work is to be done in this context.

USE OF SOLAR CELLS IN SPACE FOR EARTH

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SOLAR CELL FABRICATION,SOLAR CELLS,