Solar Cell

Introduction

Solar Cells are used to convert available light into electrical energy. They do this without the use of chemical reactions. This conversion process is based on the work done by a French physicist named Alexander Becquerel in 1839. He discovered the photoelectric effect which describes the release of positive and negative charge carriers in a solid state when light hits its surface. He found, when experimenting with an electrolytic cell made up of two metal electrodes, that some materials would produce small amounts of current when exposed to light.

Fifty years later a scientist named Charles Fritts created the first real solar cell using junctions by coating the semiconductor with a nearly transparent layer of gold. A semiconductor is a material such as silicon or germanium, where the material has properties which fall between conductors and insulators. However the efficiency of this conversion of light to electricity was less than 1 percent.

Next in 1930 a semiconductor was made using copper oxide, yet the efficiency of the conversion was still less than 1 percent. This was overcome in 1954 when silicon was used for the semiconductor and the efficiency was increased to 6 percent. Then by 1989 the use of a device which concentrated light onto the cell surface using a lens, increased the efficiency to 37 percent. This was because of the increased intensity and collected energy on the cell surface.

How a Solar cell works

Semiconductors become conductors when given heat or energy, but are insulators at low temperatures. Over 95% of the semiconductors in the world are made from silicon. This is due to the fact that it is the second most abundant element in the earth’s crust. Therefore it is available in large quantities. To make a solar cell the semiconductor must be doped or contaminated. Doping is intentionally adding chemical elements, which will obtain an excess of positive charge carriers (P-type semi conducting layer) or negative charge carriers (N-type semi conducting layer) from the semiconductor material. If two differently contaminated semiconductor layers are put together then a P-N junction forms on the boundary of the layers.

There are two electrical contact layers, which allow electric current to flow in and out of the cell. The electrical contact layer at the top the top of the cell where the light enters is made of a good conductor, for example a metal. The bottom contact layer must be a very good conductor and is always made of metal.

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Aim

To investigate the factors which influence the output from a solar cell. The factors I am choosing to investigate are the light intensity. This will be how much voltage is supplied, and also the distance of the lamp to the solar cell. I have chosen these because I believe these are the most important factors, and well give us the best results. The results will give us definite results and systematic results, such as a linear graph.

Hypothesis

I predict that as the distance between the lamp and the solar cell the less current the ...

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