The raw material must be available in abundance and the cost of the material must be low.It must have high electrical conductivity.CuInSe 2 Criteria for Materials to be Used in Solar Cell.The materials which are used for this purpose must have band gap close to 1.5ev. V-I Characteristics of a Photovoltaic Cell If we connect a small load across the junction, there will be a tiny current flowing through it. A voltage is set up which is known as photo voltage. the p-type side of the junction, the p-n junction will behave like a small battery cell. n-type side of the junction and concentration of holes becomes more in another side, i.e. As the concentration of electrons becomes higher in one side, i.e. Similarly, the newly created holes once come to the p-type side cannot further cross the junction became of same barrier potential of the junction. Once, the newly created free electrons come to the n-type side, cannot further cross the junction because of barrier potential of the junction. Similarly, the holes in the depletion can quickly come to the p-type side of the junction. The free electrons in the depletion region can quickly come to the n-type side of the junction. The incident light breaks the thermal equilibrium condition of the junction. The light energy, in the form of photons, supplies sufficient energy to the junction to create a number of electron-hole pairs. When light reaches the p-n junction, the light photons can easily enter in the junction, through very thin p-type layer. We encapsulate the entire assembly by thin glass to protect the solar cell from any mechanical shock. We also provide a current collecting electrode at the bottom of the n-type layer. Just below the p-type layer there is a p-n junction. These electrodes do not obstruct light to reach the thin p-type layer. We then apply a few finer electrodes on the top of the p-type semiconductor layer. A very thin layer of p-type semiconductor is grown on a relatively thicker n-type semiconductor. A solar cell is basically a junction diode, although its construction it is little bit different from conventional p-n junction diodes.
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