Photovoltaic Effect Essay

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The effect due to which light energy is converted to electric energy in certain semiconductor materials is known as photovoltaic effect. This directly converts light energy to electricity without any intermediate process. For demonstrating the photovoltaic effect let us assume a block of silicon crystal. The upper portion of this block is doped with donor impurities and lower portion is doped with accept or impurities. Hence the concentration of free electrons is quite high in n – type region compared to p-type region and concentration of hole is quite high in p-type region compared to n-type region of the block. There will be a high concentration gradient of charge carriers across the junction line of the block. Free electrons from n-type…show more content…
Across a p-n junction diffusion and drift of charge carriers continues. Diffusion of charge carriers creates and increases the thickness of the potential barrier across the junction and drift of the charge carriers reduces the thickness of the barrier. In normal thermal equilibrium condition and in absence of any external force, the diffusion of charge carrier is equal and opposite of drift of charge carriers hence the thickness of potential barrier remains fixed. Now the n-type surface of the silicon crystal block is exposed to the sunlight. Some of the photons are absorbed by the silicon block. Some of the absorbed photon will have energy greater than the energy gap between valence and conduction band of valence electrons of the silicon atoms. Hence, some of the valence electrons in the covalent bond will be excited and jump out from the bond leaving behind a hole in the bond. In this way electron-hole pairs are generated in the crystal due to incident light. The holes of these light generated electron-hole pairs in the n-type side have enough probability of recombination with enormous electrons (majority carriers). Hence, solar cell is so designed, that the light- generated electrons or holes will not get enough chances to recombine with majority
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