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Why are Si and GaAs are preferred materials for solar cells ? |
Answer» Solution :The solar radiation spectrum received by US is shown in figure.  The maxima is near 1.5 eV . For photo -excitation. `hv gt E_(g ) `. Hence, semicondutorwith band gap -1.5eVor lower is likely to give BETTER (in spite of its higher band gap ) than Si because of itsrelatively higher absorption coefficient.If we choose materials like CdS or `CdSe ( E_(g)~ 2.4eV)`,we can use only the high ENERGY component of the solar energy for photo-conversion and a significant part of energy will be no use. The QUESTION arises `:` why we do not use material like pbS ( `Eg ~0.4eV)` which satisfy the condition `hv gt E_(g )` for v maxima corresponding to the solar radiation SPECTRA ? if wedo so, mostof the solar radiation will be absorbed on the top-layer of solar cell and will not reach in or near the deplection region.For effective electron -hole separation,due to the junction field, we want the photo-generation to occur in the junctionregion only. |
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