why are GaAS and si are preferred materials for solar cells? The NCERT explanation is not clear..please explain it .... please ANSWER SOON..
The energy of the sun rays should always be more than the amount of energy required for photo excitation. The maximum solar irradiance intensity(energy) is equal to 1.5eV. So in order to get better Solar Efficiency we should use a material which need excitation energy less than 1.5eV. Now Si has band gap Eg = 1.1eV and GaAs has Eg = 1.53eV. Here Eg of GaAs is more than 1.5eV but we still use it a solar cell material because it has higher absorption coefficient.
Eg for Si is 1.1 and for GaAs is 1.53
For photo excitation energy hv has to be greater than Eg
According to the graaph, maxima is at 1.5
So substances with Eg less than 1.5 is suitable
That is why si and gaas are preffered. GaAs is having Eg more than 1.5 but it has higher absorption co efficient.