Why are Si and GaAs are preferred materials for solar cells?

Explanation

The energy of the maximum intensity of the solar radiation is nearly `1.5eV`. In order to have photo excitation the energy of raditation (hv) must be grater than energy band gap `(E_(g))`. Therefore, the semiconductor with energy band gap equal to or less than `1.5eV` or lower and with higher absorption coefficient, is likely to give better solar covversion efficiency. The energy band gap for Si is about 1.1eV, while for GaAs, it is about `1.53 eV`. The GaAs is better inspite of its higher band gap than Si because it absorbs relatively more energy from the incident solar radiation being of relatively hogher absorption coefficient. We do not use materials having band gap more than 1.5 eV because for such materials most of the solar radiation of energy more than `1.5 eV` are absorbed on the top layer of the solar cell and do not reach in or near the depletion region. Due to it, only a small portion of higher solar energy is used for photoconversion whereas the signific part of the solar energy is of no use.