12th Class Physics Sample Paper Physics Sample Paper-2

  • question_answer
    (i) Why are Si and GaAs preferred materials for solar cells?
    (ii) Describe briefly with the help of a necessary circuit diagram, the working principle of a solar cell.


    (i) The energy for the maximum intensity of the solar radiation is nearly 1.5 eV. In order to have photo excitation, the energy of radiation (hv) must be greater than energy band gap \[({{E}_{g}}).\] Therefore, the semiconductor with energy band gap about 1.5 eV or lower than it and with higher absorption coefficient is likely to give better solar conversion efficiency. The energy band gap for Si is about 1.1 eV, 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 radiations being of relatively higher absorption coefficient. (ii) When light of frequency, v such that \[hv>{{E}_{g}}\] (band gap) is incident on junction, then electron-hole pair liberated in the depletion region drifts under the influence of potential barrier. The gathering of these charge carriers make p-type as positive electrode and n-type as negative electrode and hence, generating photo-voltage across solar cell. Circuit diagram

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