Concept:The theoretical efficiency limit for single-junction solar cells (the Shockley-Queisser limit, \( \approx 33\% \)) is constrained by unabsorbed sub-bandgap photons (\( hf < E_g \)) and thermal relaxation of above-bandgap photons (\( hf > E_g \)).
Formula:$$E_{\text{lost}} = (h f - E_g) \quad [\text{for } h f > E_g, \text{ lost as lattice heat phonons}]$$
Solution:- Photons with energies below \( E_g \) (\( 1.1\text{ eV} \) for Si) pass through the material without generating electron-hole pairs.
- Photons with energies above \( E_g \) excite electrons high into the conduction band, where the excess kinetic energy (\( hf - E_g \)) is quickly lost as heat.
- Combined with reflection losses and recombination, practical silicon cell efficiency is limited to roughly \( 18\text{–}24\% \).
Why other options are incorrect:- Option A: Silicon remains conductive under sunlight.
- Option C: Solar cells operate effectively at ambient room and outdoor temperatures.
- Option D: Silicon has a band gap of \( 1.1\text{ eV} \), not an infinite gap.
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