ENGRI 111 Homework #4 Due Wednesday, October 25, 2006 1) Solar cell A uses a semiconductor with a band gap of 1 eV. Solar cell B uses a semiconductor with a band gap of 2 eV. Either cell is thick enough to absorb all the light above its band gap. Both cells can work simultaneously with one on the top of the other to operate more efficiently in a small space. a) Which cell has to be on top (first to receive the sunlight) for both to work simultaneously? The cell with a larger band gap must be on top in order for both to work simultaneously. In this case solar cell “B” would be on top. b) Why? The photons not absorbed by the top cell can be absorbed by the second cell because of the smaller band gap. Since both cells can work simultaneously the system will be more efficient. 2) In both the conventional solar cell based on p-n junctions and the Gratzel cell, charge carriers are produced by the absorption of light. However the mechanisms for bringing the charge carriers out to current carrying
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