Assignment5Solns

These include silicon which dominates the current

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Unformatted text preview: iconductors that are indirect bandgap, since these are poor absorbers of light. These include silicon, which dominates the current photovoltaic industry (and therefore requires 10 ­100 microns of silicon to absorb as opposed to GaAs (direct bandgap) which absorbs it in ~0.2 ­0.8 microns). 3. Stack these in order of increasing bandgap energy, with the highest bandgap on the top of the cell. High energy photons are then absorbed by these semiconductors preferentially and low energy photons are transmitted to underlying layers. The advantage of this is that there is less wasted energy if the photon energy matches the bandgap. Any excess energy over the bandgap is dissipated as heat (phonon emission) and leads to device failure and inefficiency. 4. Package correctly (transparent conductor on top to allow the sun in and a back electrode of high reflect...
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