Simple Theory to See that an Optimum Energy Gap Exists

Suppose a two-level device is illuminated by a distribution of dE photons in energy range (E, E + AE). Expressing n  

For each distribution of radiation this yields the energy gap, 

Let solar energy be incident at intensity (j) (power per unit area). Then a cell of area A and efficiency r) will yield power 

Suppose the cell costs K dollars or k = K/A dollars per unit area. Then the price fo the cell in dollars per peak watt is 

The right-hand side has clearly the unit dollars per m which 30 

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II) Simple theory to see that an optimum energy gap exists... 

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