7. Solar cell A uses a semiconductor with a band gap of 1 eV. Solar cell B uses

Question

7. Solar cell A uses a semiconductor with a band gap of 1 eV. Solar cell B uses a semiconductor with a band gap of2 eV. Either cell is thick enough to absorb all the light above its band gap. Both cells can work simultaneously with one on top of the other to operate more efficiently. But which cell has to be on top (first to receive the sunlight) for both to work simultaneously and why? 8. A compound has the following band diagram, with the shading representing occupancy by electrons: The solid has a completely filled lower energy band and a partially filled higher energy band. a. Predict the electrical properties of this solid on the basis of its band diagram (metal? Semiconductor? Insulator?) b. What would happen to the electrical properties of this compound if all of the electrons were removed from the conduction band and why? Would you use a chemical oxidizing agent or reducing agent to accomplish this and why?

Explanation / Answer

8. A. From the band diagram it is predicted that it is a metal. As lower energy valence bond is filled and next higher energy conduction band is also half-filled. So it will act as a metal.

b. Now if all the electrons will be removed from the conduction band then the gap will increase and there is no electron density in the conduction band. SO it will act as a semiconductor then.

And Electron goes from metal so metal turns into positive charge so it will act as an oxidizing agent that means it will oxidize others but take up electrons and by itself reduced. To accomplish it we should use a reducing agent which can give the electrons and by reducing the metal positive charge and make it neutral.

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