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During the winter, the inside of an average house is maintained at 20 ºC, while the outside temperature is 0 ºC. Assuming that the only mechanism of heat transfer is conduction, the walls are 10 cm thick and the heat conductivity of the walls is \(0.5 W/Km\). Calculate the heat flux from the room to the surroundings in \(W/m^2\).We decide that, to reduce the heat loss through the walls, the material should be changed to an insulator material. The new overall conductivity will be \(0.1 W/Km\), and the thickness of the wall is maintained. Calculate the reduction of the heat flux throughout the walls in % compared to the initial case. ______

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The figure below shows the band diagram of a tandem cell based on an amorphous and a microcrystalline silicon junction. In which position (A, B, C or D) are the electrons and holes, generated in the microcrystalline silicon junction, collected?

A. The holes are not collected at position A, B, C and D, but recombine with a light excited electron from the top cell at the recombination junction. The electrons are collected at
B. The holes are collected at D and the electrons at
C. The holes are collected at C and the electrons at
D. The holes are collected at D and the electrons at A, B, C or

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Consider a p-i-n a-Si:H solar cell. The various films are, from top to bottom: ZnO, a-Si:H (p-i-n), ZnO and Ag. Which deposition technologies and in which chronological order (from first processing step to the last processing step) are used to process the solar cell?

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Why can't an a-Si:H solar cell rely on diffusion to separate the photogenerated carriers as much as a c-Si solar cell does?

A. The higher bandgap (around 1.7 eV) prevents the photogenerated carriers from diffusing through the intrinsic layer of the a-Si:H cell.
Because the absorption coefficient of a-Si:H is 70 times higher than that of c-Si in the visible region of the solar spectrum.
C. Because the diffusion length is around 300 nm, while in c-Si it is around 300 microns.

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In the figure below the bandgap versus the lattice constant of various materials is shown.Which of the following statements is true?

A. The junctions of a lattice-matched triple junction solar cell can be based on the semiconductor materials GaInP, GaAs and Si.
B. If the bottom cell of a 4-junction cell is based on Ge, the first junction above the bottom cell is based on GaInAs.
C. A combination of three junctions based on the semiconductor materials GaInP, GaAs and Ge can only result in a metamorphic triple junction solar cell.
D. The semiconductor material InAs is a logic choice to be used as a top cell in a triple junction.

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