Multiple choise questions related to lecture PV2

What is fermi level? The electron hole pair energy in equilibrium state An average energy of an electron in the conduction band The energy of the electron-hole pair right after the photon’s energy is absorbed The electrochemical potential of electrons A level of understanding much higher than what is necessary for passing this course

What is a majority carrier? An electron that has entered the p-type material, or a hole that has entered the n-type material A free electron in an n-type material, for example Both answers above are false

Which factor determines the conductivity of a p-type semiconductor? Amount of electrons Fill factor Membrane permeability Amount of holes Index of refraction Lifetime of carriers

What can be found at the depletion region? Free charge carriers Superlattices Ionized donor or acceptor impurities d) Valence electrons e) Magnetic monopoles f) Antiprotons

How is the depletion region formed? When a current is applied to the p-n junction Through diffusion and drift of electrons and holes When an outer electric field is applied to the p-n junction

Why do holes diffuse from p-type to n-type semiconductor? Because of the electric field within the depletion layer Because of the difference in concentration of carriers Because of the difference in the electrostatic potential

In p type semiconductor the Fermi level lies closer to… conduction band edge valence band edge Neither above, as it lies directly in the middle of conduction and valence band edges.

What is a phonon A heavier electron An electron hole A quasiparticle describing lattice vibrations An impurity that causes losses

The diffusion length of the free electrons has to be greater than the thickness of the wafer, for the semiconductor to work and create a potential difference successfully. True False

The absorber layer is neutrally charged. Tue False

True or false: A slope in the quasi-fermi levels indicate that there is current travelling through our system. True, or False?

The thickness of the absorber layer should be : Bigger than the diffusion length of the charge carriers Smaller than the diffusion length of the charge carriers Exactly equal to the diffusion length of the charge carriers

Solar cell is in equilibrium when: The cell is illuminated. A current is caused to cell by external source The current is zero and the cell is not illuminated

True or false: When the diffusion length of an electron in a material is less than the thickness of the wafer the electron is in, the electron will always reach the depletion region. True, or False (they will in fact never reach the depletion region if this is the case)

What’s the order of magnitude of the ratio of holes-to-electrons and of electrons-to-holes in a p-type Si and n-type Si, respectively? 101 103 107 >1010

What’s the order of magnitude of depletion region as a function of the thickness of the wafer? 0.001% 0.1% 1% 10%

What causes the built-in voltage across a PN-junction? The n- and p-regions are oppositely charged Charge carriers diffusing across the junction and recombining It is only a correction factor used to model the threshold behavior of the junction

In depletion regions… No majority carriers can move through There are no ionized atoms An electric field is formed

What happens in the depletion region? Electrons drift into p-type material and holes to n-type material The opposite

When a p-n junction is formed, drift current of electrons will flow… From p-type to n-type From n-type to p-type

2.1 How do the electrons flow trough the external circuit? From n-side to the heavily doped p-side From the heavily doped p-side to n-side

What is the typical construction of a crystalline silicon solar cell? p-n-n n-p-n p+-p-n n+-n-p

Which is the correct structure and order of the components in typical semi conductor solar cell front contact – n-type Si – p-type Si – heavily doped p- type Si – back contact front contact – p-type Si – n-type Si –– heavily doped p- type Si – back contact front contact – p-type Si –– heavily doped p-type Si – n -type Si – back contact

Which of the following are losses that affect solar cell performance? Surface recombination Thermalization Phonon scattering Reflection Fermi ionization

The internal electric field in depletion region is created by Electrons Holes Ionized dopants

Is the open circuit voltage the maximum voltage that a solar cell can deliver? Yes No The answer depends on the light intensity

A forward bias decreases the potential difference across the p-n junction. True False

Which charge concentration increases when p-n junction is illuminated? The concentration of minority carriers The concentration of majority carriers The concentration of ions

Choose the correct alternative(s) For effective solar cell, the depletion region should be close to region where the excess minority carriers are photogenerated Doping concentration decreases the diffusion length of the minority carrier The difference between the quasi-Fermi levels relates to how efficiently light is converted to chemical energy All the above

In a PN solar cell, in which layer does the electron/hole separation occur? n-type Si (membrane) p-type Si (absorber) p++-type Si (membrane) In the junction of p- and n- type Si In the junction of p- and p++-type Si

What is the largest losses in a single junction typical crystalline silicon solar cell. Spectral mismatch Reflection and transmission Fundamental recombination Excess recombination Resistance

What is the typical conversion efficiency of commercial crystalline silicon solar panels? 10-12 % 12-17 % 17-18 % 18-20 % 20-22 %