1. Multiple choise questions related to lecture PV2

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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.

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

10. 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

11. The absorber layer is neutrally charged.
Tue
False

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

13. 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

14. 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

15. 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)

16. 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

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

18. 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

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

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

21. 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

22. 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

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

24. 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

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

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

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

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

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

30. 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

31. 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

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

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