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Flashcards in Shit 2 Deck (23)
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1
Q

Whats 1eV?

A

1.609x10^-19J

2
Q

Energy of a Photon?

A

E= (hc)/λ or E = hf as f = c/λ

3
Q

Beer Lambert law?

A

A = εcl where A = -log(I/Io) Also where εc = α

4
Q

Fresnel Equation? What is it used for?

A

R = ((no - nx)/(no + nx))^2
This equation allows us to calculate how much light is reflected from a surface due to scattering. We can use anti reflective coatings on our cells to prevent this. The fresnel equation will have to be used twice in order to get the proper percentage.

5
Q

Fill factor equation?

A

Pmax (Max Power)/Isc (short circuit current) x Voc (Voltage open circuit)

6
Q

Effeciency?

A

n = (FFxIscxVoc)/(Power in)

In other words Pmax/Pin

7
Q

Incident Photon current efficiency?

A

IPCE = (e- collected)/(Incident Photons)

If you are given current, all you need to do is divide current by elementary charge 1.609 x 10^-19 and you get the amount of electrons.

8
Q

Whats a conductor? Give an example.

A

Most metals are examples of conductors. Conductors metals which have their Fermi Level within the Valence band of those atoms. (The highest occupied Molecular orbital HOMO). This means that the LUMO (the lowest un occupied molecular orbital) Overlaps the valence band (the HOMO), therefore it takes very little energy to promote an electron into the LUMO. This leaves behind a hole, but is different to hole of that in a semi conductor.

9
Q

What is a hole?

A

A hole is what is left behind after an electron has been promoted from the HOMO to the LUMO. This allows adjacent electrons to fill that hole causing electrons to move. A flow or movement of electrons is described as current.

10
Q

What is an Insulator?

A

An insulator is a material which has a very big band gap. This means that the Fermi level is also very high. Therefore it takes extremely high amounts of energy to promote an electron from the HOMO to the LUMO and therefore we say it is not a conductor. Therefore an insulator.

11
Q

What is a semiconductor?

A

A semi-conductor is a material with a low band gap but has a fermi level inbetween the valence band and conductance band. The fact that we have a low band gap means that we can use thermal energy to promote an electron from the HOMO (valence band) to the LUMO (conductance band) causing a hole to form, causing there to be current.

12
Q

As temperature increases, what happens to the conductivity of a Conductor?

A

Conductivity decreases. Why? As temperature increase the kinetic energy of the molecules increases causing more and more collisions. This causes interactions with the holes formed by the promoted electrons which causes a decreased flow of electrons reducing conductivity.

13
Q

As temperature increases, what happens to the conductivity of a Semi-Conductor?

A

Conductivity Increases. Why? More electrons are promoted into the conductance band leaving behind more subsequent holes. These holes are not entirely the reason for the increased conductivity. The fact that the electrons have jump into what is now a partially filled conductance band, they are free to move, therefore form a current, causing conductivity to increase.

14
Q

Thermal Energy Equation?

A

E = Boltzman Constant x Temperature

15
Q

Whats the difference between intrinsic and Extrinsic Semi conductors?

A

Intrinsics have no impurities and the number of electrons = the number of holes. Extrinsics have impurities known as dopants, and the number of electrons doesn’t = the number of holes. Dopants increases conductivity greatly!

16
Q

What types of doping are there?

A

N-type (Negative type) in which you add a foreign atom with a higher number of Valence electrons than your semi conductor, into it’s atomic network. P-type (Positive type) In which you add a foreign atom with fewer electrons in its valence shell than your semi conductors into its atomic network.

17
Q

How does N-type doping work?

A

N-type doping works by the foreign atom providing more electrons to the host semi conductor. This forms a Narrow donor band close to the conductance band in which it can supply electrons to the conductance band. Thus causing increased conductivity. It shifts the fermi level away from the center and towards the conductance band.

18
Q

How does P-type doping work?

A

P type doping works by the foreign atom with less valence electrons than the host forming an electron accepting band close to the valence band of the semi conductor. This means electrons can be accepted by the acceptor band leading to the formation of holes, increasing conductivity. It cause the fermi level to shift away from the center point and down towards the valence band.

19
Q

What Happens when an N-type host and a P-type host combine?

A

When an N-type and a P-type host are adjacent to one another, their fermi levels begin to equilibriate. How? The holes of the P-type dopant are attracted to the electrons of the N-type dopant, and vice versa. They come to a point where they equilibriate and therefore the fermi levels equilibriate. This also causes a charge seperation barrier in which an electric field is generated. This electric field can be manipulated in many ways, as it only allows for the transfer of current in one direction if the charge speration barrier is disturbed.

20
Q

What happens when a photon strikes a P-N Junction?

A

When a photon of light hits an P-N junction, it excites one of the electrons leaving behind a hole. The electron stays on the side of the electrons as the electric field produced earlier repels this movement. However the holes formed are attracted to the negative region of the electric field and this move toward it. If connected to a circuit, the holes and electrons will want to recombine, and therfore do so by travelling through the wire. This is how we can get these doped semi conductors to do work.

21
Q

Draw a diagram of a Dye Sensitized Solar Cell. Explain the steps.

A
Step 1: Photon Absorption
Step 2: Electron Injection
Step 3: Electron Transfer
Step 4: I3- + 2e-  3I-
Step 5: 3I- Gives is oxidised and donates its electrons back to the HOMO of the Dye.
22
Q

Describe the 5 steps of an OPV Draw a diagram!

A
Step 1: Photon Absorption
Step 2: Exciton diffusion toward Acceptor-Donor Interface
Step 3: Charge Seperation 
Step 4: Charge Transfer
Step 5: Charge Recombination
23
Q

Intercalation definition?

A

intercalation is the reversible insertion of a molecule (or ion) into materials with layered structures