Shit 2 Flashcards
Learn shit 2
Whats 1eV?
1.609x10^-19J
Energy of a Photon?
E= (hc)/λ or E = hf as f = c/λ
Beer Lambert law?
A = εcl where A = -log(I/Io) Also where εc = α
Fresnel Equation? What is it used for?
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.
Fill factor equation?
Pmax (Max Power)/Isc (short circuit current) x Voc (Voltage open circuit)
Effeciency?
n = (FFxIscxVoc)/(Power in)
In other words Pmax/Pin
Incident Photon current efficiency?
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.
Whats a conductor? Give an example.
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.
What is a hole?
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.
What is an Insulator?
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.
What is a semiconductor?
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.
As temperature increases, what happens to the conductivity of a Conductor?
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.
As temperature increases, what happens to the conductivity of a Semi-Conductor?
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.
Thermal Energy Equation?
E = Boltzman Constant x Temperature
Whats the difference between intrinsic and Extrinsic Semi conductors?
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!