Solar - PV Junctions Flashcards
How is voltage difference allowed in PV?
Breaking of the symmetry in the crystal structure.
Doping
Introduces impurities to generate PV junctions…
Types of Doping
Substituinal Impurities
Interstital Impurities
What are n and p-type doping?
Introduction of column 3 and group 5 elements into the silicon structure.
N-Type Doping
This is the addition of say phosphorous or arsenic, with one extra electron in their shell not participating in binding.
P Type Doping
This refers to introudction of elements with one less electron
N Type Doping features…
Little energy required to boost into conduction band, electron being weakly obund to nucleus
Introducing elements with one less electrno…
Opposite effect on fermi level, not being sufficient bonding to four adjacent atoms
Analogy of P-Type Doping
One of the neighbouring atoms thought of as having a hole of which valence band electrons can be easily excited
How is asymmetry generated in a crystal lattice?
Combining p and n type doping where electrons move readily between fermi level and conducting/valence bands
P-Junction
This is where the P-Type and N-type doping are next to each other.
When does the diffusion current form?
When the negative charge carriers(electrnos) travel from n type through thermal motion into p-type, where holes positvie charge carriers travel into n junctions
When are depletion regions formed?
Where density of majority carriers is small having opposite net charges of their original.
Boltzmann Factor
This indicates competition between the hcarging energy and the thermal energy.
What causes the boltmann factor?
Random thermal motion from n type to p type and vice versa…
Mechanism of ejection of electrions from valence to conduction bands….
Electromagnetic radiation illumination
Photodiode
A semi-conductor-based light sensitive element, generating currents proportional to illumination of the PN junctions
If rceominbaiton is not so fast…
Electromagnetic radiation increases mobile electron amount in P-region, finding way to interface region, pushed into r region
How does PN junction act as a photodiode?
Holes moving from n to p region.
Why in band gap ecitation is Egap provided to external circuitnot exactly E gap?
Limits to efficienc based on voltage-current characterisitcs of photodiodes and recmobination
Shockley-Queisser Limit
THe maximum light to electric power conversion efficiency of a single junction solar cell for a given illumination spectrum
Open Circuit Voltage
This is the maximum voltage available from a solar cell.
Short Circuit Current
This is the current through the solar cell when voltage across the solar cell is zero.
How can OCV be described…
Potential shift needed to allign fermi levels of the n and p type regions.
