Solar - PV Junctions

Question 1

How is voltage difference allowed in PV?

Answer 1

Breaking of the symmetry in the crystal structure.

Question 2

Doping

Answer 2

Introduces impurities to generate PV junctions…

Question 3

Types of Doping

Answer 3

Substituinal Impurities
Interstital Impurities

Question 4

What are n and p-type doping?

Answer 4

Introduction of column 3 and group 5 elements into the silicon structure.

Question 5

N-Type Doping

Answer 5

This is the addition of say phosphorous or arsenic, with one extra electron in their shell not participating in binding.

Question 6

P Type Doping

Answer 6

This refers to introudction of elements with one less electron

Question 7

N Type Doping features…

Answer 7

Little energy required to boost into conduction band, electron being weakly obund to nucleus

Question 8

Introducing elements with one less electrno…

Answer 8

Opposite effect on fermi level, not being sufficient bonding to four adjacent atoms

Question 9

Analogy of P-Type Doping

Answer 9

One of the neighbouring atoms thought of as having a hole of which valence band electrons can be easily excited

Question 10

How is asymmetry generated in a crystal lattice?

Answer 10

Combining p and n type doping where electrons move readily between fermi level and conducting/valence bands

Question 11

P-Junction

Answer 11

This is where the P-Type and N-type doping are next to each other.

Question 12

When does the diffusion current form?

Answer 12

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

Question 13

When are depletion regions formed?

Answer 13

Where density of majority carriers is small having opposite net charges of their original.

Question 14

Boltzmann Factor

Answer 14

This indicates competition between the hcarging energy and the thermal energy.

Question 15

What causes the boltmann factor?

Answer 15

Random thermal motion from n type to p type and vice versa…

Question 16

Mechanism of ejection of electrions from valence to conduction bands….

Answer 16

Electromagnetic radiation illumination

Question 17

Photodiode

Answer 17

A semi-conductor-based light sensitive element, generating currents proportional to illumination of the PN junctions

Question 18

If rceominbaiton is not so fast…

Answer 18

Electromagnetic radiation increases mobile electron amount in P-region, finding way to interface region, pushed into r region

Question 19

How does PN junction act as a photodiode?

Answer 19

Holes moving from n to p region.

Question 20

Why in band gap ecitation is Egap provided to external circuitnot exactly E gap?

Answer 20

Limits to efficienc based on voltage-current characterisitcs of photodiodes and recmobination

Question 21

Shockley-Queisser Limit

Answer 21

THe maximum light to electric power conversion efficiency of a single junction solar cell for a given illumination spectrum

Question 22

Open Circuit Voltage

Answer 22

This is the maximum voltage available from a solar cell.

Question 23

Short Circuit Current

Answer 23

This is the current through the solar cell when voltage across the solar cell is zero.

Question 24

How can OCV be described…

Answer 24

Potential shift needed to allign fermi levels of the n and p type regions.