Objectives and Theory

Question 1

What are the 3 objectives of the experiment?

Answer 1

• Building circuit to investigate current - voltage characteristics
• Show effect of varying levels of light intensity on cell output
• Determine efficiency of solar cell

Question 2

Health and safety points?

Answer 2

• Avoid staring in direction of lamp for prolonged period
• Lamp shielding gets warm after a length of time
• Electrical shock

Question 3

What is a solar cell?

Answer 3

Any device that converts the energy in light into electrical energy through photovoltaics

Question 4

What is a module?

Answer 4

Solar cells that are electrically connected and encapsulated as a module

Question 5

Why do PV modules has a sheet of glass on the front (sun up) side with a resin barrier behind?

Answer 5

Allows light to pass while protecting semiconductor wafers from the elements

Question 6

What protects PV modules from the elements?

Answer 6

A sheet of glass on the front side with a resin barrier behind

Question 7

What were the first solar cells made from?

Answer 7

Single crystal silicon wafers

Question 8

Efficiency of first solar cells?

Answer 8

6%

Question 9

At the beginning, what was the only application for solar cells?

Answer 9

Space

Question 10

How have efficiency been increased and price lowered of single crystal silicon solar cells?

Answer 10

Crystalline silicon solar cell technology has improved dramatically

(today is the dominant solar cell technology)

Question 11

What are solar cells made from?

Answer 11

Silicon - a semiconductor

Question 12

Make flashcards on experiment questions

Answer 12

Not yet

Question 13

What is the photovoltaic effect?

Answer 13

Generation of voltage and electric current with exposure to light

Question 14

What was used to create the first photoelectric cell?

Answer 14

Selenium

Question 15

How did Einstein describe light?

Answer 15

As packets of energy behaving as particles

whose energy varied with wavelength of light

Question 16

How is a p-type semiconductor made?

Answer 16

Doped with trivalent impurity atoms

Question 17

How is an n-type semiconductor made?

Answer 17

Doped with pentavalent impurity atoms

Question 18

Another word for doped?

Answer 18

Impure

Question 19

How to make a pn junction?

Answer 19

Put p and n type crystals together

Question 20

What happens to fermi level at equilibrium in the pn junction?

Answer 20

It is the same throughout

Question 21

What happens when p and n regions are connected?

Answer 21

Electrons diffuse into the p region and holes into the n region

Question 22

Why do electrons diffuse in pn junctions?

Answer 22

Due to the difference in concentrations of electrons and holes

Question 23

Once electrons have diffused in the pn junction, what happens to the impurity atoms?

Answer 23

The impurity atoms become ionised and create a space charge-limited current region -

Question 24

Result of space charge limited current regions?

Answer 24

Growing electric field opposing diffusion and leads to equilibrium

(fermi level equalised)

Question 25

What does the diffusion potential depend on in the pn junction?

Answer 25

• the amount of doping

* original difference between Fermi energy levels of separate p and n regions

Question 26

Distance between V and C bands in Si at room temp?

Answer 26

1.1eV

Question 27

What is a solar cell (Ito pn junctions)?

Answer 27

A pn junction with large surface area and has electrodes at either sides of P and N type layers

Question 28

How to photons relate to pn junctions?

Answer 28

If a photon with enough energy incident on semiconductor, can create electron-hole pair

(under electric field these drift to opposite directions)

Question 29

Which directions do the electron-hole pair drift?

Answer 29

Electrons towards N type

Holes towards P type

Question 30

What happens when the two electrodes are connected to a circuit?

Answer 30

Electrons flow around through external load and recombine with the holes attracting them in the p type

Producing direct current

Question 31

What can the semiconductor component in the solar cell also be called?

Answer 31

A photodiode with large SA

Question 32

Why do photodiodes in solar cells have large SA?

Answer 32

Light can penetrate the pn transition through a thin n or p conducting layer and create electron hole pairs

Question 33

How are electron hole pairs separated?

Answer 33

By the intrinsic electric field in the barrier layer

and can migrate in the reverse direction into the doped region

Question 34

How is light generated current made in the pn junction?

Answer 34

Electrons travel from the n to p type layer