Chp 15: Light Management for PV

Question 1

Know and explain the different types of optical losses and their relation to the efficiency

Answer 1

Key optical losses which require light management are:

• Reflection
• Shading
• Poor Absorption

Question 2

What is the state-of-the-art light management in Si solar cells. How does it work with regard to

• Reducing light reflection

Answer 2

Strategies to overcome:

1. Anti reflection coatings
2. Microtextures which enforce multiple incidences on the surface
3. Nanotextures which induce a gradual matching of the refractive index

Question 3

What is the state-of-the-art light management in Si solar cells. How does it work with regard to

• Light trapping

Answer 3

1. Back reflector; double the path of light
2. Light scattering; increase light path by scattering angle

total internal reflection; alpha = asin(n_1/n_2)

Question 4

What is the state-of-the-art light management in Si solar cells. How does it work with regard to

• Avoiding shading and area losses

Answer 4

Shading losses - the challenge of designing metal contacts

• We essentially want to reduce the shine and make the solar panel black (a black body emitter)
• Using interdigitated back contact solar cells = black cells.
• Covergency effiency of SI solar 23.8%

Question 5

What is the conceptual difference between the state-of-the-art light
management in Si solar cells and nanophotonic light management
concepts

Answer 5

Crystalline silicone wafers are an expensive component of the SI solar cell; therefore, we want to go thinner.

However, conventional light management is not compatible with thin Si.

Therefore, need to go nano to achieve advanced light trapping for ultra-thin film technologies

Question 6

What is the critical dimension for nanophotonic structures

Answer 6

1 micrometer

Question 7

How does light management/optics of a solar cell increase with the concentration coefficient?

Answer 7

jsc = c.jsc

The concentrated short circuit current density increases with c