yale university photovoltaic properties of a revolutionary new solar cell drew mazurek advisor:...
TRANSCRIPT
yale university
Photovoltaic Properties of a Revolutionary New Solar Cell
Drew Mazurek Advisor: Jerry Woodall
April 30, 2002
solar cells in real life
• Cost-effective way to provide power to remote areas
solar cells in real life
• Cost-effective way to provide power to remote areas
• Environmentally-friendly renewable energy source
solar cells in real life
• Cost-effective way to provide power to remote areas
• Environmentally-friendly renewable energy source
• Power source for outer space applications
how solar cells work
The simple idea: photons in, current and voltage out
how solar cells work
A closer look: photons above the semiconductor’s band gap energy generate hole/electron pairs…
pn-junction
p
n
- holes
- electrons
h > Eg
how solar cells work
which then diffuse across the cell’s concentration gradients
pn-junction
p
n
- holes
- electrons
how solar cells work
Some holes and electrons recombine before they can reach the other side of the junction. In good cells,
however, there is very little recombination.
pn-junction
p
n
- holes
- electrons
how solar cells work
Most holes and electrons make it to the other side, resulting in a net charge increase on each side. This net charge increase is
realized outside the cell as current and voltage, or power.
pn-junction
p
n
- holes
- electrons
solar cells in space
To go into space, solar cells must be
• efficient – want to produce as much power as possible
• lightweight – launching satellites into space costs $5,000 per pound
Additionally, we’d like them to be
• inexpensive to manufacture – $$$
• radiation-hard – Van Allen Belt ideal place for satellites, but high radiation environment
solar cells at yale
Strong electric field (~1,000-10,000 V/cm)
n++ n p
Indium Phosphide drift-based design
surface
solar cells at yale
n++ n p
h > Eg
Indium Phosphide drift-based design
Strong electric field (~1,000-10,000 V/cm)
surface
Strong electric field (~1,000-10,000 V/cm)
solar cells at yale
n++ n p
Indium Phosphide drift-based design
surface
solar cells at yale
• motion of carriers due to electric field
• not as susceptible to material defects
• motion of carriers due to concentration gradient
• material defects shorten carrier lifetime, causing more recombination
Diffusion (theirs)
Drift (ours)
vs.
solar cells at yale
Strong electric field… so what?
• holes are immediately swept into the junction, producing power
• fewer hole/electron pairs are lost due to recombination – no time to recombine!
n++ n p
solar cells at yale
Strong electric field… so what?
• radiation damage decreases carrier lifetimes. Carriers swept by drift (electric) fields, however, aren’t affected as much.
n++ n p
solar cells at yale
Why Indium Phosphide?
• very high ideal efficiency: ~37% at concentration of 1,000 suns
solar cells at yale
Why Indium Phosphide?
• very high ideal efficiency: ~37% at concentration of 1,000 suns
• absorbs most light at small thicknesses – lightweight! 0
20
40
60
80
100
0.01 0.1 1 10 100 1000
Thickness (μm)
Abs
orbe
d P
ower
(%)
Si GaAs InP
solar cells at yale
Why Indium Phosphide?
• very high quantum efficiency across all wavelengths of visible light and UV – highly efficient and it makes good use of almost the entire spectrum 0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
100 200 300 400 500 600 700 800 900 1000
Wavelength (nm)
Inte
rnal
Qua
ntum
Eff
icie
ncy
1 µm InP (10 Å dead region)1 µm GaAs (100 Å dead region)1 µm Si (10 Å dead region)10 µm Si (5 Å dead region)
solar cells at yale
Yale’s InP solar cells are ideal for outer space applications:
• lightweight
• radiation-hard
• highly efficient
• low cost (~$1/cm2 vs. $10/cm2 for current high-efficiency solar cells)
summary
• Solar cells are simply pn-junctions in which hole/electron pairs are created from photons.
• The holes/electrons diffuse into the junction, and are immediately swept to the other side.
• The net charge gain is seen outside the cell as current and voltage, or power.
summary
• At Yale, we have designed and perfected the first ever drift-dominated solar cell.
• By collecting carriers with an electric field, we are able to create solar cells that are robust in the strong radiation of outer space.
• Additionally, our cells are lightweight and inexpensive.
acknowledgements
Many thanks to:
Professor Jerry Woodall
Professor Janet Pan
Yanning Sun