1. Searching for Solar Breakthroughs Silicon & III-V Based PV
Breakout Session #2
Silicon & III-V Based PV
Colorado Rural Electric Association
7th Annual Energy Innovations Summit
Denver, Colorado
Dr. David Young
National Renewable Energy Laboratory
Golden, Colorado - USA
12 September, 2016

2. Globally, 47 GW of new photovoltaic panels were installed in 2015.
That’s like building 54 averaged-sized nuclear reactors in one year
~860 MW/reactor
15% capacity utilization for PV
77% capacity utilization for nuclear
> 90% of all PV
is crystalline silicon
Renewable energy world.com
PV Magazine, June 2016

3. Crystal Silicon Solar Module Production
metallurgical
grade Si
Sand
Add Carbon & Heat Energy
pure
SiHCl3 or
SiH4
Add
HCl + heat
Wire sawn wafers
Waste ~1/2
in sawing
Add Heat Energy
(1000 °C)
Add more heat energy (1500°C)
Si Boule
Poly-silicon
feedstock
Use 4X more silicon than needed for
Solar cells
Energy payback < 2 years
System payback < 7.5 years
$3.65/W to install in Colorado
½ the cost of a solar cell
is in the wafer.
3-9 GJ/m2
Renewable and Sustainable Energy Reviews
Volume 47, July 2015, Pages 133–141

4. Current Trends in Silicon Solar Cells to Decrease $/W
metallurgical
grade Si
Sand
pure
SiHCl3 or
SiH4
Gas-to-wafer (epitaxial growth)
- Crystal Solar (CA)
Wire sawn wafers
Continuous-pull boules
-GTAT (MT)
Si Boule
Direct-to-wafer technology
-1366 Tech. (New York)
Poly-silicon
feedstock
Multicrystalline wafers
Small grains – high lifetimes
Use 4X more than needed for
Solar cells
High efficiency solar cells
-SunPower (CA)
-SolarCity (New York)
-Suniva (GA)
-Panasonic (Japan)
- (China, Korea, Tiawan)
Bifacial module mounting
to collect sunlight from both sides
of the module.

5. Standard Al back contact silicon solar cell
Leaky bucket analogy
(fewer leaks = higher voltage)
Dominates market
Efficiency: 15 – 17%
Multicrystalline wafer
< $0.40/W cost
Very poor back contact
“Passivated” Emitter and Rear Contact (PERC) solar cell
Gaining market share
Efficiency: 18-20%
More processing steps
Better front contacts
Better back contact

6. Heterojunction Solar Cell
Reflection loss
SiO2, a-Si, PolySi, MoOx, LiFx
High efficiency 22-25%
Few, but precise process steps
Bifacial modules
Small market share
Solar City (Silevo) building new Giga watt factory in NY
Interdigitated back contacted (IBC) Solar cell
No front contacts
Highest Efficiency
cells 25.6% (max ~26.4%)
modules 24.1%
Many process steps
SunPower product
Using these techniques five companies/institutes have broken the 25% efficiency mark.

7. Crystal Solar (CA)
Direct Gas to Wafer Technology
Epitaxial Si layer
for solar cells
24% cells
50% less silicon
50% less capital costs
Much less energy/wafer
Wafers grown with junction preformed
Porous liftoff layer
Recycled parent wafer
1366 Technologies (NY)
Direct wafer process
Avoids kerf loss
less energy to form
Wafers
19.1% cells
New Factory in NY
Hanwha Q-cells to purchase 700 MW of
wafers.
Directly form wafers
from molten c-Si

8. Bifacial Modules
Cells and modules built to allow light to enter from the front and back sides
Published field tests have indicated that a 10 – 40% increase in power
output is achievable.

9. Thin-Film GaAs Alta Devices (CA) 28.6% record cell
25% eff, flexible cells ~$100/W
MOCVD growth process
NREL is researching a lower-cost
route to the same product.
25% eff, flexible cells
Low-cost precursors
High deposition rates
In-line processing
100 x decrease in $/W