Transcript SLUNCE A ŽIVOT

Solar cell fabrication technology
Vítězslav Benda,
CTU Prague, Faculty of Electrical Engineering
Market share by solar cell technologies
At present, nearly 90% of solar cell production
is made from crystalline silicon
Preparing semicondutor silicon
C
CD
NaCl
SiO2
arc furnace
electrolysis
NaOH
silicon grinding
Cl2 - drying
H2 - purification
HCl - production
fluid-bed reactor, SiHCl3 - production
condensation
distillation
high purity distillation
polysilicon deposition with doping
condensation
polysilicon processing
SiCl4
Polycrystalline silicon fabrication
SiHCl3 + H2 → Si + 3HCl
Monocrystalline silicon fabrication
(Czochralski method)
- diameter up to 450 mm
- weight up to 300 kg
Single-crystal fabrication
polycrystalline silicon processing
FZ-pulling
CZ-pulling
single crystal rod shaping
slim-rod pulling
Wafer fabrication
crystalline silicon shaped rod
sawing
lapping
sawing
etching and cleaning
etch rounding
solar cell grade quality wafer
cleaning
polishing
microelectronics grade quality wafer
Multicrystalline rod fabrication
Wafer fabrication
isotropic etching (HF +
HNO3 + CH3COOH)
texturing by anisotropic
etching
~40% of material is lost
during crystalline rod
cutting (sawing)
Ribbon silicon (~ 300 µm thick polycrystalline silicon sheets)
EFG (Edge-defined Film-fed Growth)
method
The ribbons are prepared in a
form of a hollow octagonal tube
(5 m in length) with eight 100 –
125 mm wide faces.
Diffusion technology
PN junction is usually realised by phosphorous diffusion
into P-type basic material
x
N ( x , t )  N 0 erfc
Dt
 x2 
Q
N  x, t  
exp 

 4 Dt 
Dt
ND(xj;tdiff) = NA
  W 
D(T )  D0 exp

kT


The structure of a high efficient solar cell
(PERL) made from monkrystalline silicon
(efficiency 24%)
FZ starting material
microelectronics quality
wafers
photolihography
anisotropic etching
diffusion
AR coating
photolithography
contact deposition
very expensive
technology
To decrease the fabrication cost….
•CZ quality material
•Wire-cut wafers
•Chemical surface
processing (texturing)
- etching monocrystalline (1,0,0) Si
in KOH
- acid etching in the case of other
crystallographic orientation of Si
•To avoid expensive fabrication
techniques like photolithography
and vacuum deposition techniques
Standard mass production (c-Si cells)
• chemical surface texturing
• SiN(H) antireflection
surface coating and
passivation
• contact grid realised by the
screen print technique
Fabrication of c-Si solar cells
- etching of damaged layer
- texturing
- N-type (P) diffusion
- Si3N4 ARC
- Ag/Al print screen BS
- Ag print screen FS
- firing of contact pastes
- edge grinding
- measuring and sorting
c-Si wafer
Crystalline Si solar cells
(area up to 400 cm2)
mono-crystalline
  17%
multi-crystalline
  16%
PV module technology
solar
cell
PV module
rubber
sealing
hardened
glass
EVA
Module lifetime
> 20 years
Al frame
back covering
foil (tedlar)
solar cells
Alternative module constructions
- between two glass sheets
- sealing compound application
- laminate foil application
- hind side from non-transparent material
Thin film solar cell technology
A) Vacuum deposition
Filament evaporation
Electron-beam evaporation
Flash evaporation
Sputtering
TCO for „light trapping effect“
ZnO sputtered and
etched in HCl
ZnO prepared by CVD
(Chemical Vapour Deposition)
B) CVD (Chemical vapour deposition ) technique
CVD technology is the formation of a stable
compound on a heated substrate by the thermal
reaction or decomposition of gaseous compounds
• Reaction chamber
• Gas control section
• Timing and sequence control
• Heat source for substrates
• Effective handling.
Atmosphere CVD
Low pressure CVD (LPCVD)
LPCVD is used for
deposition of silicon nitride 3SiH4 + 3NH3 → Si3N4 + 12H2
deposition polysilicon layers SiH4 → Si + 2H2.
Plasma enhanced CVD
(PECVD)
RF electrode and
substrate create the
capacitor structure.
In this space the plasma
and incorporated
deposition of material on
substrate takes place
The deposition rate is higher than in the case
of LPCVD, but layer quality is lower
Hot wire chemical vapour deposition
(HWCVD)
This technique relies on the
catalytic decomposition of
SiH4 by metal.
A filament is a basic
component in this system.
The gas in presence of a
heated filament (the filament
material is W or Ta) is
decomposed in radicals that
diffuse to and are deposited on
the substrate
The deposited layer structure depends on the gas
composition and substrate temperature
dilution ratio
rH = ([H2] + [SiH4])/[SiH4].
rH < 30, amorphous silicon growth
rH > 45, crystalline layers are formed
Tandem solar cell – „micromorph“ (microcrystal + amorphous)
Differences between crystalline
Si cells and thin film cells
Crystalline Si
thin film
thickness
300 mm
0.3 až 3 mm
structure
n+-p(-p+)
p+-i-n+
Technology n+-diffusion into substrate plasmatic processes
Illumination
FS contact
BS contact
antireflection
from „n+- side“
„fingers and busbars“
„not important“
texturing
from „p+- side“
all-area TCO contact
back reflector
TCO light trapping effect
Thin film modules
The module area is limited by the reaction
chamber volume
Very expensive equipment
Module lifetime ≤ 10 years
Present market
development
100
Slope of Scale-Up: Half the Cost with 10 times more
Volume
Price per Unit
10
Crystalline
Si
1
2002
Thin Films
1
Implementation
2
Progr.
Technology Transfer
Funding
0,1
Mechanism
s as driver
0,01
10
High Eta,
Lowest Cost
3
Research & Dev
100
1000
10000
Cumulative Quantity Produced
100000
Manufacuring cost in EUR/Wp for different crystalline Si
manufacturing for production of 500 MWp per year
A silicon ribbon
B multicrystaline Si
C monocrystalline Si
Fabrication step
A
B
C
Ingot growing
0,37
0,37
0,73
Wafering
0,00
0,29
0,24
Solar cell fab.
0,15
0,15
0,19
Module fab.
0,43
0,40
0,37
Factory Cost
0,95
1,21
1,53
Concentrator systems
heatsink
cells
parabolic mirror
The Sun tracking is necessary
Reliability problems
• Environmental effect and aging results in a decrease of
efficiency
A target: increase module
– a decrease of glass transparency
lifetime > 30 years
– an increase of series resistance
– degradation of individual layers of the cell structure
900 kWh/m2
1800 kWh/m2