flyer: co-diffusion for n-type solar cells · contact back junction (left) and bifacial solar cells...
TRANSCRIPT
F R A U N H O F E R I N S T I T U T E F O R S O l A R E N E R g Y S Y S T E m S I S E
Co-Diffusion for n-Type solar Cells
N-type solar cells offer the highest
conversion efficiencies due to the absence
of light induced degradation and the
lower sensitivity to common impurities
like iron. These advantages are expected
to strongly increase the market share
of n-type solar cells in the near future.
Large scale industrial production of n-type
solar cells requires cost effective process
solutions.
At the Fraunhofer Institute for Solar Energy
Systems ISE we develop process sequences
for n-type cells that considerably reduce the
number of process steps. A key technology
is the simultaneous diffusion of p and n
dopants by co-diffusion. Our expertise
covers the application and characterization
of a wide range of dopant sources as well
as process development for different cell
structures from prototyping to industrial
implementation.
Our services include the integration of new
dopant sources in existing processes. We also
provide cell half fabricates for evaluating
customer process lines. Our expertise and
excellent infrastructure enable us to trans-
form our customers‘ ideas and visions for
n-type solar cells into functioning processes.
Co-Diffusion Approach
With our co-diffusion approach we offer a
cost-effective method for simultaneously
generating p- and n-doped regions within
one single thermal process. The use of
conventional tube furnaces allows for high
throughput and easy integration in existing
production lines. Prototyping at our clean
room facilities (ETALab) ensures demon-
stration on a high efficiency level while
processing at the Photovoltaic Technology
Evaluation Center (PVTEC) enables a fast
and direct transfer of results into industrial
production.
1 High throughput diffusion furnace.
2 Bifacial solar cell (left: front side,
right: rear side).
3 Back contact back junction (BC-BJ)
solar cell.
Fraunhofer Institute for
Solar Energy Systems
Heidenhofstrasse 2
79110 Freiburg
Germany
Phone +49 761 4588-0
Fax +49 761 4588-9000
www.ise.fraunhofer.de
Silicon Photovoltaics –
Doping and Diffusion
Dr Andreas Wolf
Phone +49 761 4588-5580
sipv.doping @ise.fraunhofer.de
September 2014
1 3 2
Equipment and Processes
We offer co-diffusion processes using
combinations of
n POCl3- or BBr3 tube furnace diffusion
n inline diffusion
n phosphorus and boron ion implantation
n phosphorus and boron-doped layers
deposited by CVD
n printed dopant sources
Our flexible doping profiles are applicable
for a wide range of solar cell concepts. In-
line characterization allows for contactless
in-depth characterization of large batch
sizes. Possible wafer sizes are 125, 156,
and 210 mm edge length.
Research and Testing Facilities
The cleanroom facilities (ETALab), the
Photovoltaic Technology Evaluation Center
(PVTEC) and the PV Module Technology
Center (Module-TEC) at Fraunhofer ISE
are the ideal platforms for advanced
concepts and processing on a pilot line
scale. Our accredited characterization labs
CalLab PV Cells and CalLab PV Modules
enable high precision IV-measurements
while the reliability according to IEC 61215
is tested in our Testlab PV Modules.
Expertise and Services
n industrially relevant process sequences
for numerous n-type solar cell concepts:
- screen printed bifacial
- back contact back junction
- others like PERL and PERT
n optimization of diffusion processes
and dopant concentration profiles in
co-diffusion processes
n combination of diffusion and implant
anneal processes
n control and characterization of cross
doping effects and reproducibility
n detailed characterization of doped
regions regarding dopant concentration
profile, carrier recombination and
contact resistance including device
modeling
n high efficiency processes at the clean
room facilities
n solar cell fabrication under industrially
relevant conditions with batch sizes of
several thousand solar cells
n adjustment of doping processes to
different wafer materials and surface
conditions
n characterization of solar cells, also with
regard to module integration
n module integration at the PV Module
Technology Center (Module-TEC)
n detailed cost of ownership calculation
for individual process and full process
sequences
1 Scanning electron microscope cross section
image of a doped region formed by co-diffusion.
2 Structured doped layers for BC BJ solar cells.
1
4 Boron and phosphorus dopant concen-
tration profiles generated by co-diffusion
processes using different dopant sources.
3 Example for co-diffusion setup for back
contact back junction (left) and bifacial solar
cells (right)
N -TYPE WAFER 1 µm
BORO
N D
OPED
EmITTER
BORON DOPED CVD lAYER
PSG
n++-Si
n+-Si
BSG
p++-Si
POCl3 BSG
p++-Si
n+-Si
POCl3 SiOx
depth (nm)
500 1000
phosphorus
boron
carr
ier
conc
entr
atio
n (c
m-3)
1021
0
1020
1019
1018
1017
1500
2 200 µm
PSg/S iO x/BSg
BSg
S iO x