DuPont provides materials to enable higher efficiency solar cells through advanced technologies like interdigitated back contact, multi-wire, and n-type bi-facial cells. The presentation discusses DuPont products that can reduce optical and recombination losses to increase cell efficiency above 20%, such as fine line printing pastes and local back surface field pastes. It also reviews DuPont's roadmap to develop new materials to enable further efficiency increases through technologies like interdigitated back contact and multi-wire cells, with a goal of achieving 22% efficiency by 2015.

1. DuPont™ Solamet® Enable Next Generation High Efficiency Solar Cells
Dr. Alex Wu
Technology Manager, Taiwan
DuPont Microcircuit Materials
Aug. 16, 2013

2. © E. I. DuPont 2013
Efficiency (%)
Year
Conventional Cells
Solamet® PV14x Products
High Efficiency Cells
Solamet® PV15x, 16x
High Efficiency
LDE Cells
Solamet® PV17x, 18x
New LBSF
(LDE) Architectures
Solamet® PV36x
N-type Cell Bi-facial: PV3Nx
IBC: Pv197
Back Contact
MWT : Solamet® PV70x
Cell Efficiency Evolution
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Broad Capabilities Under One Roof
Design, fabrication, and characterization of advanced cell and module architectures
DuPont invest to support long-term industry growth.
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What’s the Main loss of Crystalline Si PV? Loss in Currents
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•Jmax: Theoretical maximum for a certain wafer thickness
•Jgen: Generated photo-current in actual device
1.Optical loss= Jmax- Jgen
2.Recombination & Resistive losses = Jmpp-Jgen

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Eff (%) 18.7 19 20 19.7 23
Voc (mV) 633 643 651 648 699
Cell Structure and Efficiency Evolution
N-ty pe IBC
N-ty pe Bi-facial
P-type PERC
P-ty pe LDE
P-ty pe STD
N-type IBC
N-type Bi-facial
P-type PERC
P-type LDE
P-ty pe STD
44
43
42
41
40
39
38
37
36
35
Current Density (mA/cm2)
ΔJ optical
ΔJ front
ΔJ Auger, base
ΔJ SRH, base
ΔJ rear
J mpp
Jmax
High-efficiency Silicon Solar Cells
Stefan Glunz
Fraunhofer Institute for Solar Energy Systems ISE
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Achieving higher solar cell efficiency with advanced
materials and technology
Fine line and MWT
Local Back Surface Field
N-type bi-facial
Interdigitated Back Contact
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Reduce the Optical Loss: Fine Line Print
Squeegee side
Wafer side
44 um
40 um
46 um
46 um
Fine Line Print

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Reduce the Optical Loss: MWT and Solamet ® PV70x
reference
PV70x
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Options 1:
Options 2:
MWT Module Assembly Options
•PCB as backsheet foil and ECA to connect
•High cost
•Cu foil and patterning process
•ECA
•Tab-string (manually or automated)
•Bowing and yield loss
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Reduce Rear Side Recombination: LBSF (PERC)
p-type Si
p+
Al paste PV36x
SiO2 or Al2O3
FS-Ag paste PV17x / PV18x
SiNx
i-PERC major advantage
- Minimized surface recombination velocity (SRV) - Increased internal reflectivity - Higher Voc, Jsc, and cell efficiency (up to 1%)
Other advantages
- Minor change in the cell/module production - Necessary for thin wafers (<150um)
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Surface Recombination Velocity and Types of Passivation
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+++++++++++++
P+
Induced n-type layer
+++++++++++
- - - - - - - -
P+
Al2O3 or SiO2 layer
Rear Shunting Issue and iPERC Solution
Direct Al L-BSF firing with SiNx passivation
iPERC
p type
p+ type
n type
n+ type
SiNx
SiO2 or Al2O3
Metal Positive charges in SiNx induce n-type layer at the rear interface. Direct metal contact to both p-type local BSF and induced n-type layer creates shunted junction → no BSF effect. Negative charge in the Al2O3 or SiO2 layer, together with the increased distance of the SiNx layer from the surface, prevent formation of induced n-type layer.
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Internal Reflection and Quantum Efficiency
Light absorbed Reflected light will generate
additional current
Standard Cell Local BSF Cell
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DuPont™ Solamet® PV36x for Local BSF
Strong adhesion to passivation and reliable module performance
Innovation in glass and Al powder technology for better contact
Reference
PV36x
Al
Si
Al
Si
PV36x
Reference
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406 nm
655 nm
875 nm
975 nm
PV505
PV56S
LBIC Test
•PV56S shows less passivation damage than PV505 (Width: Busbar=1.8 mm, Tabbing= 6 mm)
Solamet® PV56S for PERC BS Tabbing
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LID Issue for LBSF on Multi?
27th European Photovoltaic Solar Energy Conference and Exhibition Light Induced Degradation of Rear Passicvated mc-Si Solar Cells K. Ramspeck, S. Zimmermann, H. Nagel, A. Metz, Y. Gassenbauer, B. Birkmann, A. Seidl
mc-PERC
mc-BSF
mono-PERC
mono-BSF

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p+-Si (B-doped emitter)
n-Si (base)
n+-Si (P-doped BSF)
n+-Si (P-doped FSF)
n-Si (base)
p+-Si (B or Al-doped emitter)
Rear emitter N-cell
Rear p-contact (Ag/Al or Al)
Front p-contact (Ag/Al)
Rear n-contact (Ag)
Front n-contact (Ag)
Multiple options
•Front emitter or rear emitter
•Textured or planar rear
•SiO2/SiNx or Al2O3/SiNx passivation
•(BBr3, BCl3)/POCl3 diffusion, ion implantation, or other
•Lightly-doped emitter (LDE) and LD-BSF(FSF)
N-type Bi-facial
Front emitter N-cell

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DuPont™ Solamet® PV3N1: for N-type Bi-facial Cell
PV17x/PV18x
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IBC (Interdigitated Back Contact)

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DuPont™ Solamet® PV197: for IBC
Current paste system for IBC Electrode for n+ : Ag paste Electrode for p+ : Al or Ag/Al paste Firing temp. : >750degC
DuPont paste for IBC
IBC paste system
Electrode for n+ : Electrode for p+ :
Firing temp. : 550-600degC
Minimum damage to BS passivation.
Minimum thermal damage to Si.
Less wafer bowing. Good solder process compatibility.
p+
p+
p+
n+
n+
n+
One paste system
How to minimize wafer bowing ? How to make tabbing by solder ribbon ?
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New Architectures
IBC
MWT
N-type
Back
Rear Tabbing
Al Systems
Front
Single Print high adhesion
2010
2011
2012
2013
2014
2015
2016
Solamet® Product Generation Road Map
Front side contact
Rear contact
Interconnect
Interconnect
Double Print PVD2A
Non-fire through Ag Contacts for Gen 1/2 LBSF structures
PV17X for HE/LDE
Low Cost Alternative metal interconnect
Local Back Surface Field Al PV36X (Laser Ablated)
IBC Metallizations
Metallizations for decoupled interconnect (Dual Print) PVxxx
Full Plane back surface field Al
PV16A
PV18X for LDE +
PV19X for LDE ++
Improved performance, driving down consumption, improved adhesion & fine line capability
PV1XX Pb free
Low cost tabbing interconnects PV51X and PV52X
Low cost high adhesion non-fire through interconnect tabbing Ag
MWT Via Gen 1 : PV701
MWT Via Gen 1 : PV7xx reduced shunting
N-type : p-contact PV3N1
N-type : p-contact PV3NX – higher conductivity, lower contact & low Voc loss
Front side metallizations based on alternative metals
Gen 2 Lower CoO LBSF structures
Improving yields, reduce linewidth, maximize adhesion
Multiple print
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•20% cell has been realized in production
•The path to 22% is clear but needs…
• More cooperation between cell and module
• Simple and cost effective technology
• Innovative and integrated material solution, i.e. DuPont DPVS
•DuPont will continue to lead and invest the technology to realize high efficiency with low CoO in both PV cell and module production
• We commit to achieve 22% in 2015 mcm.dupont.com
Summary
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