Development of 19% Efficient 243.4 cm2 Cast
Multicrystalline Si Solar Cells through Material
Quality Enhancement and Implementation of
Advanced Design Features
Saptharishi Ramanathan
•
Names of contributors: Ajeet Rohatgi, Saptharishi Ramanathan, Ian B. Cooper,
Brian Rounsaville, Jiun-Hong Lai, Arnab Das, Malka Kadish
•
Project No: 2011-GIT-2 (Start : May 2011)
•
Project length: 2 year project
•
Report Type: Semi-Annual Report
Mentor: Ning Duanmu ( GT Solar)
Project Deliverables
Investigate lifetime limiting defects in cast Si as a function
of grain size, advanced crystal growth, and cell processing
using photoluminescence, IQE, LBIC, dark IV, etc.
Expected
Completion
Date
End of year 1
Develop junction formation techniques, rear dielectric passivation,
and selective emitter methods best suited for high efficiency castmono/mc-Si.
End of year 1
Produce monocast solar cells with advanced features like selective
emitter, Boron back surface field, and local Al back surface field.
End of year 2
Demonstrate ≥19% large area cast-mono and mc-Si solar cell
efficiencies using optimized gettering, passivation, and advance
features.
End of year 2
2
Recap
Gettering effect on various types of mc-Si
substrates
250
mc-Si
200
200
Large grain mc-Si
Lifetime (µs)
Cast Mono
150
153.5
Cz
133
133
124
115
100
50
50
21
0
58
46
31
2
As Grown
POCl3
POCL3, SiNx, Fire
4
Bulk lifetime progress with solar cell processing
steps of different regions of mc-Si ingots
21
mc-Si
Advanced mc-Si
Efficiency (%)
20
19
18
17
Baseline Cell: 17.2%
16
Improved BSRV/BSR: 20.4%
15
0
50
100
150
200
Bulk Lifetime (μs)
250
300
350
5
Study of advanced mc-Si ingot varieties
• Advanced mc-Si material of different varieties were
developed
• After initial experiments, “Ingot 1” material was found to
be of a very high quality
• This material was useful to provide a proof of concept on
good performance of full BSF and high efficiency cell
designs
• After subsequent experiments, “Ingot 3” material was
developed
• Ingot 3 was expected to provide a compromise between
manufacturability and performance
6
Comparison of Efficiency distribution on
advanced multicrystalline and Cz substrates
7
Examples of High Efficiency Advanced Design Cell
Structures fabricated on mc-Si substrates
• Renesola – 17.5% - 18.2% in production
• JA Solar - 18.2% in pilot production (156×156mm
200 m thick cells)
• Mitsubishi
• 19.3% on 156×156 mm 200 m thick cells
• Q cells
• Dielectric passivated PERC type cells
• ~19.7% world record efficiency on 243 cm2 cells
• Front contact : Screen printed seed layer + LIP
• Laser Fired Contacts (LFC) local rear contacts
8
Recent advancements in Quasi-mono
• Q – Cells – Q.antum technology
– 60 cell panels with 283 W rating
– “Functional nano layers and local contacts”
• Schott solar - 19.9% on quasi-mono confirmed by
Fraunhofer Cal Lab.
• JA Solar – “Maple” solar cells: 18.5% efficiency in
high volume production
– 60 cell Maple panels with >250 W rating (270-300 W
on website)
– Increased production of Maple cells to 480 MW
• Renesola – “Virtus” wafer capacity to increase to
1.8 GW
• Yingli solar also planning on using Quasi-mono
9
Current work
Cast mono ingot break down
Ingot A: Commercial
Ingot B: Prototype
Center Brick
Center Ingot
Top
Top-Middle
Side Ingot
BottomMiddle
Bottom
Corner Ingot
11
Prototype Ingot - center brick
Lifetime “slug” from prototype brick
13
Prototype – Center brick – Full BSF
14
Prototype – Center brick – Local BSF
14
Casting test
Cast mono – Ingot break down
Ingot A: Commercial
Center Ingot
Side Ingot
Corner Ingot
17
Near-seed region of ingot - Mosaic
18
Bottom Region of Ingot – Mosaic
19
Middle region of ingot - Mosaic
20
Top region of ingot - Mosaic
21
Vendor A – As-grown lifetimes
22
Vendor B – As-grown lifetimes
23
Average efficiency by region
Side
Center
Top
16%
(15.7% avg)
16.7%
(16.6% avg)
17.5%
(17.4% avg)
Middle
15.3%
(15.2 avg)
16.5%
(16.4% avg)
17.8%
(17.7% avg)
Bottom
17%
(16.9% avg)
17.4%
(17.2% avg)
18.2%
(18.1% avg)
15.9%
(15.7% avg)
15.8%
(15.8% avg)
16.8%
(16.7% avg)
Corner
Near
Seed
24
Vendor A – Center brick
25
Vendor A – Corner brick
26
Vendor A – Side brick
27
Vendor B – Efficiency distribution
28
Vendor – B – JSC distribution
29
Contact resistance trends
Near seed
Bottom
Middle
Top
30
Conclusions
• Achieved cell efficiency of >18 % on cast-mono from
3 different vendors
• Performed casting experiments to demonstrate
commercial viability of different cast mono ingots
• Performed lifetime measurements to chart the
response of various regions of the ingot to cell
processing
• Identified specific causes that limit cell performance
in cast mono wafers when compared to Cz
• Identified scope for future studies and
standardization of results
Acknowledgements
MEMC
GT Solar
REC
Dupont
Heraeus