Silicon based Solar Cell Technologies: Trends &...
Transcript of Silicon based Solar Cell Technologies: Trends &...
Dr. Sushil Kumar
Principal Scientist CSIR-National Physical Laboratory
New Delhi Email: [email protected]
2nd Annual Conference-Expo-Awards“Roadmap for Innovations in Solar Energy” - RISE 2017, 20-21 July 2017, Hotel Taj, New Delhi
Silicon based Solar Cell Technologies: Trends & Challenges
Outline
Various solar cell materials &
technologies
c-Si solar cell technology, its advantage &
limitations
Improved silicon cell device structures
Amorphous silicon solar cell: limitations &
away to HIT cell
Apex level solar cell testing & validation at
CSIR-NPL
Conclusions
Choice of Solar Cell Materials
Three Generations of Solar Cells
• 1st: Wafer based:
– Monocrystalline silicon 25%
– Polycrystalline silicon 20%
– Multi-junction cell (different band-gap materials) 40%
• 2nd : Thin Films:
– Amorphous thin film silicon 13%
– CdTe (Cadmium Telluride) 17%
– CIGS (Copper Indium Gallium Selenium) 20%
• 3rd : Low Cost and high Efficient:
– DSSC (Dye-sensitized solar cells)
– QDSSC (Quantum Dot-sensitized solar cells)
– OPV (Organic photovoltics)
– QDs-Polymer Hybrid solar cells
– Perovskite Solar Cells
Efficiency
Various Solar Cells Efficiency
Prog. Photovolt Res. & Appl, 25 (2017)
Types of cell junction
N-type
P-type
Eg: c-Si cell
N-type
P-type
Eg: CdTe, CIGS cell
Cell 1, Eg1
Cell 2, Eg2
Cell 3, Eg3
Eg1 > Eg2 > Eg3
N-type
P-type
Intrinsic, i, layer
Eg: a-Si:H cells
Homo-junction
Hetro-junction
P-i-N junction
Multi-junction
Junction is required to facilitate charge separation for PV operation
Eg: GaAs, a-Si cells
Band gap Efficiency of multi-junction cell
Appropedia, 2012
Triple-junction cells
Appl. Phys. Lett. 90, 183516 (2007) Emcore Corporation, May (2006)
1.7-1.9 eV
1.3-1.4 eV
0.67 eV
The cells are in series;
current is passed through
device
The current is limited by
the layers that produces
the least current.
The voltages of the cells
add
The higher band gap
must see the light first.
Multi-junction solar cells
Low-end tandems
Turning poor solar cells into average ones !
Multilayer amorphous silicon
-Different bandgaps via process control or a-SiGe alloy
• The semiconductor junctions can be:
– Single Junction p-i-n
• a-Si
• µc-Si
– Tandem Junction p-i-n/p-i-n
• a-Si/a-Si, a-Si/a-SiGe, a-Si/ µc-Si
– Triple Junction p-i-n/p-i-n/p-in
• a-Si/a-SiGe/a-SiGe
• a-Si/ a-SiGe/ µc-Si
• nc-Si/a-Si:H/ µc-Si
Efficiency: 10-11%
Efficiency: 12-14%
Limitation: a-Si:H Light-induced degradation & Low efficiency
Roll-to-Roll Process for Thin Film Silicon Solar Cell
Roll-to-Roll a-Si deposition machine (UNI-SOLAR)
Production-sized cells
Cross-section of the triple-junction a-Si alloy solar cell
Efficiency Comparison of Technologies: Best Lab Cells vs. Best Lab Modules
9.13 %
9.08 %
8.84 %
8.85 %
7.78 %
Source: PV Report, Fraunhofer ISE, 12 July 2017
Will the 1st-generation c-Si
PV technology be replaced by
2nd- and 3rd-generation PV?
Annual PV Production by Technology
(Worldwide in GWp)
Source: PV Report, Fraunhofer ISE, 12 July 2017
Fact: c-Silicon Share of Production 93% in 2016
PV Production by Technology
Source: PV Report, Fraunhofer ISE, 12 July 2017
Current Efficiencies of Selected Commercial PV
Modules
Source: PV Report, Fraunhofer ISE, 12 July 2017
Crystalline silicon solar cells: Better than ever
Silicon-based photovoltaics dominate the market. A study now sets a new record efficiency for large-area crystalline silicon solar cells, placing the theoretical efficiency limits within reach
What is best efficiency possible in silicon solar cells
Shockley, Queisser (JAP 1961): Efficiency limit of solar cell made of one material = 33% (AM1.5)
Theoretical efficiency for
silicon = 29.4%
Best Silicon cell = 26%
88 % of theoretical efficiency
Different solar cell technologies strives to
maximize the efficiency
It requires
- Absorption of photon
- Separation of electron-
hole pair
- Collection of the charges
at electrodes
Three operations in different way
P-N Jn –separation force
Metal contact
Metal contact
The theoretical limit for a crystalline silicon solar cell is ~ 29%.
C. Battaglia, Energy Environ. Sci., 2016, 9, 1552--1576
Analysis of recombination losses of the exemplary
n+pp+ silicon solar cell
P-type -c-si wafer
Phosphorus diffusion
a-SiN:H
Al-doped
BSF (back surface filed)
Aluminum doping from the back contact into the silicon wafer is confined to the small openings in the rear passivation layer, minimizing recombination.
The dielectric passivation layer simultaneously improves the reflectivity of the aluminum back reflector.
Localized rear contact solar cell with dielectric rear surface passivation
Significant electronic and optical benefits
C. Battaglia, Energy Environ. Sci., 2016, 9, 1552--1576
Ways:
Restricting the aluminum alloyed p+ region to a small
fraction (about 1–5%) of the rear surface while
passivating the rest with an insulating material
High Efficiency Concept of c-Si cell: Ways & Approach
Three Approaches (also referred to with the acronyms):
PERC (Passivated Emitter and Rear Cell)
PERL (Passivated Emitter, Rear Locally-doped)
PERT (Passivated Emitter, Rear Totally diffused)
Method: Laser ablation. 1130 local contact openings (in
industry typically as lines) are made in the insulator
PERL
PERC PERT
HIT Solar cell
Wafer based Crystalline
Silicon Silicon solar cell
Amorphous thin film
silicon Solar cell
Highest Conversion
Efficiency
Module Efficiency: 18-20%
Cost reduction is main
overall challenge
Low cost Potential
Module Efficiency: 6-9%
Efficiency enhancement is
major challenge
Hybrid Technology HIT Solar cell
HIT: Hetrojunction with intrinsic thin layer
Present status of efficiency of HIT solar cell
(INTERNATIONAL STATUS)
Institute/ Company Year Efficiency (%) Area (cm2)
Kaneka Corp., Japan 2016 26.3 180.0
Panasonic, Japan 2014 25.6 143.8
Sanyo, Japan 2014 24.7 124.2
AIST, Japan 2013 18.2 0.2
RRS, Switzerland 2011 21.9 4
EPFL, Switzerland 2011 21.8 4.5
HZB, Germany 2008 19.8 1
NREL, USA 2009 18.2 0.9
LG, Korea 2010 19.1 1
Delft, Netherlands 2011 15.8 2
CEA, INES, France 2010 15.7 25
BHEL, India (at R&D level on industrial wafer): 18%
HIT – “Hetrojunction with intrinsic thin layer”
Structure of HIT solar cell
Intrinsic a-Si:H used for c-Si surface passivation: dangling bond passivation (surface recombination becomes crucial when device thickness decreases)
Doped a-Si:H for diode
creation (front end) and BSF (back contact)
TCO: Optimized optical
performances
Advantages of HIT solar cell over C-Si solar cell
Non regular Grid area = Defective area = relatively high surface recombination
Clean surface area = Suppressed surface recombination
http://www.posharp.com/hit-240hde4-solar-panel-from-sanyoelectric_p2075938320d.aspx
Processing Temperature ~900 0C Processing Temperature < 200 0C
Temperature coefficient of HIT solar module
Higher than standard
conditions temperatures
can actually mean
losses in maximum
output power
c-Si solar module:
-0.5% / degree Celsius
Power loss: 1% for
every 2°C increase
Simulation & Fabrication of HIT Solar Cells
Float zone c-Si (1-2 Ω cm, > 2 µsec, 200 µ thick, <100> orientation) wafers.
Standard RCA cleaning. Deposition of pure & doped a-
Si:H layers – PECVD (For n - PH3 and for p - B2H6).
TCO (AZO) deposition – Sputtering.
Contact formation – E-beam evaporation of Ag/Al.
Front grid –Screen printing/Inkjet printing/Photographic lift-off process
Market Share for different cell technologies
ITRPV 2017
Perovskite/silicon-heterojunction tandem solar cells
Journal of Optics 18 (2016)
Projected Efficiency 30% , however, stability of
Perovskite remain a challenge
Why validation needed for solar cell efficiency ?
“Most of the measurement
errors a researcher would
make would tend to make
the efficiency higher, not
lower”- Keith Emery,
NREL
An error in solar cell/module
efficiency leads to error in the
over all assessment of related
product & system.
The largest source of error in estimating the efficiency of a solar cell is arguably the correct
identification of its active area.
Effect of active area on efficiency of organic solar cells
(Measurement performed at CSIR-NPL)
Cell Area: 2 mm x 3 mm = 6.0 mm2
(Actual Area: 1.970 mm x 2.968 mm = 5.84696 mm2
Dimension accuracy in NPL @0.16 µm (in 1mm)
Pin : 1000 W/m2
(< 25% spectral mismatch)
Eff. measured at temp. 25 °C
NPL - NMI
(Apex Calibration)
NPL has expertise in calibration of the parameters
needed for validation of the solar cell efficiency
Optical Irradiance
Current
Voltage
Temperature
Dimension (Active Area)
Parameters Capabilities in Measurement Uncertainty
Spectral
irradiance
Wavelength: 350 - 2500 nm
(0.06 – 0.026 nm)
DC Voltage 1V (± 1µV), 1 mV (± 1µV), 1µV (± 0.1 µV)
DC Current 1mA (± 5nA ), 1µA (± 7pA),
1nA (± 0.1pA),1 pA (±0.01pA)
Temperature ±0.17 x10-3 °C at TPW (0.01 °C)
Dimension 1.0 mm (± 0.16 µm)
Validation of solar cell efficiency at CSIR-NPL
• Primary Standard Facility for Solar Cell
Calibration is under development at NPL
…….Recently MNRE has sponsored a Project
Measurement Traceability Pyramid
Efficiency Validation for organic solar cells
Secondary Standard Facility
Conclusions
c-Si solar cell is dominant technology, will remain for long….
Close Competition between PERC & HIT solar cells technology, perhaps HIT may make it winner in long run…..
Emerging & newer Thin-film solar cell materials for solar cells (OPV, DSSC, Perovskite, tandem…) present interesting advantages & showing high potential, however, its promising future for commercialization depends on its arrest of environmental instability