‘Advanced Materials Development for Printed Photovoltaic Devices’

Prof. Darren Bagnall : APAC Innovation Summit 2016

Conclusions • Silicon-wafer based solar technologies are set to dominate the

photovoltaic industry for the next 10 years (at least) • This might include 30% tandem-on-silicon devices

• Printing technologies have a key role in Si device technology • Printing may have increasing role in future Si cell technology - lithography for interdigitated back contact (IBC) devices - lithography for light-management - printing for module assembly? • The ‘holy-grail’ remains cells/modules based on a printed (painted or

sprayed) advanced materials • known materials probably not good enough • there are important niches (building-integrated, consumer

electronics)

Overview Aiming: to provide an overview of PV technology, consider the role and opportunity of printing within PV technology.

Contents:

• Introduction to the School of Photovoltaic and Renewable Energy Engineering at UNSW

• The PV industry – current trends

• Photovoltaic Technologies

• Printing in Si PV technology

• Printed PV – the ‘holy grail’

• OPV/DSSC/Perovskites?

• Concluding Remarks

The School of Photovoltaic and Renewable Energy Faculty of Engineering, UNSW

Head of School: Professor Darren Bagnall

Scientia Professors Martin Green, Stuart Wenham Professors Gavin Conibeer, Allen Barnett, Thorsten Trupke,

Evatt Hawkes 20 Associate Professors, Lecturers and Senior Lecturers

47 Fellows and Research staff 24 Professional an Technical staff

100 HDR Students 400 UG, PGCWK

School of Photovoltaic and Renewable Energy

• 1974 Martin Green established Photovoltaic research at UNSW Electrical Engineering

• 1985 20% silicon cell

• 1993 20% standard module

• 1999 – 2005 ARC Centre of Excellence

• 2006 School formed

• 2008 25% silicon cell

• 2011Move to Tyree Energy Technology Building

• 2014 Solar Industrial Research Facility opens

• 2014 40.4% 1-sun solar conversion record

• 2016 Records for CZTS, Quantum Dot, Large area and Perovskite solar cells.

History of SPREE

Commercial Photovoltaics (1G) High-efficiency Si devices Hydrogenation Plating and Contacts Metrology and Varience

Advanced Concepts

3G 2G (OPV, Perovskites, CZTZ) Photonics, Plasmonics Materials

Distributed Energy Systems and Policy Energy Efficiency Resource modelling Policy

Research Themes

Commercialised Technologies • Buried Contact Solar Cells • Pluto Modules • Semiconductor Finger Cells • Laser Doping

Hydrogenation • New charge state control

techniques for hydrogenation • Transforms multi and UMG

material into being like single crystal

Plating and contacting technologies • Copper plating • Laser processes for contact

formation and localized doping

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Commercial Silicon Photovoltaics

Photovoltaics and Solar Energy Industry Trends

The Cost of Solar Energy

International Energy Agency 2016

The Learning Curve

International Technology Roadmap for PV (ITRPV) 2015

Balance of Systems Costs

• Balance-of-Systems cost is now 3 or 4 times the module cost • This places a premium on efficiency (cheap 10% probably isn’t good enough to

replace ‘conventional’ modules) • Important niches includes: - integrated products (on roof tiles, glazing, steel roofs) and systems - consumer electronics

Photovoltaic Technologies

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(M.A. Green, Prog. Photovolt: Res. Appl. 2001; 9:123-135)

First Generation • Silicon wafer based solar sells

Second Generation • thin film silicon • CdTe/CdS • CIGS • DSSC • Perovskite • CZTS • OPV • Nanostructured • Quantum Dot

Third Generation • Tandem Cells • Multi-junction Cells • Other High-efficiency concepts

‘Three Generations of Photovoltaics’

The NREL plot……

The NREL plot (zoom)

Wafer-Silicon based technology

Step 1: Obtain good sand

Step 2: Refine (SiO2 + C Si + CO2)

Step 3: Prepare silicon bath

Step 4: Grow ingot (FZ or CZ….)

Step 5: Grind ingot (shaping for wafers)

Step 6: Saw wafers (diamond saw)

Step 7: Thickness sort

Step 8: Lapping and etching

Step 9: Sort and test

Step 10: Polish

Step 11: Qualify

Step 12: sell to PV manufacturer………….

Two main wafer types

• Crystalline silicon (C-Si) (high-efficiency)

• Multicrystalline (mC-Si) (less expensive, efficient)

Silicon Wafer Processing

Commercial Devices: Al-BSF

21% ‘Standard’ screen-printed cell 17% ‘black’ cell (1974) (NASA)

Martin Green, Philosophical Transactions of the Royal Society A, July 2013

• The ‘standard’ commercial uses no technology or design features not known in the 1970s,

• apart from the use of silicon nitride antireflection (AR) coatings, first reported in this context in 1984.

• The present standard commercial cell is essentially a ‘black’ cell with screen-printed contacts, demonstrating similar energy conversion efficiency (17–18%)

• The Passivated Emitter and Rear Contacts (PERC) started to pay more attention to the rear of the cell, most of the rear surface passivated and metal contact reduced

• The Passivated Emitter, Rear Locally-diffused (PERL) cell was the first cell to reach 25% and held the world record for most of the last 16 years.

• The PERL cell revisited the front surface with lithographically defined “inverted pyramid” structure covered with a thin passivating oxide and a double-layer antireflection coating.

UNSW: PERC and PERL cells

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Martin Green, Philosophical Transactions of the Royal Society A, July 2013

Hydrogenated PERC • PERC devices are taking an increasing share of new Si production • The most modern lines also incorporate ‘hydrogenation’ technology

• Careful thermal processing is found to activate hydrogen in the silicon and thereby passivate a range of defects that otherwise degrade devices.

• The images show Photoluminescence both before and after ‘hydrogenation’ this process brings commercial cell efficiencies from around 20% to 22%

‘Hydrogentation@unsw’ led by Prof. Stuart Wenhan (UNSW), ‘PLimaging@UNSW’ led by Prof. Thorsten Trupke (BTimaging and UNSW)

• HIT (heterojunction with intrinsic layer) cells combine a-Si technology and C-Si technology. • Unusually these devices start with an n-type substrate, but then surround the C-Si with p and n-type a-

Si layers on the top and bottom of the device. • These layers provide excellent passivation and low resistances, they ease contact formation and allow

large open-circuit voltages, • World record 25.6 % efficient devices have been demonstrated

HIT cells

• electron-hole pairs generated by light that is absorbed at the front surface can still be collected at the rear of the cell • eliminate shading losses altogether • an additional benefit is that cells with both contacts on the rear are easier to interconnect • Trina Solar recently set new large-area IBC world record at 23.5% http://www.pv-magazine.com/news/details/beitrag/trina-solar-sets-new-ibc-cell-efficiency-record_100024306/#axzz4QJ6PXce1

Rear Contact or interdigitated back contact cells (IBC)

Printing Technologies: Metallization

• Primarily revolve around metallisation screen printing or lithography • Silver is a significant ($ volatile) cost within device manufacture – ideally would be replaced by copper (electrodeposited best bet) • IBC cells required two types of contact on rear surface and this brings new challenges (for screen printing and electroplating)

International Technology Roadmap for PV (ITRPV) 2015

Printing Technologies: Optical?

• increasingly improving device performance is likely to require enhanced optical performance and micro- or nano-structured optical layers • Nano-photonic surface layers (moth-eye or Mie-scattering) to reduce reflection and/or scatter light • Back-reflector structures reflect and scatter (and thereby light-trap) • No clear (or affordable solution at present) but nano-imprinting seems best

Spinelli and Polman (Mie Scattering - nanoimprint) Bagnall and Boden (plasmonics and biomimetics)

CdTe/CdS Solar Cells (First Solar)

Cadmium Telluride/Cadmium Sulphide

• Thanks to Frist Solar CdTE/CdS remains a commercial product • 102MW solar farm in Nyngen, NSW

Both CdTe and CdS have strong tendencies to form suitable stoichiometric layers of p and n-type material as required, across large substrate areas in commercial module production – chemical bath deposition is used for the CdS

- (not all materials are this helpful!)

Printable Technologies

• When people talk about printable PV they’re mainly talking about • dye-sensitised solar cells and organic photovoltaics

• These are genuine low-temperature liquid-based printable (printed) technologies • People still hold on to the early promise of these systems • At this time neither have the efficiency to compete with silicon • OPV also lacks the durability • There are however important niche markets

‘1st Wave’: OPV and DSSC

• When people talk about printable PV they’re mainly talking about • dye-sensitised solar cells and organic photovoltaics

• These are genuine low-temperature liquid-based printable (printed) technologies • People still hold on to the early promise of these systems • At this time neither have the efficiency to compete with silicon • OPV also lacks the durability • There are however important niche markets

‘1st Wave’: OPV and DSSC

‘2nd wave’: nanospheres and microspheres

• ‘Nanosolar’ based on Copper Indium Gallium Diselenide nanospheres • ‘Nth degree’ have technology based on silicon microspheres • Spheres are suspended in a liquid and printed onto plastic substrates • Nanosolar's solar cells were verified by NREL to be as efficient 17.1% in 2011 (but efficiencies for production panels were said to be 8-9%)

• Most micro & nano approaches (including nanowires and quantum dots module efficiencies limit at 10%

• Nanosolar was a developer of solar power technology. Based in San Jose, CA, Nanosolar developed and briefly commercialized a low-cost printable solar cell manufacturing process.

• The company started selling thin-film CIGS panels mid-December 2007, and planned to sell them at 99 cents per watt, much below the market at the time.

• Prices for solar panels made of crystalline silicon declined significantly during the following years, reducing most of Nanosolar's cost advantage.

• Co-Founder stated that nanosolar "ultimately failed commercially." and that he would not enter this industry again because of slow-development cycle, complex production problems and the impact of cheap Chinese solar power production.[7]

• Nanosolar ultimately produced less than 50 MW of solar power capacity despite having raised more than $400 million in investment

Perovskites

‘3rd wave’: Perovskites

https://youtu.be/fU4PPKVF0Qw

Perovskite Devices

• improved from under 4% efficiency in 2010 to 22% in 2016

• the ‘organic-inorganic’ perovskite can be manufactured by wet chemistry (spin-coat or spray)

• fundamentally cheaper, but still small and degrade quickly

Anita Ho-Baillie team Perovskites@UNSW

30%-40% Efficiencies?

• A Perovskite-like device in tandem with a silicon cell (unlikely to be lead-halide)

• To get 30% both device technologies have to be at >20% as independent cells

• 24.5% Recently announced (UNSW, ANU, ASU, Monash, Sun-Tech, Trina)

• Silicon-wafer based solar technologies are set to dominate the photovoltaic industry for the next 10 years (at least)

• This might include 30% tandem devices

• Printing technologies have a key role in Si device technology • Printing may have increasing role in future Si cell technology - lithography for interdigitated back contact (IBC) devices - lithography for light-management - printing for module assembly? • The ‘holy-grail’ remains cells/modules based on a printed (or painted)

advanced materials • Known materials probably not good enough • there are important niches (building-integrated, consumer

electronics)

Conclusions