ennaoui cours rabat part iii
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Photovoltaic Solar Energy Conversion (PVSEC)إنتاج الكهرباء من الطاقة الشمسية
Courses on photovoltaic for Moroccan academic staff; 23-27 April, ENIM / Rabat
Q-DotsOrganic
PVSEC-Part IIIFundamental and application of Photovoltaic solar
ZnO NRs
DSSCcells and systemAhmed Ennaoui
Helmholtz-Zentrum Berlin für Materialien und Energiei@h l h lt b li d
DSSC
ennaoui@helmholtz-berlin.de
Fi t ti Sili
Highlight
First generation: Silicon Silicon PV technologyShockley-Queisser limityRoute to high efficiency solar cellsSecond Generation: Thin Films
• Substrate Chalcopyrite CIGS vs Superstrate CdTe solar cells• Substrate Chalcopyrite CIGS vs. Superstrate CdTe solar cells• Technology: CIGS module processing.• Thin layer silicon process: a-Si: H / Si
T d S l ll• Tandem Solar cell
New Concepts for Photovoltaic Energy ConversionPhotoelectrochemical and Dye-sensitized solar cellsOrganic solar cells: donor-acceptor hetero-junctionNanostructures for solar cells: photon management and quantum dots
Ahmed Ennaoui / Helmholtz-Zentrum Berlin für Materialien und Energie
p g q
Silicon the first generation
Silicon is first choice for solar cells because for good knowledge of Si processing in micro Copyrighted Material, from internet
Silicon is first choice for solar cells because for good knowledge of Si processing in micro electronics industry.
Jack Kilby (Texas Instrument)• Nobel Prize for Physics, 2000obe e o ys cs, 000• Co-inventor of the monolithic integrated
circuit (1958) – became the Si microchip.Moore's law describes a long-term trend in the history of computing hardware: the number of transistorsth t b l d i i l i t t d i it d bl i t l t N ththat can be placed inexpensively on an integrated circuit doubles approximately every two years. Now thePentium 4 has around 55 million components per chip (2003).The history of computing hardware is the record of the ongoing effort to make computer hardwarefaster, cheaper, and capable of storing more data
1941 first silicon solar cell was reported Electronics 38 (8), 114-117 (1965) 1941, first silicon solar cell was reported Efficiency less than 1%
(US Patent 240252, filed 27 March 1941)( , )Lateral Thinking: Solar cells are optoelectronic devices, they depend on the interaction of electrons, holes, and photons We need an understanding of semiconductors at the quantum mechanical level.
Brief Business ScenarioCopyrighted Material, from internet
Top 10 PV Cell Producers
Price learn curve of crystalline Si PV-modules (by Cumulative installed PV by 2007ce ea cu e o c ysta e S odu es (bydoubling the number of total installed PV power drop
prices by the same factor.
y1st Germany 3.8 GW 2nd Japan 1.9 GW3rd US 814 MW4th Spain 632 MW
Aktuelle Fakten zur Photovoltaik in Deutschland, Fraunhofer ISE / Fassung vom 8.12.2011Report from Photon International, / http://www.renewableenergyworld.com
SILICON SOLAR PV TECHNOLOGY
First generation: Silicon Solar CellsCopyrighted Material, from internet
SILICON SOLAR PV TECHNOLOGY
Production of SiMetallurgical Grade Silicon (MG) and Electronic grade (EG-Si), Metallurgical Grade Silicon (MG) is material with 98-99% purityTypical impurities (Fe), Al, Ca, Mg)Produced in about 1 Million tons per year, average price is 2 to 4 $/kgMG-Si: The sand is heated in a furnace containing a source of carbon
Reduction of SiO2 with C in arc furnace at 1800 oCMG to Si EG-Si distillation process with HCl to form SiHCl3)
Heat
Wafer based Si solar cells
Fractional distillation (impurity segregation) extremely pure SiHCl3CVD in a hydrogen atmosphere SiHCl3 into EG-Si Quartz
Crucible
Czochralski (CZ) process.Float Zone (FZ) Record efficiency solar cells.FZ is more expensive than Cz material.Si is not the best: 90% absorption requires >100 µm of Si.
Source: Eicke R. Weber, Fraunhofer-Institute for Solar Energy Systems ISE
Single Crystals: highest efficiency, slow process, high costs.Poly (multi) crystalline: low cost, fast process, lower efficiency .
Purifying the silicon: I
First generation: Silicon Solar CellsCopyrighted Material, from internet
STEP 1: Metallurgical Grade Silicon (MG-Silicon is produced from SiO2 melted and taken through a complex series of reactions in a furnace at T = 1500 to 2000 C. STEP 2: Trichlorosilane (TCS) is created by heating powdered MG-Si at around300 C in the reactor Imp rities s ch as Fe Al and B are remo ed
MicroelectronicSeebeck voltage VI
300 C in the reactor, Impurities such as Fe, Al and B are removed.Si + 3HCl SiHCl3 + H2
STEP 3: TCS is distilled to obtain hyper-pure TCS (<1ppba) and then vaporized,diluted with high-purity hydrogen, and introduced into a deposition reactor to form
l ili SiHCl + H Si + 3HCl El t i d (EG Si) 1 b I iti
Electronic Grade Chunks
Making single
HotCold
e-n-type wafer ρ = 2 π s V/I
St
d
polysilicon: SiHCl3 + H2→Si + 3HCl Electronic grade (EG-Si), 1 ppb Impurities
STEP 1
Making single crystal silicon
Czochralski (CZ) processcrucible
Seed crystal slowly grows
yp ρ
Device fabrication1. Surface etch, Texturing2. Doping: p-n junction formation
CellsSTEPE 2 and 3
Ingot sliced 3. Edge etch: removes the junction at the edge4. Oxide Etch: removes oxides formed during diffusion5. Antireflection coating: Silicon nitride layer reduces reflection
Source: Wacker Chemie AG, Energieverbrauch: etwa 250kWh/kg im TCS-Process, Herstellungspreis von etwa 40-60 €/kg Reinstsilizium
to create wafers
First generation: Silicon Solar Cells
Anti-Reflection CoatingCopyrighted Material, from internet
gSi3N4 layer reduces reflection of sunlight and passivates the cell
plasma enhanced chemical vapor deposition (PECVD)) .
First generation: Silicon Solar CellsCopyrighted Material, from internet
Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon.
Screen Printer with automatic loading and unloading of cells
First generation: Silicon Solar CellsCopyrighted Material, from internet
Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon.
.
Firing furnace to sinter metal contacts
Not all the energy in each absorbed photon can be captured for productive use. U d AM1 5 t l di t ib ti Si l j ti l ll h i l i ffi i f 32%
Shockley-Queisser limit Copyrighted Material, from internet
Under AM1.5 spectral distribution: Single-junction solar cell has a maximal conversion efficiency of ~32% Solar Energy Materials & Solar Cells 90, 2329-2337 (2006)
1.8%0.4% 0.4%
I2R LossReflection Loss
0.4%
1.54% 3.8%
%
0.3%
RecombinationLosses
1.4%2.6%
2.0%Back LightAbsorption
(1) L tti th li ti l (> 50%)(1) Lattice thermalisation loss (> 50%)(2) Transparency to photons loss < Band gap(3) Recombination Loss(4) Current flow(5) Contact voltage loss
Source: University of Delaware, USA
Shockley-Queisser limit Copyrighted Material, from internet
Low reflection Low recombination, High carrier absorption
Technology approach to high efficiency solar cellsCopyrighted Material, from internet
Thinner emitter, closed spaced metal fingersBack surface field (p+-p )Anisotropic texturing (current collection)Surface Passivation (SiO ca 0 01 m) Key to obtain V : Surface Passivation (SiO2 ca. 0,01 μm) Key to obtain Voc: Photolithography to have small contact area and high aspect ratioLaser grooving and electroplating of metal.
TiO SiO Z S M FTechnological loss
Resistive lossnARC ARCTexturing
ARCARC n4
1N2d +=
TiO2, SiO2, ZnS, MgF2
Reflection lossTop contact
High doping
n2
Recombination loss ‐‐
EBSF
High doping
Traditional cell design
Route to high efficiency solar cells Copyrighted Material, from internet
Traditional cell design PERLPERCIBCPESCTraditional cell design PERLPERCIBCPESCMINP(1) PERL developed at UNSW (EFF. 25%) Passivated Emitter and Rear Locally diffused1
(2) Localized Emitter Cell Using Semiconducting Fingers. (EFF. 18.6%, CZ n-type)(3) Laser-grooved, buried front contact (LGBC; EFF. 21.1%)
n+
n++
(1)Buriedcontact
Back contact
n++ P
(2)
(3)1 Martin Green, PIP 2009; 17:183–189, University of New South Wales, Australia http://www.unsw.edu.au/
Route to high efficiency solar cellsThickness of the c-Si absorber without reflectivity and recombination losses
Copyrighted Material, from internet
⎟⎟⎠
⎞⎜⎜⎝
⎛
+−−= −αW
p
eαL111 R)(1 η
⎤⎡
y
{ {∫ ⎥⎥
⎦
⎤
⎢⎢
⎣
⎡−λ=
GE Light Absorbed
λλ
flux Photon
0light Collectionarea Cell
sc dλ .dα-exp . )R(1 . )(Φ . η(λ). q . AI444 3444 21321
Route to high efficiency solar cellsThe space charge region and tunneling at metals/highly doped semiconductor junction
Copyrighted Material, from internet
Quantum MechanicsHighly doped semiconductor
(n++ , p++ = 1020...1021 carriers/cm3)
Tunneling
Route to high efficiency solar cells Copyrighted Material, from internet
1 R f Δn Δp1. Rsurf Δns ,Δps2. Rsurf vns ,vps Nts
1. Reduction of the minority carrier concentration at the Ohmic ycontact (realized with the back surface field - BSF).
2. Reduction of the Ohmic contact area and reduction of thesurface recombination velocity at the non Ohmic contact Si surfaces (realized with contact grids and surface passivation)Si – surfaces (realized with contact grids and surface passivation)
Route to high efficiency solar cellsWhat is exactly a passivation?
Copyrighted Material, from internet
y p
Most important interface in the world passivating properties observed in 1960 applied in the world record Si solar cell
Route to high efficiency solar cellsBSF: Back Surface Field: The electric field back is to create a potential barrier
Copyrighted Material, from internet
BSF: Back Surface Field: The electric field back is to create a potential barrier (e.g. p+-p junction) on the rear of the cell to ensure passivation.The potential barrier induced by the difference in doping level between the base and the BSFtends to confine minority carriers in the base.These are therefore required to away from the rear face which is characterized by a very high rate of recombination. Fabrication tools: Diffusion furnace, PECVD, RTP, Screen-printer, Belt furnace, FZ wafers, boron-BSF sample, and screen-printing pastesboron BSF sample, and screen printing pastes
SiN/SiO2Ag gridlines
n+ emitter
p-Si
n+ emitter
Al-Si eutectic
Al/Ag rear contact
BSF
SiN/SiO2
Record efficiency=26.8% at 25W/cm2 IrradianceSource: University of Delaware SunPower’s Backside Contact Cellhttp://www.sunpowercorp.de/about/
Route to high efficiency solar cellsMetal-Wrap-Through Solar Cell
Copyrighted Material, from internet
Metal Wrap Through Solar Cell
Photovoltech is commercializing the MWT solar cell; efficiencies ~ 15%
Source: University of Delaware
Route to high efficiency solar cellsThe Sliver® Solar Cell
Copyrighted Material, from internet
The Sliver Solar Cell
Origin Energy (Australia) is commercializing the Sliver® Solar Cell (cell efficiencies 20%)
Source: University of Delaware
Route to high efficiency solar cells
R I t di it t d Si l E ti E itt W Th h
Copyrighted Material, from internet
Rear Interdigitated Single Evaporation-Emitter Wrap Through
• Both contacts on the rear• N h d i th f t• No shadowing on the front• Carrier collection on two sides • Rear-side SiO2 passivation• Laser processing for
grooves, holes and
ISFH lab result on 10x10 cm2
η = 21% contact openings• Single Al evaporation
η 21%
Source: Institute for Solid State Physics , Leibniz University of Hanover/22nd EU-PVSEC (2007)
Roadmap: Different Generation of Solar cells and PV Power Costs First-generation - based on expensive silicon wafers;
UltimateThermodynamic
limit at 1 sun
First generation based on expensive silicon wafers; 85% of the current commercial market.Second-generation - based on thin films of materials such as amorphous silicon, nanocrystalline silicon, cadmium telluride, or copper indium selenide. The at 1 sun
Shockley-Queisser limit
cadmium telluride, or copper indium selenide. The materials are less expensive, but research is needed to raise the cells' efficiency.Third-generation - the research goal: a dramatic increase in efficiency that maintains the cost increase in efficiency that maintains the cost advantage of second-generation materials. Their design may make use of carrier multiplication, hot electron extraction, multiple junctions, sunlight concentration or new materials
Efficiency and cost projections for first-, second- and third- generation photovoltaic technology (wafers, thin-films and advanced thin-film respectively. The horizontal axis represents the cost of the solar module only; it must be approximately
doubled to include the costs of packaging and mounting. Dotted lines indicate the cost per watt of peak power.
concentration, or new materials.
f ff fAdvanced Research for achieving high efficiency from inexpensive materials with so-called third-generationConcentrating sunlight allows for a greater contribution from multi-photon processesStacked cells with different bandgaps capture a greater fraction of the solar spectrumCarrier multiplication is a quantum-dot phenomenon that results in multiple electron–hole pairs for a single incident photonHot-electron extraction provides way to increase the efficiency of nanocrystal-based solar cells by tapping off energetic electrons and
Martin Green , Prog. Photovolt: Res. Appl. 9, (2001) pp 123-135
Hot electron extraction provides way to increase the efficiency of nanocrystal based solar cells by tapping off energetic electrons andholes before they have time to thermally relax.
various thin-film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creatinga solar cell. This can lead to reduced processing costs
Basic: different ways to make a solar cells / Low cost processing Thin layer techniques Copyrighted Material, from internet
Vacuum evaporation
Physical techniques
Reactive deposition
Chemical techniques
Self-assembling
Solvent based techniques Electrochemical techniques
Electroplating
Epitaxial deposition
Laser deposition
Sputtering
Gel processing
Chemical vapour deposition
Langmuir-Blodgett
Spray methods
Doctor blading
Spin coating
Electrophoresis
Ion-assisted deposition Ionized cluster beam
IonizationFlow coating
Dip coating
Fl i ti G i ti
Printing
Flexo printing Gravure printing
Ink jet printing Offset printing
Microcontact printing Relief printing
Screen printingScreen printing
KesteriteInk
Electrophoresis
Spin coating
How do NPs form?Projekttreffen NanoPV Vertraulich/Patent pending
R. Schurr et al. Thin Solid Films 517 (2009) 2465–2468Vertraulich/Patent pending A. Ennaoui et al. Thin Solid Films 517 (2009) 2511–251
A. Ennaoui, Lin, Lux-Steiner PVSEC 2011Kesterite
Ink
Chemical reaction takes place
Critical concentrantion, nucleation begins
Aggregation happens due to its lowering the free energy
Particles grow and consume all the solute
Best time to synthesize
Hot injectionsynthesis
Subsequent growth of the nuclei lowers the solute concentration
Best time to synthesize nanoparticles
synthesis
http://www.authorstream.com/Presentation/rahulpupu-976297-nanoparticles/
Nanostructured ZnO From microstructure to nanorodes and fuctionalization Ennaoui ´Group: Jaison Kavalakkatt, PhD/FU Berlin
Confidential /IP, Patent Pending
Non Vacuum processing / Low Cost Equipments next generation solar cells
Changing electrochemical conditionTEM
HRTEMM
5 nm
M
100 nm
See Concept of Inorganic solid-state nanostructured solar cellsSpecial issue Ahmed EnnaouiSolar Energy Materials and Solar Cells, Volume 95, Issue 6, June 2011, Pages 1527-1536
Ahmed Ennaoui / head of a research group: Thin Film and nanostructured solar cells /Solar Energy Division / Helmholtz-Zentrum Berlin für Materialien und Energie
Heterojunction amorphous silicon / crystalline silicon (a-Si: H / Si)
Thin layer silicon process: (a-Si: H / Si) Copyrighted Material, from internet
Heterojunction amorphous silicon / crystalline silicon (a-Si: H / Si), say HIT with intrinsic Thin Layer Two heterojunctions a-Si: H / Si: The "front heterojunction is the" transmitter, while the second, the rear panel, acts as a field of repulsion or BSF., p , pIntrinsic zone allows "better" surface quality at the junction layer .transparent conductive oxide (TCO) is deposited to ensure good contact between the amorphous layer and the metal.The heterojunction is obtained by depositing technologically "a layer a few “nm” hydrogenated amorphous silicon, a-Si: H.
Basic: Tandem Cell)
EFF Lab 12 13% / Module 10%
Copyrighted Material, from internet
EFF. Lab 12-13% / Module 10%
Back Reflector
Thin film mc-Si
a-Si
Thin film mc SiBottom cell
Textured TCO
a-Si Top cell
Glass substrate
S Li h
Practical Handbook of Photovoltaics: From Fundamentals to Applications, edited by T. Markvart and L. Castaner. Oxford: Elsevier, 2003
Sun-Light
Multijunction cells use multiple materials to match the spectrum
Basic: Efficiencies beyond the Shockley-Queisser limitCopyrighted Material, from internet
Multijunction cells use multiple materials to match the spectrum.The cells are in series; current is passed through deviceThe current is limited by the layers that produces the least current.The voltages of the cells addThe higher band gap must see the light first.By making alloys, all band gaps can be achieved.Challenge: Lattice matched limited in material combinationsGaInP/GaInAs/Ge Cells record 38.8% @ 240 suns (2005)
GaInP/GaInAs/Ge Cells have powered Mars Exploration Rovers (MER)
New?
(R. King, et al, 20th PVSEC European Conference)
Basic: Efficiencies beyond the Shockley-Queisser limitStructure of Triple-Junction (3J) Cell
Copyrighted Material, from internet
AR Coating Front Contact
I G P
n+ (In)GaAsn+ AlInP [Si]+ I G P [Si]
• Efficiencies up to 41%
Tunnel Junction
InGaPTop Cell
n+ InGaP [Si]p InGaP [Zn]p AlInP [Zn]p++ AlGaAs [C]n++ InGaP [Si]
• Six different elements
InGaAs Middle Cell
n InGaP [Si]n+ AlInP [Si]n+ (In)GaAs [Si]p (In)GaAs [Zn]p+ InGaP [Zn]
• Three different dopants
• Practically used:
Buffer Layer
p [ ]p++ AlGaAs [C]n++ InGaP [Si]
n+ GaAs : 0.1µmn+ (In)GaAs [Si]
Tunnel Junction
G
• Practically used: 3-junction cells
Back Contact
p Ge Substraten Ge
Bottom Cell• Research:
4 to 5 junctions
Yamaguchi et. al., 2003 Space Power Workshop
2nd. Generation: Cu(In,Ga)(S,Se2) Chalcopyrite solar cell
IV The chalcopyrite structure can be deduced from theDiamond SiIV diamond structure according to the Grimm-Sommerfeld-rule,
which states that a tetragonal structure is formed, if theaverage number of valence electrons per atom equals four
Diamond structure
E i i l fil
III-V II-VIP l lli
zincblende structure 4...
=++
+mn
mqnq MN
N M elementsEpitaxial film: GaAs , InP…
Polycrystalline thin film:
CdTe, ZnS
N,M elementsn,m atoms/unit cell
qN, qM valence electrons
Polycrystalline thin film:
I-III-VI2Epitaxial film:
Z G A
II-IV-V2
y yCu(In,Ga)(Se,S)2
(Chalcopyrite and related compounds)
I III VI Alloy: Group I= Cu
ZnGeAs, …
I-III-VI2 Alloy: Group I= Cu, Group III= In and Ga, Group VI = Se and S
Possible combinations of (I, III, VI) elements
⎞⎛Sn ⎞⎛Ga⎟⎞
⎜⎛Cu
Z
⎟⎟⎠
⎞⎜⎜⎝
⎛ZnSn( )In
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
AlInGa
⎟⎟⎟⎞
⎜⎜⎜⎛SeS
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
AuAgCu
B 5 C 6 N 7 O 8 F 9Li3 Be 4
Zn 26
1.2251.5
ElementTetrahedral coordination radiusElectronegativity IIIa VIa
Cu(In,Ga)Se2
⎠⎝ Al2
⎟⎠
⎜⎝Te⎠⎝
Al13 Si 14 P 15 S16 Cl 173s
2s 2p
1.230
0.853 0.774
1.173
0.719
1.128 1.127
0.678 0.672
1.127
2.0 2.5 3.0 3.5 3.9
Na 11 Mg 12
2s2p
33s
0.975
1.301
1.50.95
Cu29 Zn 30 Ga31 Ge 32 As 33 Se34 Br 35
3p
3d 4s 4p
1.225 1.225 1.225 1.225 1.225 1.225 1.225
3.0
2.81.8 1.5 1.5 1.8 2.0 2.4
2.52.11.81.5
K 19 Ca 20
3p
4p4s3d
1.333
1.2
1.0
0.9
0.8
Ib IIb
Ag 47
Au79
Cd48
Hg80
In49
Tl81
Sn 50
Pb82
Sb 51
Bi83
Te52
Po84
I 53
At85
4d 5s 5p
5d
1.405 1.405 1.405 1.405 1.405 1.405 1.405
2.52.11.81.71.51.51.8
Rb 37
Cs55
Sr 38
Ba56
5p5s4d
5d
1.6891.00.8
Au 79 Hg 80 Tl 81 Pb 82 Bi 83 Po 84 At 85 5d 6s 6p2.3 1.8 1.5 1.8 1.8 2.0 2.2
Cs 55 Ba 56
6p6s5d
0.75 0.91.392
Second Generation: Thin-film Technologies• Advantage: Low material cost, Reduced mass
Di d t T i t i l (Cd) S t i l (I T )Copyrighted Material, from internet
• Disadvantages: Toxic material (Cd), Scarce material (In, Te)• CdTe – 8 – 11% efficiency (18% demonstrated) • CIGS – 7-11% efficiency (20% demonstrated)
CdTe based deviceSource: Rommel Noufi, NREL, Colorado, USA, http://www.nrel.gov/learning/re_photovoltaics.html
*CIGS based device
Potentials of thin film Cu-chalcopyrite technologies
1 S tt i f C d I1. Sputtering of Cu and In2. Rapid Thermal processing (RTP)
• low material consumtions
• low energy consumptionhi h d i i l• high productivity large area
• „monolithic“ interconnects - Laser• new products (e.g. flexible cells)
f substratewaferWafer based technology
substrateThin film cell structure thickness 1.5-2 µm
Source: HZB / Technology department
Quelle: EI3
Potentials of thin film Cu-chalcopyrite technologies
Cu
In
S
1 kWp : Comparison of c-Si and CuInS2
Source: HZB / Technology department
Module processing
1. KCN etching2. CBD-Buffer
Source: HZB / Technology department
Monolithic integration for series connection of individual cells
Technology: Module processingMonolithic integration for series connection of individual cells
P1: Series of periodic scribes that defines the width of the cells
P2: After the absorber and buffer layer deposition Pulsed LaserP2: After the absorber and buffer layer deposition
P3: After the window deposition P1Pulsed Laser
Front ZnO of one cell connected to the CIGS
BufferZnO
+Ga +Se
connected to the back Mo contact of
the next GlassMoCIGS
1. Deposition of Cu, In,Ga1. Deposition of Cu, In,Ga2. RTP/Reaction with S/Se
Source: HZB / EI2 department
Monolithic integration for series connection of individual cellsTechnology: Module processing
+-
Loads
CIGSCdSi-ZnOZn:Al
Glass
Mo
P1 P2 P3
+ + ++
Laser scribing and mechanical scribingpulse repetition rate i Z O/Z O Al
RSC
pulse repetition ratepulse powerwavelength and spot diameterElectrical isolation for front and back contact scribesCIGS
CdS
i-ZnO/ZnO:Al
+
Low series resistance for the interconnect scribeInterconnect resistivity as low as possibleGlass
Mo
Source: ZSW
Substrate: soda lime glass coated with Mo
Best efficiency from annealing of stacked metal layers
Temperature/°CSubstrate: soda lime glass coated with MoDeposition of Cu and In, Ga layers by sputteringDeposition of Se layer by evaporationRapid thermal process (RTP)
Temperature/ C
500-550
RTPRapid thermal process (RTP)
Advantage: Design of production facilitiesLarge area deposition Avoidance of toxic H Se
Time/min
RTP
Large-area deposition Avoidance of toxic H2SeThe most essential factor that decides if the absorber is going to result in a high-efficiency device, is its Cu content, or the Cu/(Ga+In) ratio
Cu(In.Ga)(S,Se)2
CIGS film should be slightly Cu deficient with a thin even more Cu deficient surface CIGS film should be slightly Cu-deficient, with a thin, even more Cu-deficient surface layer. This surface layer corresponds to the stable ordered vacancy (OVC) Cu(In,Ga)3Se5.
Fundamental understanding
ZnOZnO
Absorber
Fundamental understanding
ZnOZnOEC
E
EC < EC
buffer CIS?
ZnS at
AbsorberCIS, CIGS
EV
AZnO
The GBs
BufferBarrier for recombination:
Al
O
Absorber
Simplified version of the ternary phase diagramMaterial Properties: Phases Diagram
Copyrighted Material, from internet
Reduced to pseudo-binary phase diagram along the red dashed lineBold blue line: photovoltaic-quality materialRelevant phases: α- β- γ- δ-phase and Cu2SeRelevant phases: α , β , γ , δ phase,and Cu2Se
CuIn3S5Not
found
α: chalcopyrite CuInSe2β: defect chalcopyrite Cu(In,Ga)3Se5
γ: Cu(In,Ga)5Se8
α-phase (CuInSe2):Material Properties: Phases Diagram
Copyrighted Material, from internetα phase (CuInSe2):
• Optimal range for efficient thin film solar cells: 22-24 at %• α-phase highly narrowed @RT• Possible at growth temp.: 500-550°C, @RT: phase separation into α+βPossible at growth temp.: 500 550 C, @RT: phase separation into α β
β-phase (CuIn3Se5)β phase (CuIn3Se5)• built by ordered arrays of defect pairs• anti sites (VCu, InCu)
δ-phase (high-temperature phase)• built by disordering Cu & In sub-lattice
Cu2Se• built from chalcopyrite structure by• Cu interstitials Cui & CuIn anti sitesCu interstitials Cui & CuIn anti sites
Hamakawa, Yoshihiro: Thin Film Solar Cells, Springer, 2004.
Material Properties: Impurities & Defects
Partial replacement of In with Ga; 20-30% of In replaced: Ga/(Ga+In) ~ 0.3 Partial replacement of In with Ga; 20 30% of In replaced: Ga/(Ga In) 0.3 Band gap adjustment: 1.03eV-1.7 eV
Incorporation of 0.1 at % Na N (S ) ( t bilit d ith ↑)
- Widening of bandgap at the surface of the film
The surface composition of Cu poor CIGS Na2(Se)1+n (stability decrease with n↑)Better film morphologyPassivation of grain-boundariesHigher p-type conductivity
- The surface composition of Cu-poor CIGS films
(Ga+In)/(Ga +In+Cu) ca. 0.75 - The bulk compositions g p yp y
Reduce defect concentrationThe are many defect
- 3 vacancies: VCu, VGa, VSe.3 i t titi l C G S
The bulk compositions 0.5< (Ga+In)= (Ga+In+Cu) < 0.75.
Phase segregation of Cu(In,Ga)3Se5- 3 interstitials: Cui, Gai, Sei.- 6 antisites:
CuGa, CuSe, GaCu, GaSe, SeCu, SeGa
Phase segregation of Cu(In,Ga)3Se5occurs at the surface of the films.
Ordered-Vacancy/ Defect Compounds (OVC/ODC)Ordered or disordered arrays of vacancies are occupying the cation sites They can exceed the local range of the unit cell, we called vacancy compoundsSuperlattice structures of the ideal chalcopyrite, reported as stable phases: OVC/ODCOVC/ODC are observed in slightly Cu-deficient: Cu(In,Ga)3Se5
Schock, Rommel Noufi, , Prog. Photovolt. Res. Appl. 8, (2000) pp. 151-160
Roll-to-Roll deposition (R2R)Ion beam supported low temperature
f C G SSource: Fahoum Mounir/Habilitation
Substrate:Mo coated polyimide/ stainless steel foil
(F f th b t t ?)
deposition of Cu, In, Ga, Se
Alternative ElectrochemistryAdvantages:
• Low cost production
(Fe from the substrate?)
• Low cost production• Flexible modules • High power per weight ratio
Voltage
AnnealingIn,Ga,Cu -ions
- +
G C I S Buffer TCOAnnealing, ,Ga,Cu, In, Se
Recombination mechanism issue
⎞⎛⎟⎟⎠
⎞⎜⎜⎝
⎛−=
SC
aOC j
jq
nkTq
EV 00ln⎠⎝
A: Diode quality factorEA: Activation energy
B ff
Cu(In,Ga)Se2EC
J00 : Prefactor, weakly temperature-dependent
(1): interface recombination
E = Φ
BufferEg
EF
2
Ea = Φb
(2): bulk recombination ΦbEV1
Ea = Eg
Conversion efficiencies achieved by CuInS2 (EG
Important Remarksy 2 ( G
= 1.53 eV) or CuGaSe2 (EG = 1.7 eV) absorbers are considerably lower than those achieved by low band gap Cu(In Ga)Se or even CuInSe OVC
p-Cu(In,Ga)Se2Burried pn-junction
low band gap Cu(In,Ga)Se2 or even CuInSe2.
Why?
OVCp ( , ) 2
OVC
I l b d C (I G )S•Formation of weakly n-type OVC layer•The bulk is p-type
In low band gap Cu(In,Ga)Se2
p yp•Buried p-n junction
n-Cu(In,Ga)3Se5ΔEVn
OVC minimizes the recombination at the CIGS/buffer interface.OVC surface layer has direct and wider band gap than the bulkOVC increases further the barrier Φ for recombination at CIGS/CdSOVC increases further the barrier ,Φ, for recombination at CIGS/CdS
That is the key to high-efficiency solar cells.
Third Generation: MultiThird Generation: Multi--junction Cellsjunction CellsCopyrighted Material, HZB
Technology: CIGS module processing
N. Naghavi, D. Abou-Ras, N. Allsop, N. Barreau, S. Bu¨ cheler, A. Ennaoui, C.-H. Fischer, C. Guillen, D. Hariskos, J. Herrero, R. Klenk, K. Kushiya, D. Lincot, R. Menner, T. Nakada, C. Platzer-Björkman, S. Spiering, A.N. Tiwari and T. Törndahl. Prog. Photovolt: Res. Appl. (2010). Published online in Wiley InterScience, Vol. 18, issue 6 (2011) pp. 411-g pp ( ) y , , ( ) pp433
The world record chalcopyrite solar cell
Cu(In,Ga)Se2
New Concepts for Photovoltaic Energy Conversion(Photo)electrochemical and Dye-sensitized solar cellsOrganic solar cells: donor-acceptor hetero-junctionOrganic solar cells: donor-acceptor hetero-junctionNanostructures for solar cells
Semiconductor/Liquid versus Semiconductor/Metal Junction
Vacuum level0
Φ χ qχ
E
CBCB
EF,SC
EF,SC
χ
qΦΜ
qVB
0H+/H2
EF,Metal
EC
EF,SCBack contact
MetalCE
EC
EF,SCBack contactEF,redox
qVBB
- 4.5 eV
SCE
1.23VH2O/H2
EV
contact
Semiconductor (WE)
EV
VB VB
RedoxElectrolyte
SCE+0.243V
V vs. NHE
EV V
Semiconductore.g. TiO2
Semiconductore.g. Si
e.g. I-/I2 Metale.g. Au
Electrochemical scale Solid state scale
Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Semiconductor/Liquid versus Semiconductor/Metal Junction
Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Semiconductor/Liquid versus Semiconductor/Metal Junction
Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Photoelectrochemical Solar Cell (PECs): Photovoltaic modeCopyrighted Material, from internet
‐
Reduction
Sc M‐+
Reduction
I2 + e‐Back
contact Countre +
Oxidation
I‐ + h+ Electrode(CE)
I‐ + h+ I2 + e‐I‐ + h+ I2 + e‐
Electron and holes are photogeneratedHoles are moved to the surface of the WE
react with I--Electron are moved to the back contact
t ith I i th th id (CE)
I‐ + h+current
V
Source: A.J. Nozik, National Renewable Energy Laboratory
reacts with I2 in the other side (CE)I2 + e‐
Voltage vs. redox
Solar cells that mimic plants
Light absorption DyeChlorophyll Light absorption
e- transfer
Hole transfer
y
Semiconductor oxide (TiO2)
Electrolyte
p y
Charge transfer protein
Proton pump Hole transfer ElectrolyteProton pump
Copyrighted Material, from internet
Solar cells that mimic plants: DSSCCopyrighted Material, from internet
HOMO
LUMO
CO2
SugarH O
Photosynthesis
H2OO2
The most widely used sensitizer abbreviated as N3.
source: partly http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell
y“cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)”
Grätzel, M., Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 145
Solar cells that mimic plants: DSSC
HOMO: highest occupied molecular orbital
Copyrighted Material, from internet
HOMO: highest occupied molecular orbital
LUMO: lowest unoccupied molecular orbital
HOMO
LUMO
CO2
SugarH O
Photosynthesis
H2OO2
The most widely used sensitizer abbreviated as N3.
source: partly http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell
y“cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)”
Grätzel, M., Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 145
Solar cells that mimic plantsFew simple materials and you can create your own Grätzel Cell
Copyrighted Material, from internet
Ru(II) + hν → Ru(II)*
The most widely used sensitizer abbreviated as N3. “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)”
Ru(II)* → Ru(III) + e-
I3- + 2e-→ 3I-
3I- + Ru(III)→ I3- + Ru (II)
DSSCModule
I‐ + h+
Module
I2 + e‐
Generation Transport B k ti ( ) ith I
Solar cells that mimic plants Copyrighted Material, from internet
( )20
2x
n
n nn nIe Dt x
αατ
− −∂ ∂= + −
∂ ∂
Generation Transport Back reaction (c) with I3-
τn = 1/kcb [I3-]
nt x τ∂ ∂*(
II))
Ru(
III)/R
u
(b)
(II)/R
u(II)
)(c) (a)( )
Ru*
Solar cells that mimic plants: DSSCCopyrighted Material, from internet
http://www.solaronix.com/
Mesoporous TiO2 anatase
Efficiency of 10 % was obtained by the solar cells assembled at the EPFL in Lausanne (simulated sunlight AM 1.5, 1000 W/m2) Eff. = 10 %, AM 1.5, VOC = 823 mV, ISC = 16.9 mA/cm2, FF = 72.5 %)Download Dye Solar Cells Assembly Instructions @ : http://www.solaronix.com/technology/assembly/
Nanocrystalline based Solar cells
Electron holes photogeneratedCopyrighted Material, from internet
Electron holes photogenerated Immediately injected in mesoporous TiO2 (or ZnO NRs)
J B Sambur et al. Science 2010;330:63-66Band energy diagram indicating the relevant energy levels
T. Dittrich, A. Belaidi, A. Ennaoui
ZnOnanorodes
Band energy diagram indicating the relevant energy levels and kinetic processes that describe PbS QD ET and HT into
the TiO2 conduction band and the sulfide/polysulfide electrolyte, respectively.
Extremely Thin AbsorberConcept of Inorganic solid-state nanostructured solar cells
Solar Energy Materials and Solar Cells, Volume 95, Issue 6, June 2011, Pages 1527-1536
Photoelectrochemical solar cells (PECs) Photoelectrolysis mode
1/C2 Band gap must be at least 1 8 2 0 eV Lock‐in Potentiostatv=vmeiωt
V+v(t)
WE CERE
1/C
VVb
Band gap must be at least 1.8-2.0 eV But small enough to absorb most sunlightBand edges must straddle Redox potentialsFast charge transfer
Material requirementsWE CERE
Determination of Flat Band Potential (Vfb)
hν>EI
Fast charge transferStable in aqueous solution
E
hν>EG V
1.23eV
EC
EF,SCBack contact
Metal
EF,redox (CE) 1.23eV
WE CERE
EV (WE) Elec
trolyt
eAnode: 2H20 4e- + 02 + 4H+
V ( ) E
A. Ennaoui and et al. Solar Energy materials and Solar Cells Volume 29 (1993), Pages 289-370This lecture was presented @ Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Cathode: 4H20 + 4e- 4OH- + 2H2
Determination of Flat Band Potential (Vfb)
Lock‐in Potentiostatv=vmeiωt
V+v(t)
WE CEREWE CERE
vacuum
0
H+/H2
A. Ennaoui and et al. Solar Energy materials and Solar Cells Volume 29 (1993), Pages 289-370This lecture was presented @ Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Ref.
Materials suitable for solar PECsCopyrighted Material, from internet
Photoelectrochemical solar cells (PECs) Photoelectrolysis mode
D
D
DDDDDD
D
H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol
Source: Mildred Dresselhaus, Massachusetts Institute of Technology
d0 and d10 metal oxidesCopyrighted Material, from internet
GaN-ZnO (Ga1-xZnx)-(N1-xOx)
d0
Ti4+: TiO2 SrTiO3 K2La2Ti3O10
d10
Ga3+: ZnGa OTi : TiO2, SrTiO3, K2La2Ti3O10Zr4+: ZrO2Nb5+: K4Nb6O17, Sr2Nb2O7Ta5+: ATaO3(A=Li, Na, K), BaTa2O6
6 ( b b )
Ga3 : ZnGa2O4In3+: AInO2 (A=Li, Na)Ge4+: Zn2GeO4Sn4+: Sr2SnO4
W6+: AMWO6 (A=Rb, Cs; M=Nb, Ta) Sb5+: NaSbO7
N replaces O in certain positions, providing a smaller band gap.Problems with getting the nitrogen there without too many defects.O f ti T N G NOxygen free options: Ta3N5, Ge3N4
Domen et al. New Non‐Oxide Photocatalysts Designed for Overall Water Splitting under Visible Light. J. Phys. Chem. 2007
Use of PV for H2 productionHydrogen and Oxygen are produced using photovoltaic effect
Test of security
y g yg p g p
p n p n p n
Test of security- No damage to hydrogen car- Gasoline car completely destroyed
p n p n p n
Solid state solar cells
OO22 HH22
HH22OO
HH++
e- e-
Source: Partly A.J. Nozik, National Renewable Energy Laboratory
OODark electrolysis cell
Water splitting: Hydrogen productionChallenge: Material requirement :
Copyrighted Material, from internetChallenge: Material requirement :
Material/catalysts, nano-materials, membranes (need Brainstorming )Understand and control the interaction of hydrogen with materials
Source: Mildred Dresselhaus, Massachusetts Institute of Technology millie@mgm.mit.edu
H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol
Fuel Cells
Fuel Cell uses a constant flow of
Copyrighted Material, from internet
Fuel Cell uses a constant flow of H2 to produce energy.Reaction takes place between Catalyst = Pt Very expensive
Minimize the Pt quantityH2 and O2 electrical energy.The most common fuel cell usesProton Exchange Membrane, or PEM
q yImprove the active layer structurePropose new materials
oto c a ge e b a e, oNeed of catalyst (e.g. platinumfor a reaction that ionizes the gasO is ionized to O2-O2 is ionized to O2
H2 is ionized to 2H+
2H+ + O2- = H2OO2- and H+ combine
Energy is given off inelectron form and givesoff power to run an engine
The “waste products” are water and heat
off power to run an engine
AdvantagesAdvantages and Challenges Copyrighted Material, from internet
AdvantagesZero emissionNo dependence on foreign oilAbilit t h t l d bl Ability to harvest solar and renewable energyNot many moving part in a carHydrogen weighs less than gasoline y g g g
car would not need as much energy to move
ChallengesgStill expensive to equip a car with a hydrogen fuel cell. Hydrogen is expensive to make, store, and transportThe center is a platinum plate which is very expensiveThe center is a platinum plate which is very expensiveNational Program in USA since 2007: 1 billion dollars to date in hydrogen car research for the “develop hydrogen, fuel cell and infrastructure technologies to make fuel-cell vehicles practical and cost-effective by 2020.”
Basic: Brief Business Scenario Copyrighted Material, from internet
1999 FOUNDED, 2001 BEGAN WITH THE PRODUCTION OF SILICON SOLAR CELLS WITH 19 EMPLOYEES.
BY 2009, 2,600 EMPLOYEES (2007, 1700 EMPLOYEES)
NOW THE LARGEST SOLAR CELL MANUFACTURER IN THE WORLD (SINCE 2007)NOW THE LARGEST SOLAR CELL MANUFACTURER IN THE WORLD. (SINCE 2007)CONTINUE TO EXPAND PRODUCTION IN BITTERFELD-WOLFEN, GERMANY AND
START CONSTRUCTION OF NEW MALAYSIAN PRODUCTION FACILITY. ALONGSIDE THE MONO-CRYSTALLINE AND POLYCRYSTALLINE (90% OF
BUSINESS) CORE BUSINESS, WE USE A WIDE RANGE OF TECHNOLOGIES TO DEVELOP AND
PRODUCE PRODUCE THIN-FILM MODULES. (THIN-FILM - 25% SHARE OF SMALLER MARKET)Year over year, Q-Cells SE has been able to grow revenues from €790.4M to €1.4B.
http://investing.businessweek.com
SunTech Power (China)
Basic: Brief Business ScenarioCopyrighted Material, from internet
- THE COMPANY WAS FOUNDED IN 2001 BY ZHENGRONG SHI- SALES $1.9B 2008, 1.3B 2007 PROFITABLE- EMPLOYEES: 6784- WORLDS LARGEST SILICON CELL MAKER
SunTech Power (China)
WORLDS LARGEST SILICON CELL MAKER- AVERAGE CONVERSION EFFICIENCY RATES OF THEIR - MONOCRYSTALLINE AND MULTICRYSTALLINE SILICON PV CELLS - 16.4% AND 14.9% RESPECTIVELY- 2009 ANNOUNCES PLAN TO BUILD MANUFACTURING PLANT IN US
130KW
Zhengrong Shi Boen in 1963 inChina, finished his Master inChina then he went to Universityof New South Wales (Austria). He
14MWNevada
8MWNevada
5.1MWSpanien
43KWSpanien
0.092-0.3-3.8MWGermany
10 MWAbu Dhabi
3MWChina
China( )
obtained his doctorate degree onsolar power technology andreturned to China in 2001 to setup his solar power company (Networth US$2.9 Billion (2008)
500KWNevada
48KWAustralien
http://eu.suntech-power.com
130MWCapacityCapacity
Copyrighted Material, from internet
130MWCapacity Capacity Expansion Expansion
55MW70MW
R&D
30MW20MW
Kaneka has been specializing in thin-film silicon technology:1980 Started study of a-Si technology
1980 20081999 2006 2007 2010
1987 Participated in NEDO project (Government funded R&D)1999 Started 20MW/yr commercial production2006 Announced capacity expansion:
- up to 30MW in 2006, 55MW in 2007, 70MW in 20082007 Introduction of new Hybrid PV
Announced capacity expansion: up to 130MW in 2010
Copyrighted Material, from internet
Excitonic solar cells
Exciton
Copyrighted Material, from internet
ExcitonelectronsLUMO
holesholes
HOMOInterface
• all organic: polymer and/or molecular• hybrid organic/inorganic
d iti d ll• dye-sensitized cell
Donor acceptor concept Copyrighted Material, from internet
Donor acceptor conceptInterpenetrating Nanostructured Networks
Copyrighted Material, from internet
η record = 4,8%η FMF, ISE = 3,7%
Aluminum
Absorber
Polymer AnodeITO
Substrate
Akzeptor
DonorDonor
The light falls on the polymer El t /h l i t dElectron/hole is generatedThe electron is captured C60
Reducing the cost/watt of delivered solar electricity
The biggest Challenge Copyrighted Material, from internet
Reducing the cost/watt of delivered solar electricityFind a concepts for a more efficient PV systemsMore efficiency, More abundant materials, Non-toxic material, Durability
Fi t G tiFirst GenerationCrystalline Si will remain the dominant PV technology for a long time, the current shortage will be overcome by increased production of pure Siand the introduction of purified metallurgical-grade Si.p g g
Second GenerationThin film modules out of a-Si, CIS, or CdTe have an interesting market opportunity today, their long-term success will depend on efficiency improvements and cost reductionsuccess will depend on efficiency improvements and cost reduction.
Third GenerationTANDEM CELLS: Because sunlight is made up of many colours of different energy, from the high energy ultraviolet to the low energy infrared, a combination of solar cells of different materials can convert sunlight more efficiently than any single cell
Multiple Exciton Generation: The objective is fighting termalization: In quantum dots the rate of energy Multiple Exciton Generation: The objective is fighting termalization: In quantum dots, the rate of energy dissipation is significantly reduced and one photon creates more than one exciton via impact ionization
Higher photocurrent via impact ionization (inverse Auger process)
Thank you so much
Questions or comments?
PVSEC 23th – 27th. 2012 / Rabat - MoroccoProf. Dr. Ahmed Ennaoui
Helmholtz-Zentrum Berlin für Materialien und Energie
Parking: produce electricity and have the shadow
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