Ennaoui cours rabat part III

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

[email protected]

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


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)) .


Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon.

Screen Printer with automatic loading and unloading of cells


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


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?


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


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


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


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


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%


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


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


Module processing

1. KCN etching2. CBD-Buffer


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


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





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


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


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


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 [email protected]

H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol

Fuel Cells

Fuel Cell uses a constant flow of


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


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


Excitonic solar cells

Exciton


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


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

Documents

Ennaoui cours rabat part III