태양전지 및 이차전지 기술 동향청주대 미래창조관

I. 태양전지 개요

II. CIGS 박막 태양전지 구조 및 공정

III. CIGS 박막 태양전지 저가화 및 고효율화

IV. CIGS 박막 태양전지 기술 전망

V. 한국전자통신연구원 연구개발 현황

3

Virtual e-learning System

Flexible Solar CellDigital Actor

Dog-Horse Robot

Flexible Display

Bio-ShirtMIT Device Emotion Robot “Kobie”

Silicon Photonics SAN-based Remote Maintenance Ship Device

4G(LTE, WiBroAdv)Terrestrial DMB

WiBro

Major Achievements

Top of the world in US patents by IPIQ (2012, global 237 research institutes)

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Geothermal

Other REs

Solar heat

Solar Electricity20% 70%

Wind

Biomass adv

Biomass trad

Hydro-PWNuclear PW

GasCoalOil

WBGU: German Advisory Council on Global Change

http://www.wbgu.de/

WBGU’s World Energy Vision 2100

Necessary to develop fundamental technology for Post Grid Parity

Today and Tomorrow of Photovoltaics

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Industry Applications (1/2)

(Grid-connected Domestic Systems)

(Grid-connected Power Plant) (Off-Grid Systems for Rural Electrification)

(Hybrid systems) (Consumer Goods : automobile sun roof) (Off-Grid Industrial Applications)

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Industry Applications (2/2)

power 5.5 W

PV-powered HatPV-powered jacket

유비쿼터스 : 움직이는 동력원(예) 입는 컴퓨터

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Solar Cell Structure and Principle

h e-

Semiconductor materials for PV:

1) Crystalline : Si (Mono, Poly)

2) Compound : CIGS, CdTe, GaAs

3) Organic, Dye-sensitized

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Classification of Solar Cell Materials

Solar Cell Compound

Others

Mono-Si

Si

Thin-film

Wafer-basedPoly-Si

Poly-Si thin-film

Amorphous/microcrystalline thin-film

Group I-III-VI

Group II-VI

Group III-V

CuInSe2, Cu(In,Ga)Se2

CdTe

Cu2S

GaAs

InP

Thin-film

Bulk

Organic, Dye-sensitized, Quantum structure etc.

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Solar Cell Efficiency

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2013년 세계 태양광시장은 설치용량 기준으로 35~40GW에 달할 것으로 예상되며(연초 대비10~20% 상승), 2014년은 42~50GW 정도가 신규로 설치될 전망.

자료 : New Energy Finance , EPIA 한국수출입은행 경제연구소 (‘13)

세계 태양광 시장 추세 및 전망

보수적 전망치 긍정적 전망치

일본, 중국, 미국이 세계 태양광시장을 리드→ 일본은 2013년에 7GW 전후의 규모로 신규 설치될 전망 (작년의 3배를 초과하는 규모)→ 중국은 2013년에 6~9GW를 형성할 전망 (당초 10GW까지 전망했지만 계통연계 여건이 좋지 않음)→ 미국은 2013년에 4~5GW를 신규로 설치할 예정(작년 대비 30% 이상 증가)

PV Market Outlook

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Type a-Si CIGS/CIS CdTe

Technology-Amorphous Si on glass substrate-TFT-LCD mature technology,non-toxic materials

-Cu, In, Ga, Se compound-Price of In materials issue in platpanel display industry

-CdTe compound-Toxic materials and massproduction issue-environmental risk

Efficiency(production)

5～9% 10～13% 7～11%

Efficiency(Laboratory)

> 12% > 19% > 16%

Process Normal Most complicated Relatively simple

Cost Medium Low Low

Environmental risk

Low Medium High

Flexible substrate Easy Difficult Medium

Merits-Mature technology-Easy process-Various substrate

High conversion efficiency Low-cost

Demerits Low conversion efficiency Complicated process Toxic materials (Cd)

IssuesTandem, Triple structure for highefficiency

Scale-up for productionMass production, environmentalrisk

Company Sharp, Mitsubishi, United Solar Nano Solar, Scheuten First Solar, ANTEC Solar

Type of Thin-film Solar Cell

Source: IITA and Credit Suisse 2008.3

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Thin-Film PV Technologies

TechnologyEfficiency

(%)

Relative performance

(Standard Si: 1)Cost

Future relative-cost

Crystalline Si

Non-standard 19.8 1.181.0

→

0.85

Stnadard 17.0 1.00 1.00

Thin-film

a-Si (1-j) 8.0 0.47

0.5

1.06

a-Si/c-Si 9.7 0.57 0.88

CIGS 15.9 0.92 0.55

CdTe 13.2 0.78 0.64

Note) Conversion efficiency of production can be increased to 80% of laboratory efficiencyProduction cost of thin-film: 50 % compared with crystalline

Reference: Bolko von Roedern and Harin S. Ullal (NREL), 33rd IEEE PVSC, 2008

Estimation of PV module cost

Industrial competitiveness of thin-film CIGS technology is the most outstanding

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Solar Cell Efficiency Tables (Version 42)

Prog. Photovolt: Res. Appl. 2013; 21:827-837

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Cell Efficiency (%) Module efficiency (%) M/C

Si (crystalline) 25.0±0.5 22.9±0.6 91.6

Si (multicrystalline) 20.4±0.5 18.5±0.4 90.7

CIGS 19.6±0.6 15.7±0.5 80.1

CdTe 19.6±0.4 16.1±0.5 82.1

a-Si/a-SiGe/nc-Si

(tandem)13.4±0.4 10.5±0.4 78.4

Dye sensitized 11.9±0.4 - N/A

Efficiency: Cell and Module

Prog. Photovolt: Res. Appl. 2013; 21:827-837

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Efficiency and Solar Cell Cost

With higher efficiency modules, thecost per unit area can be much higherfor a given cost target of electricity inkWh. To achieve the proposed targetwith 10% efficient modules requiresthat the modules be less than $10/m2.With modules of 20% efficiency, it isstill possible to meet the proposedtarget with modules that are $75/m2

http://pvcdrom.pveducation.org/main.html

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History of CuInSe2

1953 - CuInSe2 crystals first synthesized by H. Hahn

1974 - First CuInSe2 solar cells from Bell labs, optimized to 12 % efficiency:Wagner et al.

1976 - First thin film CuInSe2/CdS solar cell: L. Kazmierski

1980’s - Advances from Boeing group: >10 % efficiency, elementalevaporation, alloying with Ga

1980’s - Advances from Arco Solar: reaction of metal precursors, thinCdS/ZnO window layers. Module production

1993 - Beneficial role of Na indentified: L. Stolt

1990’s - Advanced absorber fabrication => very high efficiencies: NRELand many others

2000’s - Spurt in investment, many new companies worldwide

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Properties of Cu(InGa)Se2 (1/2)

Chalcopyrite structure: Sphalerite (zincblende) structure with ordered substitution ofGroup I (Cu) and group III (In or Ga)elements

Tetragonal distortion: deviation from c/a=2,changes with Ga/In

Composition fall along tie-line betweenCu2Se and In2Se3

Broad chalcopyrite single phase region ()

Low Cu => -phase: ordered defectcompound (ODC)

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Properties of Cu(InGa)Se2 (2/2)

Demerits◆ Expensive In materials and

production cost still high

◆ Not as efficient as crystalline Si

◆ Complicated process for 4 elements

◆ Standard process equipments issues

Merits◆ Direct band-gap semiconductor; high

efficiency

◆ Wide band-gap engineering: 1.0 ~ 2.7 eV (with Ga, Al, S doping)

◆ High absorption constant; > 105 cm-1 for CIS

◆ Stability & Radiation resistant

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CIGS Structure and Process

Layers Materials Process

Grids Al / Ni E-beam evaporator

(AR coating) MgF2 E-beam evaporator

Window n-ZnO / i-ZnO RF sputtering (MOCVD)

Buffer CdS Chemical bath deposition

Absorber Cu(In,Ga)Se2 (CIGS) Co-evaporationSputtering+Se/S

Backelectrode

Mo DC sputtering

Substrate Soda-lime glass, Stainless Steel foil, Polymer

Cleanig

ZnO250 nm

CdS70 nm

Mo0.5-1 µm

Glass

CIGS1-2.5

µm

Substrate

Mo

CuInGaSe2

CdS

MgF2

Al/Ni contacts

+

-

n-ZnO/i-ZnO

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Isolation(2)

Substrate Back contact Isolation(1) Absorber Buffer

WindowIsolation(3)Attach leads

I-V test LaminationModule

assemblyI-V test

Buffer

Solar module

CIGS Process Flow

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Vacuum compatibilityNot degassing during CIGS deposition

Thermal stabilitywithstand temperatures exceeding 350 C

Suitable thermal expansionComparable coefficient of thermal expansion

Chemical inertnessDuring processing and use

Sufficient humidity barrierAgainst the penetration of water vapor

Surface smoothnessSpike and cavity may lead to shunts

Cost, energy consumption, availability, weightCheap, abundant, lightweight

Requirements for Substrates

F. Kessler, and D. Rudmann, Sol. Energy 77, 685 (2004).

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(Planar magnetron) (Cylindrical magnetron)

New Linear Source for better uniformity

Elemental co-evaporationSimultaneous delivery of Cu, In, Ga, Se to a hot substrate.

Produces the highest efficiency devices

Control of film composition, gradient

Manufacturing: pioneering work by Boeing in 1980’sIn-line process in development or production by several companies

Large area module > 13%

Precursor reaction – two-step processes:Cu + In + Ga + (Se) Cu(InGa)(SeS)2

First – deposition of precursor film

Second – reaction with Se/S

Potential for lower cost – uniform, high materials utilization

Cell performance: less reported, comparable with wide Eg

Manufacturing: pioneering work by Arco Solar in 1980’sBatch, RTP process in development or production by several companies.

Large area module > 13%

CIGS Deposition

Se, S

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Cu(InGa)Se2 Co-evaporation

◆ Elemental Cu, In, Ga, Se vapor onto heated substrate

◆ Independent control of each element:

▷ Co-evaporation Ga / (In + Ga) gradient Energy band-gap gradient

▷ Cu-rich thin film growth

PBase 110-6 torrPRun 210-5 torr

To Vac. Pump

Substrate Heater (~550C)

Thickness Monitor

Thermal Evaporation Sources for

Cu, In, Ga, Se, (S)

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In-line Evaporation

◆ Translation of heated substrate over of

sequential array of sources

◆ Can be implemented with glass substrate or

roll-to-roll flexible substrate

▷ Roll-to-roll process high throughput

▷ Reproducibility

▷ Scalable to wide areas

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Precursor Reaction: 2-step Process

◆ Cu, In, Ga precursors

▷ Selection: low cost, uniformity, efficient material use Sputtering – commercial equipment available Ink printing – maximizing material use, non-vacuum Electro-deposition – frequent batch process

◆ Hydride gas (H2Se, H2S) or elemental atomic vapor (Se, S)

▷ Batch or in-line▷ Rapid Thermal Process (RTP)

◆ Multi-step process for Cu(InGa)Se2 phase formation

Mo/Cu/Ga/InH2Se/H2S,

Se/S reaction

400 – 600C

Mo/Cu(InGa)Se2

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CIGS Structure: Rigid vs. Flexible

Flexible substrate

Insulator

Back elctrode

Absorber

Buffer

Window

Impurities

Grids

Grids

Substrate

Mo

CuInGaSe2

CdS

MgF2

Al/Ni contacts

+

-

n-ZnO/i-ZnO

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Helios Flying by AeroVironment Inc.

Highly flexibleVarious shapes and sizes

Customized and integratedVarious lengths and widths

Thin and lightweightLightness and aesthetic integration

UnbreakableTough, durable and safe to use

Environmentally friendlyShorter energy payback time

Advantages of Flexible Solar Devices

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CIGS PV Modules: Status

Nominal output(W)

Open circuit voltage (V)

Short circuit current (A)

Dimension (mm)Weight

(kg)Specific

Power (W/kg)

Module (M사) 111 24.9 6.80 665 x 1611 x 28 18.0 6.17

Module (S사) 165 110 2.20 977 x 1257 x 35 20.0 8.25

Module (G사) 62 28 4.2368 x 216 x 36 (fold)

1333 x 762 x 2.5 (deployed)1.41 43.97

Module (S사) 115 24.1 7.61 800 x 1320 x 11.5 1.40 82.14

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Properties of Materials

Steel category

Steel grade Chemical composition (%) Physical properties

KS (JIS) C Cr Ni MoSpecific heat

J/gC

Modulus of elasticity

×10³N/mm2

Coefficient of thermal expansion

×10-6/C(20-100℃)

Thermalconductivity×10W/mC(20-100℃)

Austenitic 316 ≤ 0.08 16.0-18.0 10.00-14.0 2.00-3.00 0.50 194 16.0 16.3

Ferritic 430 ≤ 0.12 16.0-18.0 0.46 200 10.4 26.4

F. Kessler, and D. Rudmann, Sol. Energy 77, 685 (2004).

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2~3 m-thick SiO2, SiOx, SiOx:Na, Al2O3, ZnO

Radio frequency sputtering, plasma enhanced chemical vapor deposition, orsol–gel deposition

Adhesion properties and mechanical stability

Dielectric Layer for Diffusion Barriers

F. K. D. Herrmann et al., Mater. Res. Soc. Symp. Proc., San Francisco, USA, 763, pp. 287–292(2003).

C. Y. Shi et al., Sol. Energy Mater. Sol. Cells 93, 654 (2009).

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Enhanced performancein amounts of typically about 0.1 at.%

better film morphology, passivation of grain-boundaries

higher p-type conductivity, reduced defect concentration

Supply methodsIn case SLG substrates, incorporated into CIGS during growth by diffusion

Na or Na compound (for examples, NaF, Na2S or Na2Se) prior to or during back contactdeposition, onto the back contact prior to CIGS growth, co-evaporation during CIGSdeposition, and Na in-diffusion into as-grown absorbers.

Na Incorporation

D. Rudmann, in Department of Physics (Swiss Federal Institute of Technology, Zurich, 2004).

Na or Na compound

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CIGS Efficiencies with Various Substrates

S. Niki et al., Prog. Photovolt: Res. Appl. 18, 453 (2010).

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Flexible CIGS PV: Roll-to-roll

(1) Co-Evaporation in Vacuum

(2) Physical Vapor Deposition + Selenization

(3) Non-vacuum Deposition + Selenization

(1)

(2)

(3)

Source: J. S. Britt (Global Solar Energy Inc.), PVSC2008

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Roll-to-roll Manufacturing

(FHR’S roll-to-roll System)

( Fraunhofer’s Roll to Roll System concept)

(Ascent Solar’s roll-to-roll system)

(Miasole’s roll-to-roll system)

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Fabrication of Modules

Tempered glass as cover glass

Al frame

CIGS-based circuit

Junction box with leads

Soda-lime glass as substrate

EVA

EVA/Tedler

Sealant

Surface protective film

Flexible solar cell submodule

Connective lead

Transparent bond

Surface protective film

Lead wire

Y. Hamakawa, Thin-Film Solar Cells: Next Generation Photovoltaics and Its Applications (Springer, Heidelberg, 2004).

cover glass

laminating

cells

laminating

plastic backing

junction boxaluminum

frame

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Monolithic Integration in Flexible Module

(a) rigid substrate (SLG)

(b) flexible substrate (Polyimide)

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Barrier requirements for different applications.

Flexible Packages

Florian Schwager, Elements 31 (2010).

Requirements on water vapor and oxygen transferof barrier films for solar cells are particularly high.

C. Charton et al., Thin Solid Films 502, 99 (2006).

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Tandem Cell Structure

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High performance photovoltaic project,

National Renewable Energy Laboratory(2001)

Monolithic Tandem

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Mechanically Stacked

41

CdTe/CIGS Tandem

42

DSSC/CIGS Tandem

S. Wenger et al., Appl. Phys. Lett., 94 (2009) 173508.

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Future Challenges and OpportunitiesDevice structure varies between monolithically & mechanically integrated modules

Today Forward

ZnO, ITO (2500 Å)• Sputter

Hardened TCO (moisture barrier)

CdS (700 Å)• Chemical Bath Depo

sition • Sputter

Cd-free; dry, eliminate

CIGS (1-2.5 µm)• Multiple methods

(coevaporation,sputtering,

printing,electrodeposition)

Increase Ga-%,Reduce thickness, Rapid deposition

Uniformity (composition, temp., thickness)

Mo (0.5-1 µm)• Sputter

Na dosing

Glass,Metal Foil,

Plastics

High temp. glassMetal foils: smooth,

flex-dielectric (monolith.)

• Screen Print Ag • Reduce shadowing• Faster application

Front Contact Grid

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Module costs must be considered in the context of module efficiency (impact oninstallation costs)

CIGS Manufacturing Costs

Courtesy of NREL (2011)

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Layer Stacks and Module Process

LayersProcess / materials

Avancis Solar frontier Sulfurcell Wuerth solarAscent,Solarion

Global solar

N-type TCO (1 m) + i-ZnO

RF-sputter,MOCVD

ZnO:Al ZnO:B ZnO:Al ZnO:Al ZnO:Al / ITO ZnO:Al

Buffer (50-100 nm)

CBD,ALD, ILGAR

CdS Zn(S,OH) CdS CdS CdS CdS

Absorber (1.5-2.5 m)

Evaporation, sputter-reaction

Cu(In,Ga)(S,Se)2

Cu(In,Ga)Se2, Cu(In,Ga)

(S,Se)2

CuInS2 Cu(In,Ga)Se2 Cu(In,Ga)Se2 Cu(In,Ga)Se2

Back contact (0.5-1.0 m)

DC-sputter Mo+barrier Mo+barrier Mo Mo Mo Mo+barrier

Substrate Rigid, flexible Window glass Window glass Window glass Window glass PolyimideStainless steel

foil

Absorber growthTechnology

-Sputter-

RTASputter-Furnace

Sputter-Furnace

Evaporation Evaporation Evaporation

rigid flexible

S. Niki, M. Contreras, I. Repins, M. Powalla, K. Kushiya, S. Ishizuka, and K. Matsubara, Prog. Photovolt: Res. Appl. 18, 453 (2010).

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