2014년 제1회 태양광기술 지식연구회 - Cu(In,Ga)Se2 박막 태양전지 기술 동향 및 이슈 -

태양전지 및 이차전지 기술 동향 청주대 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 Cell Digital Actor

Dog-Horse Robot

Flexible Display

Bio-Shirt

MIT Device Emotion Robot “Kobie”

Silicon Photonics SAN-based Remote Maintenance Ship Device 4G

(LTE, WiBro Adv)

Terrestrial DMB

WiBro

Major Achievements

Top of the world in US patents by IPIQ

(2012, global 237 research institutes)

Geothermal Other REs Solar heat

Solar

Electricity

http://www.wbgu.de/

WBGU’s World Energy Vision 2100

Necessary to develop fundamental technology for Post Grid Parity

5

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) 6

Industry Applications (2/2)

유비쿼터스 : 움직이는 동력원

(예) 입는 컴퓨터

7

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

Classification of Solar Cell Materials

Solar Cell

Compound

Others

Mono-Si

Si

Thin-film

Wafer-based

Poly-Si

Poly-Si thin-film

Amorphous/microcrystalline

thin-film

Group I-III-VI

Group II-VI

Group III-V

CuInSe

, Cu(In,Ga)Se

CdTe

Cu

S

GaAs

InP

Thin-film

Bulk

9

Solar Cell Efficiency

10

2013년 세계 태양광시장은 설치용량 기준으로 35~40GW에 달할 것으로 예상되며(연초 대비

10~20% 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

11

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 plat panel display industry

-CdTe compound

-Toxic materials and mass production 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)

Issues Tandem, Triple structure for high_efficiency Scale-up for production Mass production, environmental_risk

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

Thin-Film PV Technologies

Technology

Efficiency

_(%)

performance

Relative

(Standard Si: 1)

Cost

Future

relative-cost

Crystalline

Si

Non-standard

19.8

1.18

1.0

→

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 efficiency

Production 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

13

Solar Cell Efficiency Tables (Version 42)

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

14

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

15

Efficiency and Solar Cell Cost

With higher efficiency modules, the

cost per unit area can be much higher

for a given cost target of electricity in

kWh. To achieve the proposed target

with 10% efficient modules requires

that the modules be less than $10/m

_.

With modules of 20% efficiency, it is

still possible to meet the proposed

target with modules that are $75/m

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

History of CuInSe

₂

1953 - CuInSe

₂

crystals first synthesized by H. Hahn

1974 - First CuInSe

₂

solar cells from Bell labs, optimized to 12 % efficiency:

Wagner et al.

1976 - First thin film CuInSe

₂

/CdS solar cell: L. Kazmierski

1980’s - Advances from Boeing group: >10 % efficiency, elemental

evaporation, alloying with Ga

1980’s - Advances from Arco Solar: reaction of metal precursors, thin

CdS/ZnO window layers. Module production

1993 - Beneficial role of Na indentified: L. Stolt

1990’s - Advanced absorber fabrication => very high efficiencies: NREL

and many others

17

Properties of Cu(InGa)Se

₂

(1/2)

Chalcopyrite

structure:

Sphalerite

(zinc

blende) structure with ordered substitution of

Group 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 between

Cu

₂

Se and In

₂

Se

₃

Broad chalcopyrite single phase region ()

Low

Cu

=>

-phase: ordered defect

compound (ODC)

18

Properties of Cu(InGa)Se

₂

(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;

 > 10

_cm

_{for CIS}

19

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-evaporation

Sputtering+Se/S Back

electrode Mo DC sputtering

Substrate Soda-lime glass, Stainless _{Steel foil, Polymer} Cleanig

ZnO 250 nm CdS 70 nm Mo 0.5-1 µm Glass CIGS 1-2.5 µm

Substrate

Mo

CuInGaSe

CdS

MgF

Al/Ni contacts

+

-n-ZnO/i-ZnO

Isolation(2)

Substrate

Back contact

Isolation(1)

Absorber

Buffer

Window

Isolation(3)

Attach leads

I-V test

Lamination

Module

assembly

I-V test

Buffer

Solar module

21

Vacuum compatibility

Not degassing during CIGS deposition

Thermal stability

withstand temperatures exceeding 350

C

Suitable thermal expansion

Comparable coefficient of thermal expansion

Chemical inertness

During processing and use

Sufficient humidity barrier

Against the penetration of water vapor

Surface smoothness

Spike and cavity may lead to shunts

Cost, energy consumption, availability, weight

Cheap, abundant, lightweight

Requirements for Substrates

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

22 (Planar magnetron) (Cylindrical magnetron)

New Linear Source for better uniformity

Elemental co-evaporation

Simultaneous 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’s

In-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)

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 E

Manufacturing: pioneering work by Arco Solar in 1980’s

Batch, RTP process in development or production by several companies.

Large area module > 13%

CIGS Deposition

23

Cu(InGa)Se

₂

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

P

 110

_torr

P

 210

_torr

To Vac. Pump

Substrate Heater (~550C)

Thickness Monitor

Thermal Evaporation

Sources for

Cu, In, Ga, Se, (S)

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

25

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 (H

Se, H

S) or elemental atomic vapor (Se, S)

▷

Batch or in-line

▷

Rapid Thermal Process (RTP)

◆

Multi-step process for Cu(InGa)Se

phase formation

Mo/Cu/Ga/In

_H

Se/H

S,

Se/S reaction

400 – 600C

Mo/Cu(InGa)Se

CIGS Structure: Rigid vs. Flexible

Flexible substrate Insulator Back elctrode Absorber Buffer Window Impurities Grids Grids

Substrate

Mo

CuInGaSe

CdS

MgF

Al/Ni contacts

+

-n-ZnO/i-ZnO

27 Helios Flying by AeroVironment Inc.

Highly flexible

Various shapes and sizes

Customized and integrated

Various lengths and widths

Thin and lightweight

Lightness and aesthetic integration

Unbreakable

Tough, durable and safe to use

Environmentally friendly

Shorter energy payback time

Advantages of Flexible Solar Devices

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 4.2 368 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

29

Properties of Materials

Steel category

Steel grade Chemical composition (%) Physical properties

KS (JIS) C Cr Ni Mo Specific heat_J/gC Modulus of elasticity ×10³N/mm2 Coefficient of thermal expansion ×10-6_/C (20-100℃) Thermal conductivity ×10W/mC (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).

30

2~3

m-thick SiO

₂

, SiO

_x

, SiO

_x

:Na, Al

₂

O

₃

, ZnO

Radio frequency sputtering, plasma enhanced chemical vapor deposition, or

sol–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).

31

Enhanced performance

in amounts of typically about 0.1 at.%

better film morphology, passivation of grain-boundaries

higher p-type conductivity, reduced defect concentration

Supply methods

In case SLG substrates, incorporated into CIGS during growth by diffusion

Na or Na compound (for examples, NaF, Na

S or Na

Se) prior to or during back contact

deposition, onto the back contact prior to CIGS growth, co-evaporation during CIGS

deposition, 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

33

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

34

Roll-to-roll Manufacturing

(FHR’S roll-to-roll System)

( Fraunhofer’s Roll to Roll System concept)

(Ascent Solar’s roll-to-roll system)

35

Fabrication of Modules

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 box aluminum frame

Monolithic Integration in Flexible Module

(a) rigid substrate (SLG)

37

Barrier requirements for different applications.

Flexible Packages

Florian Schwager, Elements 31 (2010).

Requirements on water vapor and oxygen transfer

of barrier films for solar cells are particularly high.

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

38

39

High performance photovoltaic project,

National Renewable Energy Laboratory(2001)

Monolithic Tandem

41

CdTe/CIGS Tandem

42

DSSC/CIGS Tandem

43

Future Challenges and Opportunities

Device structure varies between monolithically & mechanically integrated modules

Today

Forward

ZnO, ITO (2500 Å)

Hardened TCO

(moisture barrier)

CdS (700 Å)

• Chemical Bath Depo sition • Sputter

Cd-free; dry, eliminate

CIGS (1-2.5 µm)

Increase Ga-%,

Reduce thickness,

Rapid deposition

Uniformity

(composition, temp., thickness)

Mo (0.5-1 µm)

• Sputter

Na dosing

Glass,

Metal Foil,

Plastics

High temp. glass

Metal foils: smooth,

flex-dielectric (monolith.)

• Screen Print Ag _{• Reduce shadowing}

• Faster application

Front Contact Grid

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

installation costs)

45

Layer Stacks and Module Process

Layers Process /

materials Avancis Solar frontier Sulfurcell Wuerth solar

Ascent,

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) sputter-reactionEvaporation, 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 Polyimide Stainless steel foil Absorber growth Technology - Sputter-RTA Sputter-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).