tco 박막의태양전지응용 -...

2010. 5. 13

공과대학 신소재공학부

이희영 교수

TCO 박막의 태양전지 응용

http://www.yeungnam.ac.kr/main.php

Outline

- TCO 란무엇인가?

- TCO 의종류

- TCO 박막의응용분야

- TCO 박막의태양전지응용


TCO

- Transparent Conductive Oxide의줄임말

- 가시광선대역에서의높은투과율(비금속절연체의특징)

+

- 낮은전기저항 (금속도체의특징)

☞ 일부금속산화물(세라믹)에서위의두가지특성이동시에만족되는것이발견됨!


Properties (and Parameters) of Interest

TCO

Physical, Chemical & Thermal Durability

Etchability Conductivity

Plasma Wavelength

(or frequency)

Bandgap Thickness

Deposition Temperature

Uniformity, Toxicity, Cost, …


General Requirement for TCO Thin Films

- Low Resistivity (ρ ≤ 10-3 Ωcm)

- Optical Transparency ≥ 80%

- Optical Bandgap ≥ 3.5 eV

- Processing Considerations : Deposition/Etching

- Low Material Cost

- Low Pollution/Toxicity


Optical Properties

Transmission window : 400nm

Table. Approximate Minimum Resistivities and Plasma Wavelength For Some Transparent Conductors.

Physical Parameters


Outline


- TCO 의종류




Five closely grouped d10 cations

Zn2+, Cd2+, In3+, Ga3+, Sn4+

Simple oxides

ZnO, CdO, In2O3, SnO2 → TCOs

Ga2O3 → wide bandgap insulator

Combination of the above

10 binary, 10 ternary, 5 quaternary, 1 quintinary

→ total of 26 combinations

ZnO

In2O3

Ga2O3

CdO

SnO2

n-Type TCO


Electronic Properties of TCO Materials

(Source : T. Minami, MRS Bulletin, August, 2000)


In3+(3/4, face diagonal)

In3+(1/4, body diagonal)

O2-(1/4, removed)

- formed by removing one-fourth of the anions from the Fluorite

structure and allowing for small shifts of the ions

Crystal Structure of ITO - Bixbyite

In

O

Oxygen Vacancy

(Lattice constant of cubic In2O3 = 10.117 Å . Unit cell has 80 atoms.)


ITO System

In2O3 20 40 50 60 70 80 90 SnO2

mol% In2O3

2000

1800

1600

1400

1200

1000

800

InO1.5 20 40 60 80 SnO2xSn (%)

Tem

per

atu

re (

K)

C1+C2 C2+T

C1+T

C1 T

C1: Cubic In2O3

C2: In4Sn3O12

T: rutile

C2

Sn Solubility limit = 6.6~8.1 at%

In3+

Oxygen vacancy

Oxygen

Sn4+

(100) plane in cubic bixbyite structure.


ITO System

OInOSnSnOIn iInXX

In 322 )2(22"

OOIne'SnSnOIn gInX

In )(2322 2

12222

Oe'SnOSn gIniIn"

)(22

1222

e'VOO"Og

X

O 2)(221

Donor Generation

Self-Compensation

(Source : T. Minami, MRS Bulletin, August, 2000)


Properties of Indium Tin Oxide (ITO)

- SnO2 doped In2O3 : 5~10%

- Deposited by DC Magnetron Sputtering

- ρ ≈ 10-4 Ωcm

(RS ≤ 10 Ω/□ at 150 nm thickness)

- Optical Transparency ≥ 85%

Eg = 3.6~3.7 eV

- Low Temp Processing/Easy Patterning


Price of Indium Soars!

200

400

600

800

($/kg)

1,000

5260 56

310

1200

100

800

600

1,200

220200

We need inexpensive alternatives!


IZO System - In2O3(ZnO)k compound

(k+1)In1/k+1Znk/k+1O1/(k+1)+ layers

(In/ZnO) Würtzite structure

InO2- layer

Bixbyite st.

c-axisZn or In

In

O

c

c

h

h

h

h

h

h

c

c

distorted octahedral

tetrahedral

trigonal-bipyramidal

InO2- layer


IZO System

Fig. Variation of the conductivity (σ) (●),the carrier concentration

(n) (▲ )and the mobility (μ) (◆ ) as a function of Zn/(Zn+In) (at.)ratio and the structure evolution.

k=2 k=3

0.0 0.2 0.4 0.6 1.00.8

In2O3+Zn5In2O8

In2O3+Zn4In2O7

In2O3+Zn3In2O6

k in ZnkIn2Ok+31 2 3 4 5 6 7 9

1311 15

Zn7In2O10+ZnO

Zn9In2O12+ZnO

Zn13In2O16+ZnO

Zn

11In

2O

14+

Zn

OZ

n15In

2O

18

+Z

nO

Zn

5In

2O

8+

Zn

7In

2O

10

1200

1100

1300

1400

InO1.5

[Zn]/([Zn]+[In])

ZnO

nine homologous compounds!


Summary of electrical properties of TCO thin films

Sample

Process T (oC)

Deposition/An

nealing

Electrical

Resistivity

(Ωcm)

Electron

Concentration

(cm-3)

Hall Mobility

(cm2 V-1 sec-1)

ITO-as 25/no ~1.2 × 10-3 2.5 × 1020 20

ITO-300-FGA 25/300 ~3 × 10-4 1 × 1021 20

IZTO-as 25/no ~1.0 × 10-3 1.6 × 1020 40

IZTO-300-FGA 25/300 ~5.5 × 10-4 ~3 × 1020 40


ZnO-Based System

O2- : HCP

Zn2+ : ½ tetrahedral site

- Eg ~ 3.2 eV

- Resistivity : 10-4 ~10-3 Ωcm


SnO2-Based System

- Eg ~ 3.7 eV

- Resistivity : 10-3 ~ 10-2 Ωcm

- Wet etching is very difficult!

- F- or Sb- doped films

(FTO, ATO)


Optical Transmission Spectra

Annealed at 550℃in low vacuum for 30 min

200 300 400 500 600 700 800

0

20

40

60

80

100

TO

Sb 2 mol %

Sb 4 mol %

Sb 5 mol %

Sb 6 mol %

Sb 8 mol %

Sb 10 mol %

Tra

nsm

itta

nce (

%)

Wavelength (nm)

Annealed at 550℃ for 30 minat various atmospheres

Sb 5 mol % doped, t = 2000ÅVarious Sb doping level, t = 2000Å

200 300 400 500 600 700 800

0

20

40

60

80

100

O2

low vacuum

high vacuum

10% H2 - 90% Ar

Tra

nsm

itta

nce (

%)

Wavelength(nm)

*

*

*

*


Electrical Parameters of ATO Thin Films

Modified Sol-Gel or Metalorganic Decomposition (MOD)

5~8 mol % Sb-Doping

⇒Resisitivity

: 8 ~ 10 × 10-3 Ωcm

⇒Transmittance

: about 80 ~ 90 %


투명전극특성 다양화

새로운 응용

분야도출

태양 전지의 p형 투명전극

투명소자에서의 p형 전극

투명 광전자 소자의 핵심기술

UV-LED, UV-Detector

각종 투명전자소자

p-type TCO


The crystal structure of delafossite, AMO2. The layers of A and MO2 are stacked alternately along the c-axis.

p-type TCO: Crystal Structure


p-type TCO: Properties

Table. Preparation conditions of thin films of CuAlO2, CuGaO2,

and SrCu2O2 by pulsed laser deposition.

CuAlO2(CAO) , CuGaO2(CGO)


Structure of transparent thin film diode. SrCu2O2 and ZnO used as p- and n-type semiconductor materials, respectively. ITO and n+-ZnO are the “metallic” electrodes to the semiconductor layers.

p-type TCO: Application


Thin Film Deposition Process


Outline


- TCO 의종류




Applications of TCO Thin Films

Optoelectronic Devices

Heated Mirror

Touch Panel/Screen

Solar Cell

Transparent

Conducing

Oxide

Thin film Resistor

Gas Sensor

Flat Panel Displays

Smart Window


Flat Panel Displays – PDP, LCD, OLED

Counter Electrode(ITO)

TFT

BM

Polarizer

Pixel Electrode(ITO)

LC Electric

Field

Polarizer

UP

BPDisplay Electrode

(Transparent)

Dielectric

Layer

MgO

Layer

Barrier Lib

(Separator)

Phosphor

Address electrode

Xe-Ne discharge

Rear Glass Plate

Front Glass Plate

Gas Discharge mechanism

by gas mixture

(He or Ne + Xe 3~10 %)

Phosphor(R,G,B) : Fluorescence

Visible Light

Excitation by UV light

Zn2SiO4:Mn for Green

Y2O3 : Eu for Red

BaMgAl14O23:Eu for Blue

Light

Glass Substrate

Anode (ITO, IZO)

HIL / HTL

EML

EIL / ETL

Cathode (Al)


barrier film / ITO / buffer layer / OLED layer / Cathode / barrier film

Prototype Spec.

- Discrete RGB Pixels - Thickness: 0.25mm

- Film size: 150mm150mm - Active area: 110mm90mm

(Source : Dai Nippon Printing)

Flat Panel Displays – Flexible Display


Window

ITO

Pd

Mg-Ni alloy film

Electrolyticsolution

Seal

gla

ss gla

ss

Mirror

Structure of smart window

Smart Window

(Source : NREL)


Smart Window

(Source : Azens and Granqvist, J.SolidSt.Electrochem., 7, 2003)


Solar Cell

(Source : K.L. Chopra et al., Prog. Photovolt. Res. Appl., Vol. 12, 69, 2004)


Transparent Electronics

(Sources: J.F. Wagner, Science, Vol. 300, 1245, 2003. K. Nomura et al., Nature, Vol. 432, 488, 2004.)


Transparent Electronics

(Source: K. Nomura et al., Science, Vol. 300, 1269, 2003.)


Transparent Display in Action – “Minority Report”

All-oxide transparent electronics


Transparent Display in Action – “A Life in Japan”

(Source: http://lucid.msl.titech.ac.jp/~www/TopPage-e.html)


Outline


- TCO 의종류




“PV Power Plant” “BIPV”

(Source: S.J. Moon, WGEF, 2008)


태양전지에 사용되는 TCO의 종류

FTO

(김동호 외, 박막형 태양전지 소재기술, 기계와 재료, 21권 2호, 2009년 7월)


Crystalline vs Thin Film Solar Cells


비정질 실리콘 박막 태양전지

(http://www.agc.co.jp/english/csr/environment/products/positive_seihin1.html)



단일접합 a-Si:H 박막 태양전지 구조 : (a) pin superstrate 형, (b) nip substrate 형

이정철, 윤경훈, 박막 실리콘 태양잔지 기술동향, 세라미스트, 2005년 10월)



이정철, 윤경훈, 박막 실리콘 태양잔지 기술동향, 세라미스트, 2005년 10월)

pin a-Si:H 박막 태양전지 band diagram; (a) ideal, (b) realistic, (c) light-soaked solar cells


태양전지 재료의 광흡수계수

이론 효율 ~25%


(김제하, 화합물반도체 박막태양광발전 기술과 산업동향, IT SoC Magazine 2009년 11월호)

i-ZnO/Al:ZnO

CdS (50nm)

Cu(In,Ga)Se2

Mo

Glass, SUS, PI

CIGS 태양전지의 구조


ZnO, ITO

2500 Å

CdS

700 Å

Mo

0.5-1 µm

Glass,

Metal Foil,

Plastics

CIGS

1-2.5 µm



(김제하, 화합물반도체 박막태양광발전 기술과 산업동향, IT SoC Magazine 2009년 11월호)

CIGS 태양전지의 흡수층 제조공정


ZnO Thin Film SnO2 (Asahi)

(http://www.products.cvdequipment.com/applications/tcocoating/3/)

표면 texturing 구조를 갖는 투명전도막

LPCVD 또는 MOCVD 공정 스퍼터링 + Texturing 공정



(http://www.optoiq.com/index/display/article-display/363243/articles/laser-focus-world/features/photovoltaics-short-wave-infrared-cameras-characterize-thin-film-solar-cells.html)


염료감응형 태양전지(DSSC)

(Source: Wikipedia)

http://www.yeungnam.ac.kr/main.phphttp://en.wikipedia.org/wiki/File:Dye_Sensitized_Solar_Cell_Scheme.pnghttp://en.wikipedia.org/wiki/File:Dye.sensitized.solar.cells.jpg

유기태양전지(OPV)

IZTO work function mayvary widely depending onthe composition.


Thank You for Your Attention!

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