Investigation of pulsed D C magnetron sputtering for the component layers of CuInSe2 baseed solar cells

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Investigation of pulsed D.C magnetron

sputtering for the component layers of

CuInSe2 baseed solar cells

Karthikeyan, Sreejith, Hill, AE and Pilkington, RD

Title Investigation of pulsed D.C magnetron sputtering for the component layers of CuInSe2 baseed solar cells

Authors Karthikeyan, Sreejith, Hill, AE and Pilkington, RD

Type Conference or Workshop Item

URL This version is available at: http://usir.salford.ac.uk/19232/ Published Date 2011

USIR is a digital collection of the research output of the University of Salford. Where copyright permits, full text material held in the repository is made freely available online and can be read, downloaded and copied for noncommercial private study or research purposes. Please check the manuscript for any further copyright restrictions.

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CMMP 11

Investigation of pulsed D C magnetron sputtering for the

CMMP 11

Investigation of pulsed D.C magnetron sputtering for the

component layers of CuInSe

₂

based solar cells

S jith K thik A th Hill d Ri h d Pilki t

Materials and Physics Research Centre University of Salford, UK

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Introduction

CIS/CIGS thin film based solar cells are the most promising renewable energy source because of their relatively high solar efficiency and stability

because of their relatively high solar efficiency and stability.

Single crystal Si cells need more material to absorb light due to its indirect band gap.

In CIS the defect mechanisms makes it a direct semiconducting materials and no doping is needed

needed.

Presently CIGS cells have achieved a maximum efficiency of 20.3% [1]. A typical cell CIS/CIGS structure is in the form of a heterojunction.yp j

CdS~ 50nm

i-ZnO~ 70nm

ZnO ~ 1?m

CdS~ 50nm

i-ZnO~ 70nm

Al-ZnO ~ 1µm

N- type buffer layer

Intrinsic ZnO layer to reduce leakage current Transparent Conductive Oxide layer

Substrate Mo layer ~ 0.8? m

CuInSe2~ 1.0? m

CdS 50nm

Substrate

Mo layer ~ 0.8

CdS 50nm

µm

CuInSe2~ 2µm

N type buffer layer P- type absorber layer

Back Contact

1

References

[1] P. Jackson et. al Progress in Photovoltaics: Research and Applications, (2011) EU PVSEC WCPEC-5, Valencia, Spain, 2010. Substrate

Substrate

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The first published report of a CuInSe₂ thin film was by the R.D Tomlinson group at the University of Salford in 1974 [2]

Introduction

the University of Salford in 1974 [2].

Films of CIS are generally made by multi-step processes

My work has been focussed on a SINGLE STEP process which can deposit films ith

with.

9 Nearly stoichiometric ratio.

9 p-type characteristics.

9 No secondary phases.

9 No additional substrate heating for crystallisation.

9 Less material wastage.

9 No carbon, oxygen, chlorine etc. contamination.

This work reports such a single step deposition process for nearly stoichiometric p-type CIS layers and also for the other component layers of a cell using Pulsed D.C Magnetron

No carbon, oxygen, chlorine etc. contamination.

y p y g g

Sputtering (PDMS) from powder targets.

2

References

(5)

Materials Deposited

1 Molybdenum (back contact)

1. Molybdenum (back contact)

2. Copper indium diselenide (absorber layer)

3. Indium sulphide (buffer layer)

4. Indium oxide (Transparent Conductive Oxide layer)

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Sputtered in argon atmosphere from commercial Mo powder.

Films sputtered at different substrate temperatures

Molybdenum Films

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XRD of Mo Films

Deposition Parameters

Pressure : 7.0x10-3_mbar

Mode : Constant Power (50W) Frequency : 75 kHz

M l 205 0

(110)

Frequency : 75 kHz Pulse off Time : 0.5 µs Distance : 10 cm

Body-centred cubic phase

Molp205

Molp204

300 0C

250 0C

ty

(arb.u

nit)

Body-centred cubic phase

With increase in

substrate temperature Molp203

Molp202

M l 201

200 0C

0

150 0C

In

ten

si

t

A shift in 2θ towards higher angles was noticed.

15 20 25 30 35 40 45 50 55 60 65

Molp201 Molp200

100 0C 47 0C

2θ (degrees)

5

2θ (degrees)

S. Karthikeyan et al, Nano-structured features of pulsed d.c magnetron sputtered Mo films for photovoltaic application Thin Solid Films, 2011, accepted for publication.

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Strain Analysis of Mo Films

40 2 40.4

3

40.0 40.2

2

θ

2 St

ra

i

39.6 39.8

2

1

n %

0 50 100 150 200 250 300 39.4

T t

0

Temperature

Strain % reduced with increase in temperature

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2.2x10-3

Resistivity Analysis of Mo Films

1.6x10-3 1.8x10-3

2.0x10-3 Resistivity

1.0x10-3 1.2x10-3 1.4x10-3

ivity (

Ω

cm

)

4 0x10-4 6.0x10-4 8.0x10-4

Resi

st

i

50 100 150 200 250 300

2.0x10-4 4.0x10

Temperature (p (0C))

Resistivity reduced with increase in temperature

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SEM and AFM Studies of Mo Films

No heating

SEM AFM

g

Morphological

200 nm

p g

change from a

cluster of small grains to a fibrous, columnar needle like 400 nm

150 0_C columnar needle-like

structure for films grown at 150 0_C

200 nm

8 Al-Thani, H.A et al, 2002,Twenty-Ninth IEEE Photovoltaic Specialist Conference,pp 720-3 .

References

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S tt d i t h Sputtered in argon atmosphere from our CuInSe₂ powder.

Films sputtered from CIS powder s sputte ed o C S po de with different compositions

C

I di

Di l

id Fil

Copper Indium Diselenide Films

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CuInSe

₂

Crystal Growth

Selenium, Indium and Copper

inside quartz tube before sealing CuInSe2inside ampoule after direct fusion

CuInSe₂polycrystalline ingots CuInSe2powder

10

References

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XRD of CuInSe

₂

Films

12)

Pressure : 7.5x10-3_mbar

Mode : Constant Current (0.12A Frequency : 130 kHz

Pulse off Time : 1.0 µs Distance : 10 cm

CIST116 (220/ (301)

204)

(1

(116/

312)

5 % extra In

CIST115 CIST114 CIST113 s ity (arb . un it)

5 % extra Se

(21.54:24.29:54.17) (20.53:27.97:51.50)

CIST111 CIST112 In te n s

Nearly stoichiometric powder (23.03:23.32:53.66)

( )

Preferred (112) orientation

Single Phase

10 20 30 40 50 60

CIST104 CIST105

In rich powder (19.95 : 34 .10 : 45.95 )

g

No heating !!

10 20 30 40 50 60

2θ

11

Reference

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Ternary Diagram of CuInSe

₂

Films and Powder

45 50 40 45 45 50 40

45 Stoichiometric Point

In % 30 35 45 Se % 50 55 60 65 40 In % 30 35 45 Se % 50 55 60 65

40 Starting Powder Composition Film Composition 10 15 20 25 65 70 75 80 10 15 20 25 65 70 75 80 30 0 32.5 47.5 50.0 30 0 32.5 47.5 50.0 Cu %

10 15 20 25 30 35 40 45 50 10

Cu %

10 15 20 25 30 35 40 45 50 10

In %

25 0 27.5 30.0

Se % 52.5

55.0 25 0 27.5 30.0 52.5 55.0 Ternary Diagram 20.0 22.5 25.0 57.5 60.0 20.0 22.5 25.0 57.5 60.0 y g

All films were p-type

Cu %

20.0 22.5 25.0 27.5 30.0 32.5

12

References

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Optical Studies of CuInSe

₂

Films

2 4

2 2

1 (1 ) ((1 )

.ln

2. 4.

R R

R

d T T

α = − ⎛⎜_⎜ − + − + ⎞⎟_⎟

⎝ ⎠ 0.7 0.8 0.9 1.0 ctran ce Transmittance Reflectance _1.00E+013 1.004 eV CIS 3Hr ⎝ ⎠ 0 3 0.4 0.5 0.6 tance / Refel c 4 00E+012 6.00E+012 8.00E+012 ( α h ν ) 2

800 1000 1200 1400 1600 1800

0.0 0.1 0.2 0.3 T ransm it t

0 6 0 8 1 0 1 2 1 4 0.00E+000

2.00E+012 4.00E 012

800 1000 1200 1400 1600 1800

Wavelength (nm)

0.6 0.8 1.0 1.2 1.4

hν

Band gap is very close to the reported value of 1 02 eV

Band gap is very close to the reported value of 1.02 eV

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Sputtered in argon atmosphere from commercial In₂S₃ powder.

Films sputtered at different Films sputtered at different substrate temperatures

I di

S l hid Fil

Indium Sulphide Films

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XRD f I S Fil

XRD of In

₂

S

₃

Films

Pressure : 7 3x10-3_mbar

Pressure : 7.3x10 mbar Mode : Constant Power (25 W) Frequency : 100 kHz

(2 2 12) (1 0 15) (0 0 12) (206) (1 0 9 )

250 0C

(103)

(116

)

200 0C

ty (

a

rb

.u

)

150 0C

100 0C

In te n s it

Preferred (109)

orientation

Tetragonal –

β

In

₂

S

₃

10 20 30 40 50 60

2θ (degrees)

No Heating

Tetragonal

β

In

₂

S

₃

formed with

No heating !!

2θ (degrees)

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1.0

Optical and AFM studies of In

₂

S

₃

Films

No heating 100 0_C

Band gap decreased with

0.6 0.8

m

ittanc

e

200 nm 200 nm

decrease in sulphur content

0.0 0.2 0.4

Tra

n

sm _{No heating}

100 0C 150 0C 200 0C 250 0C

300 400 500 600 700 800 900 1000 1100

Wavelength (nm)

Deposition % In %S [% ]S Band Gap

200 nm 200 n

Temperature eV

Non heated 41.26 58.74 1.42 2.768

1000_C _41.84 _58.16 _1.39 _2.735

1500_C _42.86 _57.14 _1.33 _2.708

[% ]In

250 0_C

150 C 42.86 57.14 1.33 2.708

2000_C _43.5 _56.5 _1.29 _2.667

2500_C _48.51 _51.49 _1.20 _2.526

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Reactive sputtered in oxygen and Reactive sputtered in oxygen and argon atmosphere from

commercial In₂O₃ powder.

Fil tt d t diff t

Films sputtered at different oxygen flow rates with no additional heating

Indium Oxide Films

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In

₂

O

₃

Films

Pressure : 4.0x10-3_Pa

X-ray diffraction spectra

Mode : Constant Power (60W) Frequency : 60 kHz

MFC : F_Ar+ F_Oxygen = 20sccm

1000 1200

uni

t)

(222)

Thickness ~ 500 nm

200 400 600 800 n te n sity (a rb . 0 200 0 % 2.5 % 5 % I n (440) (400) (211)

Cubic bixbyite In₂O₃ phase.

20 30 40 50 60

5 % 10 %

2θ (deg)

Preferred (400) (440) orientation at higher O₂ concentration

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Resistivity of In

₂

O

₃

Films

4 5

Resistivity

5.09 Ω cm

2 3

s

ti

vi

ty (

Ω

cm

)

Strongly n-type 0 - 2.5% O₂

Weakly n-type 5 – 10% O₂

0 1

Re

si

s

0.00519 Ω cm

Weakly n type 5 10% O₂

0.00536 Ω cm

0 2 4 6 8 10

% of O₂in gas flow

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Optical Properties of In

₂

O

₃

Films

80 100 ) 60 m it tance ( % ) 1.25E+015 1.50E+015 1.75E+015 3.72 eV 10.0% oxygen flow

) 20 40 Trans m O

2 flow

0 % 2.5 % 5.0 % 3.64 eV 3.70 eV 3.67 eV 2.50E+014 5.00E+014 7.50E+014 1.00E+015 ( α h ν )2 (m -2.eV 2 )

300 400 500 600 700 800 900

0

Wavelength (nm)

5.0 % 10 % 3.72 eV

2.5 3.0 3.5 4.0 0.00E+000

hν (eV)

20

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23.66 nm

0% O_2.Ra – 2.63nm 2.5% O 28.35 nm

2 Ra – 3.06nm

AFM of In

₂

O

₃

Films

0.00 nm 200nm

30.43 nm 37.85 nm

5.0% O₂ Ra – 3.60 nm 10.0% O₂Ra – 4.64 nm

0.00 nm 200nm

21

References

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Conclusion

¾ The possibilities of pulsed d c magnetron sputtering for the deposition of Mo

¾ The possibilities of pulsed d.c magnetron sputtering for the deposition of Mo, CuInSe₂In₂S₃and In₂O₃ films from powdered targets were studied.

¾ The analysis showed that these PDMS grown films can be used for solar cell applications

applications.

¾ The most surprising outcome is the nearly stoichometric nature of the CIS films

largely irrespective of the starting composition of the material

¾ i l h d fil d d i h i i h h

¾ Single phase CIS and In₂S₃ films were produced using PDMS technique without the aid of additional substrate heating.

¾ Films grown from this single step process can cut down the cost and also the

d l i i h h i l b i d i h h

dangerous selenisation processes that have previously been associated with the production of high efficiency CIS solar cells.

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Acknowledgements

¾Prof. D.M. Bagnall, School of Electronics and Computer Science , University of Southampton.

¾Prof. P.J. Kelly, Manchester Metropolitan University.

¾Dr. J. Hisek, Technische Universität Braunschweig, Hannover, Germany

¾Dr. H. Yates, Materials and Physics Research Centre , University of Salford

¾Dr J S Cowpe Materials and Physics Research Centre University of Salford

¾Dr. J.S. Cowpe , Materials and Physics Research Centre , University of Salford

¾Mr. G. Parr, Salford Analytical Services, University of Salford.

¾Mr. J. Smith, Physics Technician , University of Salford.

¾Mr. M. Clegg, Physics Technician , University of Salford.

Finally , thanks to everybody who has indirectly helped to bring this work to fruition.

THANK FOR YOUR ATTENTION

23

email : [email protected]

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Pulsed D.C. Magnetron Sputtering System

0 5 10 15 20 25 30 35 40 45 50 55 0

100

T (μs) Pulse off Substrate (Anode) K-type Thermocouple Substrate (Anode) K-type Thermocouple

0 5 10 15 20 25 30 35 40 45 50 55

-300 -200 -100 V o lt age ( V ) Argon

S/S*_Cover

Camera MFC 100 sccm p Argon

S/S*_Cover

Camera MFC 100 sccm p -500 -400 Pulse on

Ideal pulsed d.c signal for 100kHz

N S N Cu -Target HolderMagnets Water Channel PTFE Insulator

S/S*_Base

Window

N S N Cu -Target HolderMagnets Water Channel PTFE Insulator

S/S*_Base

Window Water cooling Turbo & Rotary pump Substrate Heater + Ni-Cr Ni-Al Water cooling Turbo & Rotary pump Substrate Heater + Ni-Cr Ni-Al

AE Pinnacle Plus Power Supply

Rotary pump

+

-AE Pinnacle Plus Power Supply

Rotary pump

+

-4

Reference

S. Karthikeyan et al, Vacuum, 2010, 85; pp.634-638.

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SEM and AFM CuInSe

₂

Films

~180-210 nm particle size

From stoichiometric powder From 5% extra Se powder From 5% extra In powder 180 210 nm particle size

500 nm 500 nm 500 nm

1 7