ALD of Tin Monosulfide, SnS

ALD of Tin Monosulfide, SnS

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Citation

Sinsermsuksakul, Prasert, Adam S. Hock, Roy G. Gordon. 2011. ALD

of Tin Monosulfide, SnS. Proceedings of the AVS 58th Itnernational

Symposium and Exhibition, October 30 - November 4, 2011,

Nashville, TN: 1-18.

Citable link

http://nrs.harvard.edu/urn-3:HUL.InstRepos:33950783

We prese presented about 100 stoichiom orthorhom under cer diffraction loosely pa semicond films also for solar c spectrum sufficient absorber

ent a new proc d at the confe

0 to 250 oC. N

etric to within mbic structure rtain condition n. The morpho

acked plates, ucting with lig show strong cells with max

and over 104

to absorb mo material in th

equiax

PrasertSinse

Ha

*Em

cess for ALD rence. The pr No impurities w

n the measurin e normally fou ns a minor am ology of the fi

depending o ghtly p-type d photoconduc ximum efficien

4

cm-1 in the n

ost of the sola in-film solar c

xed columnar 1.E+00 1.E+02 1.E+04 1.E+06 ( cm 1) ermsuksakul, rvardUnivers mail:Gordon

of tin(II) sulfid rocess operat were detected ng accuracy o nd in the bulk mount of a cub lms varies fro n the substra

oping (1015 to

ctivity. Their o ncy. The optic near infrared). ar spectrum. T

cells made of

grains

0 2 4 6

1.00 1.25 1.50

Absorption c

AdamS.Hock

sity,Cambrid

@chemistry.h

de, SnS, from tes at low sub d in the depos of RBS, abou k material (as bic phase is a om dense equ te and growth

o 1016 holes c

optical band g cal absorption . Thus a very These propert earth-abunda

0 1.75 2.00 2.2

hv (eV) coefficient for 3

kandRoyG.

ge,MAUSA

harvard.edu

m H2S and a n

bstrate tempe sited materia

t + 1%. The p s in the minera also detected

uiaxed column h conditions. T

cm-3 and hole

gap is about 1 n is very stron small thickne ties make SnS ant and non-t

p

25 2.50 2.75 3.

film thicknesse

----110nm

----230nm ----380nm

Gordon*

novel tin sourc eratures, in th

l by XPS or R phase corresp al Herzenberg by X-ray and nar polycrysta The SnS film mobility > 6 c

.3 eV, which

ng (over 105c

ess, less than S a good can oxic materials

platelets

00

es

ce that will be e range from RBS. The films

ponds to the gite) , althoug

electron alline films to

s are

cm2 V-1 s-1). T

is nearly opti

cm-1 in the vis

n 0.5 micron, i ndidate for the

ALD

of

T

in

Monosulfide

SnS

ALD

of

Ti

n

Monosulfide

,

SnS

Prasert Sinsermsuksakul,

Adam S. Hock and Roy G. Gordon

Harvard University

Cambridge

MA

USA

Cambridge

,

MA

USA

Outline

Thin-film solar

cells

the need for solar

p

ower

p

earth-abundant, non-toxic absorber: SnS

ALD

process

for

SnS

ALD

process

for

SnS

new tin precursor

growth per cycle

SnS

film properties

com

p

osition

p

structure

optical properties

electrical

properties

Harvard University

electrical

Global

Energy Use by Humans

Human energy use is currently ~ 14 terawatts (14 x 10

12

watts)

Sour

ce:

Inter

national

Ener

gy

Agenc

y

(I

EA)

Harvard University

Current energy supply is unsustainable-environmentally

, economically & socially

Source:

International

Energy

Agency

(IEA)

Solar

Radiation on Earth

Solar power is by far our most available energy source.

a

verage

solar

radiation

at

Earth

’ss

u

rf

a

c

e

~02k

W

/m

2

a

verage

solar

radiation

at

Earth

s

surface

~

0

.2

kW/m

2

The Earth’

s land area

receives

(1

10

14

2

)

(02k

W

/

2

)3

1

0

4

TW

(1

.5x

10

14

m

2

) x

(0

.2

kW/

m

2

) ~

3

x

10

4

TW

15%

ffi

i

t

l

d

l

0

3%

15%

e

ffi

c

ien

t so

lar mo

d

u

les on

0

.3%

of the Earth’

s total land area => 14 TW

Flat-Panel Photovoltaic Modules

Absorber

Material

Commercial

_P

V

Efficienc

y

Advantages

Limitations

y

cry

stalline Si

15-20%

high efficiency

high manufacturing

cost

amorphous

silicon

a

-Si

53

-63

%

low

cost

flexible

substrates

slow

deposition

low

efficiency

amorphous

silicon

,

a

-Si

5

.3

-6

.3%

low

cost

,

flexible

substrates

slow

deposition

,

low

efficiency

copper indium

gallium

diselenid

e

(CIGS)

8.1-1

1.0%

low cost,

moderate

efficiency

rare elements

(Ga, In)

cadmium telluride,

CdT

e

10.4%

low cost,

moderate

efficiency

toxic Cd,

rare

element

T

e

Dy

e-sensitized cells

-potential

for lowest

cost

long term

instability

Harvard University

CdT

e

PV modules

(First Solar

Inc.)

CIGS PV

module

(Global Solar

Inc.)

c-Si PV

module

(SunPower

Inc.)

a-Si PV

module

(Uni-Solar Inc.)

SnS: Alternate Absorber Layer in Solar PV

Cf

™

Basic

C

riteria

for the

Absorber

Material.

¾

Suitable bandgap

( Eg ~ 1.0-1.5

eV)

¾

High

quantum

yield

for

the

excited

carriers

¾

High

quantum

yield

for

the

excited

carriers

¾

Long diffusion

length /

low

combination velocity

Æ

PV

efficiency

Æ

PV

efficiency

¾

High optical absorption

coefficient (10

4

-1

0

5

cm

-1

)

Æ

small mass

of

material re

q

uired

q

¾

Constituent

elements are non-toxic

and

abundant

Æ

non-hazardous,

scalable, low cost

PV

SnS

has these properties

T

in(II) Amidinate

as ALD

Precursor

N

i

Pr

N

i

Pr

Sn

N

N

i

Pr

i

Pr

bis(

N,N’-diisopropylacetamidinato)tin(II)

Sn-N bonds => reactive

to

H

2

S

Chelate

structure

=>

thermal

stability

Chelate

structure

=>

thermal

stability

Hydrocarbon ligands

=>

volatility

Harvard University

6

R

X

UF

H

WH

P

S

H

UD

WX

UH

R

&

ALD Process for SnS

6

X

E

VW

UD

WH

WH

P

S

H

UD

WX

UH

R

&

6

R

X

UF

H

W

H

P

S

H

UD

WX

UH

R

&

6

X

E

VW

UD

WH

W

H

P

S

H

UD

WX

UH

R

&

*

UR

Z

WK

S

H

U

F\

FO

H

Q

P

1

R

LQ

G

X

FW

LR

Q

S

H

UL

R

G

6.00E+17 7.00E+17

ty

Sn

areal density vs

# of cycles

3.00E+17 4.00E+17 5.00E+17

real densi

oms/cm

2

)

2.00E+17 1.00E+17 0.00E+00

Temperature Dependence of

Growth

2

50E+16

3.00E+16

Sn

Areal Density vs. Substrate T

1.50E+16

2.00E+16

2

.50E+16

oms/cm

2

)

1.00E+16

(ato

5.00E+15

Sn

0.00E+00

100

150

200

250

300

Substrate temperature (

o

C)

Harvard University

SnS

Composition

5

X

WK

H

UI

R

UG

%

D

FN

VF

D

WW

H

UL

Q

J

6

S

H

FW

UR

VF

R

S

\

5

%

6

70

1.

2

1.4

1.

6

1.

8

En

er

g

y

(M

eV

)

50

60

Yield

SnS

20

30

40

No

rmalized

Y

SnS

1+

0.01

80

0

90

0

100

0

110

0

120

0

130

0

140

0

C

h

l

0

10

S

Cl

Sn

C

h

anne

l

SEM of SnS

Films Deposited at 120

o

C

200 cycles

1000 cycles

3000 cycles

5000 cycles

5000 c

y

cles

Harvard University

y

Distorted NaCl

Structure of SnS

Films

TEM

(+electron dif

fraction

)

literature

XRD

TEM

Miller

id

i

()

literature

XRD

TEM

in

di

ces

d

SnS

(Å)

d

XR D

(Å)

d

TEM

(Å)

hkl

22.01

4.035

4.001

3.87

11

0

26.01

3.423

3.404

3.33

120

27

47

3

244

3

243

021

27

.47

3

.244

3

.243

021

30.47

2.931

2.919

101

31.53

2.835

2.823

2.84

111

2.597

-2.53

121

39.05

2.305

2.302

2.29

131

44.73

2.024

2.021

2.02

141

45.49

1.9921

1.999

002

51.31

1.7791

-1.78

151

53.15

1.7219

1.722

122

56

67

1

6228

1

626

16

2

042

X-Ray Dif

fraction

(XRD)

56

.67

1

.6228

1

.626

1

.62

042

Orthorhombic Structure: a b

SnS

has Very Strong Optical Absorption

1.E+05 1.E+06

(cm

1

)

(1)

80

nm

films of various

thicknesses

D

> 10

4

cm

-1

for > 1.4 eV

1E

0

1

1.E+02

1.E+03

1.E+04

coef.

ption

(1)

80

nm

(2) 150

nm

(3) 210

nm

(4)

380

nm

(1)

(2)

(3)

(4)

D

> 10

5

cm

-1

for > 2.0 eV

1.E+00 1 .E + 01 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00

Absor

p

Photon energy h

Q

(eV)

(4)

380

nm

Ÿ

Solar cell

< 1

P

m thick

Ÿ

little material

needed

Band gap for thicker films ~ 1.3 eV

, optimum for solar cells

B

d

d

ith

i

i

fil

thi

k

B

an

d

gap

d

ecreases w

ith

i

ncreas

ing

fil

m

thi

c

k

ness

=> lar

g

e exciton diameter

, small effective mass, hi

SnS

is

an

absorber

for

earth

abundant

non

toxic

solar

cells

Summary

SnS

is

an

absorber

for

earth

-abundant

,

non

-toxic

solar

cells

ALD from tin(II) amidinate

and H

2

S => SnS

pure, stoichiometric, polycrystalline SnS

optical and electrical

properties suitable for thin solar cells

ALD suitable for prototype deposition of solar cells

(well-controlled composition and structure)

another possible application: thin-film transistors

on plastic

Harvard University

Acknowledgements

Hall measurements

done with Mark W

inkler and Eric Mazur

Support

from

the

Dreyfus

Foundation

Support

from

the

Dreyfus

Foundation