Photovoltaic structuresby chemical deposition

P. K. Nair, Harumi Moreno, Sarah Messina, David Avellaneda, M. T. S. Nair

Centro de Investigación en EnergíaUniversidad Nacional Autónoma de México

Temixco, Morelos 62580, Méxicopkn@cie.unam.mx

Jose Campos, Oscar GomezDaza, Ma. Luisa Ramon G.

Pilkington-Toledo OH, BHEL-Gurgaon

Funding: CONACYT, Mexico; DGAPA-UNAM

Solace2008, Kochi

Outline

Just how many solar cell technologies..?

Chemical deposition and scope for new solar cell technologies

Chemically deposited photovoltaic structures

Prospects

Just how many solar cell technologies..?

1950 1960 1970 1980 1990 2000

5

10

15

20

25E

ffici

ency

(%)

Year

crystalline Siamorphous Sinano TiO2CIS/CIGSCdTe

>25 SHV

HW

LHW

MW

LW

FW

Nathan S. Lewis, www.caltech.edu

Just how many solar cell technologies..?

Worst day insolation map (kWh/m2/day ) PV sellers’ strategic web map

Just how many solar cell technologies..?

6 Boxes at 3.3 TW each; Nathan S. Lewis, www.caltech.edu

Just how many solar cell technologies..?

Just how many solar cell technologies..?Semicond. Mexican

Production (2004)

William W. Porterfield, Inorganic Chemistry: a united approach, Academic 1993 San Diego, p. 9.

Ag (3,000 ton)

www.inegi.gob.mx

Abundance: Cd, 0.1 ppm; Te, 0.005 ppm; In, 0.05 ppm; Ga,15 ppm; Ru, 0.0001ppm

At system efficy. of 10%, for 100,000 TWh/yr PV electricity

Solar cell Mater. req. Total req.

Total req/ resources

CdTe (1.5 µm) 4.7 g/m2 of Te 2,400,000 m.tons

110

CuIn0.75Ga0.25Se2 (2 µm) 2.9 g/m2 of In 1,400,000 m.tons

650

Potential to reduce materials exists: only 0.5 µm of CIGS and 1.0 µm of CdTeare needed to absorb 90% of the photons

B. A. Andersson, et al, Energy, 23 (1998) 407 – 411; Energy Policy 28 (2000) 1037-1049

Just how many solar cell technologies..?

A Statement of Understanding

• Photovoltaic technologies meeting the future demand for photovoltaic modules would complement each other.

• There is room for developing distinct technologies making use of local/regional raw materials and appropriate technologies to satisfy local need.

Chemical depositionscope for new solar cell

technologies

Chemical deposition – by flotation

Optimization of: 1. composition of bath mixture

2. quantity of bath per surface area of the substrate

3. duration and temperature of deposition

4. post deposition processing and/or multilayer deposition

Chemical deposition – solar radiation control and low-efficiency solar cells..

End use saving 40%, PV gen 5%

a great step forward!

Tvis 20%, Tsol 13%, Rsol 16%, Asol 71%

Heat transfer - G. Alvarez, et al: Solar Energy 78 (2005) 113; Mechanical - J. O. Aguilar, et al: Surf. Coat. Technol. 200(2005) 2557

Chemical deposition – by immersion

Chemical deposition – scope for solar cells..

980 W/m2

180 W/m2

Chemical deposition – scope for low efficiency solar cells..

www.sunwize.com grid-tieD. E. Carlson talk, 2006

Create comfort space with a solar roof; the value added is welcome!

Then 5% PV/solar control roof too has a role to play!

chemical deposition:scope for low efficiency solar cells

PV cells inside cellular plastic sheets – no lamination or

support structures

Sheet area: 15 sheets x 1.5 square meter: 22.5 sq mPV power @ 5% efficiency ≈ 1 kWe

And we also just created 22.5 sq m of valuable comfort zone underneath!

Hu, Nair, PET: J. Cryst.Growth 152(1995)150; Nair et al, Polyethersulfone: Thin Solid Films, 401(2001) 243; J. Cardoso et al, polyimide: Semicond Sci. Technol. 16 (2001) 123

solar cells from 100,000 production plants- a possibility?

Task force : (i) Transparent conductors, (ii) Buffers and windows, (iii) Absorbers (iv) Contacts, sealing and encapsulation

Chemically deposited photovoltaic structures

Chemically deposited semiconductor thin films…

CdS direct ~ 2.45 eVZnS direct ~ 3.7 eVZnSe direct ~ 2.7 eV

CdSe direct ~ 1.7 - 2.0 eVSb2S3 direct ~ 1.7 - 1.8 eVSnS direct ~ 1.6 eV

CuSe, Cu2-xSe direct ~ 2.1 – 2.3 eV; indirect, ~ 1.2 - 1.4 eV

CuS, Cu1.8S, Cu1.96S direct, ~ 1.55 - 1.4 eV

Bi2S3 direct ~ 1.4 – 1.5 eVSb2Se3 indirect? ~ 1 – 1.2 eVTl2S direct ~ 1.12 eV, Bi2Se3 direct ~ 1.08-1.06 eV Ag2S direct ~ 1 eVPbS direct ~ 0.4 – 0.7 eV PbSe direct ~ 0.6 eV(?)

CuSbS2, Cu3SbS4, AgSbSe2, Cu3BiS3, Cu4SnS4, Cu2SnS3,

TlSbS2, TlSbS2

P. K. Nair, et al, Sol. Energy Mater. Sol. Cells, 52, 313 (1998) Gary Hodes: Chemical Solution Deposition of Semiconductor Films,

Marcel Dekker 2003

Chemically deposited photovoltaic structures..

0.5 1.0 1 .5 2. 0 2.5 3.0 3.5 4.0102

103

104

105

106

CdS(cub)2.45 eV

Sb2(S/Se)

3

1 eV

Sb2 S3 1.7 eV

Optical Absorption Coeff ic ients of Chemically Deposited Thin Filims

PbS0.6 eV

ZnS3.45 eV

ZnO3.4 eV

CdS( hex)2.6 eV

SnS(cub)1.75 eV

Bi2S3 1.6 eV

α (c

m)-1

hυ (eV)

95% abs, 300 nm

For quantum size effects...G. Hodes, Phys. Chem. Chem. Phys. 9(2007) 2181-2196

Optical Conversion Efficiency: (i) photon absorption and e-h generation;(ii) Separation of e-h across the depletion region (iii) collection and work

Optical

Effic. %

Optical band gap Eg(eV)

Carrier multiplication at hν > 2Eg and super efficiencies ..? G. Nair, M. Bawendi, Phys. Rev. B 76, 081304(R) (2007)

Chemically deposited photovoltaic structures…

SnO2:F-CdS-SnS(A)-CuS-AgCdS (100 nm) - 0.1 M cadmium nitrate,1 M sodium citrate,

ammonia (aq), 1M thiourea,; 80 oC, 3h; predominantly hexagonal; photoconductive with conductivity σ~ 10-3 – 10-2 (Ω cm)-1, can be doped n-type; Eg ~ 2.6 eV

SnS - (Bath A) (100 nm)

CuS – 0.5 M CuCl2, 3.7 M triethanolamine, 30% NH3 (aq),1 M NaOH1 M thiourea; 30 oC, 30 min - 1 h; covellite (hexagonal); p-type conductivity, σ ~ 103 (Ω cm)-1; Eg indir. ~ 1.55 eV

315 oC in 300 mTorr Nitrogen

Avellaneda, Nair, Nair, Thin-Film Compound Semiconductor Photovoltaics—2007, MRS. Symp. Proc. Volume 1012 (2007), 1012-Y12-29 (on line)

20 30 40 50 600

255075

100

2 θ (deg)

SnS- herzenbergite PDF# 39-0354

a)

(%)

X-ra

y in

tens

ity(r

elat

ive)

b)

c)

0255075

100

(222

)

(311

)

(220

)

(200

)Zinc Blende (a = 5.7911)

(111

)

Structural data on SnS thin films

XRD patterns of a) acetone bath, b)acetic acid bath, ZB as prepared, c)SnS ZB annealed in N2, 1h 300 mTorr, 350ºC

Ref:E. C. Greyson, et al, “ Tetrahedral Zinc Blende Tin Sulfide Nanoand Microcrystals", Small 2 (2006) 368-371.

Anneal: Changes in Composition

a)SnS+Se annealed at 300 ºC, N2 along with the standard pattern of SnSe (PDF 38105); c)SnS+200 mg of S, annealed at 300 ºC, N2; d)SnS annealed in air at 400 ºC; e)SnS annealed in air at 550 ºC,

1,5 2,0 2,50

1

2

3

4

5

hν (eV)

(αhν

)2/3 (

103 c

m-2

/3eV

2/3 )

1.7 eV1.6 eV

After heating

Before heating

Optical properties of SnS ZB thin films annealed in air at differenttemperatures, and in the presence of Se, and S.

500 1000 1500 2000 25000

20

40

60

80

100

0

20

40

60

80

100

R %

W avelength (nm)

T %

550º 500º 400º 300ºC As prepared

Optical properties

SnO2:F/CdS-SnS(A)/CuS/Ag

-0,2 0,0 0,2 0,4

-1,5

-1,0

-0,5

0,0

0,5C

urre

nt (

10-4

A) Voltage (V)

Cu2SnS3

SnS

luz

CdS

Pintura de plata

SnO2:F

0.36FF6 kΩRp

300 ΩRs

200 mVVm

340 mVVoc

3.0A

3.7 mA/cm2Jm

6.0 mA/cm2Jsc

6.4 mA/cm2Jp

5x10-2 mA/cm2Jo

0.36FF6 kΩRp

300 ΩRs

200 mVVm

340 mVVoc

3.0A

3.7 mA/cm2Jm

6.0 mA/cm2Jsc

6.4 mA/cm2Jp

5x10-2 mA/cm2Jo

J = Jo [ exp(q(Voc-JRS)/AkBT) – 1] + [(V-JRS)/RP ] - JP

FF= Jm Vm/ Jsc Voc, Lambert W function used.

MRS Proc. Volume 1012, 2007, 1012-Y12-29

SnOSnO22:F /CdS/SnS(1,2)/:F /CdS/SnS(1,2)/CuSCuS--AgAg

-0.2 0.0 0.2 0.4 0.6 0.8

-7.7

-3.8

0.0

3.8

7.7

11.5

15.4

19.2

23.1 DARK LIGHT

J sc (m

A/cm

2 )

Voltage (V)

VOC = 380 mVJSC = 7.7 mA/cm2

Vm = 220 mVJm = 4.53 mA/cm2

FF = 0.34Eff. = 1%

SnS (1)SnS (2)

IL= 850 W/m2

SnO2:F

CuS

CdS

SnO2:F/CdS/SnS/PbS/Ag

-0,2 0,0 0,2 0,4

-8

-6

-4

-2

0

2

Voltage (V)

Cur

rent

(10-6

A)

0.27FF

70 kΩRp

90 ΩRs

160 mVVm

300 mVVoc

2.7A

0.247 mA/cm2Jm

0.484 mA/cm2Jsc

0.485 mA/cm2Jp

1x10-3 mA/cm2Jo

0.27FF

70 kΩRp

90 ΩRs

160 mVVm

300 mVVoc

2.7A

0.247 mA/cm2Jm

0.484 mA/cm2Jsc

0.485 mA/cm2Jp

1x10-3 mA/cm2Jo

-0,2 0,0 0,2 0,4

-2

-1

0

1

Cur

rent

(10-5

A)

Voltage (V)

0.28FF

22 k ΩRp

650 Ω (Area 1 mm2)

Rs

180 mVVm

320 mVVoc

2.2A

0.83 mA/cm2Jm

1.6 mA/cm2Jsc

1.7 mA/cm2Jp

1x10-3 mA/cm2Jo

0.28FF

22 k ΩRp

650 Ω (Area 1 mm2)

Rs

180 mVVm

320 mVVoc

2.2A

0.83 mA/cm2Jm

1.6 mA/cm2Jsc

1.7 mA/cm2Jp

1x10-3 mA/cm2JoSnS(A)

SnS(B)

PbS:1 M lead nitrate, 1 M NaOH, 1 M thiourea, 1 M triethanolamine; 40 oC, 2 h

Sb2S3 and Sb2SxSe3-x

Sb2S3 (i) Thin FilmsSbCl3, acetone, Na2S2O3

Sb2S3 (ii) Thin FilmsPotasium antim. tart,TEA, ammoniaThioacetamide

Selenium Thin FilmsNa2SeSO3 → Se (@ pH 4.5) 0 1 2 3 4 5 6 7 8 9 10

0

100

200

300

400

500

600

700

Growth curve of Sb2S3 at diferent temperature

Thic

knes

s (n

m)

Deposition duration (h)

-3 °C 1 °C 5°C 10 °C

(i) M T S Nair, et al J. Electrochem. Soc. 145 (1998) 2113(ii) O Savadogo, K C Mandal, Solar Energy Mater. 26 (1991) 117; (Se) K. Bindu, et al, Semicond. Sci. Technol., 17 (2002) 270.

Sb2S3-xSex formationx=0.75, calculated from XRD data

Eg direct 1.3 eV; orthorhombic: a =11.81 Å, b=11.47 Å, c=3.71 Åα , 105 cm-1 in the visible; conductivity, ≈ 10-8 Ω-1cm-1

XRD: Sb2S3 film heated in contact with Se film, 300oC

1 0 2 0 3 0 4 0 5 0

1 0 2 0 3 0 4 0 5 0

S b2S

xS e

3 -x

(211

)

(420

)

(301

)

(221

)

θ = 0 .5 °

(230

)

b )

θ = 1 .5 °

(420

)

Inte

nsity

[a.u

.]

2 θ [d e g re e s ]

S b 2S 3

P D F # 4 2 -1 3 9 3

(120

)

a )

(520

)

(301

)

(140

)

(211

)

(320

)

(200

)

(310

)

(220

)

(110

)

(130

)(3

10)

(120

)

(020

)

S b 2S e 3 P D F # 1 5 -0 6 8 1

(520

)

(321

)

Sb2S3 and Sb2(S/Se)3absorber thin films

1.5 2.0 2.5 3.00.0

5.0x103

hν [eV]

(αhν

)2/3 [e

V cm

-1]2/

3

Eg=1.76 eV

1.0 1.5 2.0 2.50

1000

2000

3000

4000

5000

1.0 1.5 2.0 2.50

1000

2000

3000

4000

5000

Eg=1,38

Se+Sb2S3 horneado a 300°C en N2

(αhν

)2/3 [e

Vcm

-1]2/

3

hν [eV]

Eg=1,31

Sb2S3 + Se horneado a 300°C en N2

(αhν

)2/3 [e

Vcm

-1]2/

3

hν [eV]

500 1000 1500 2000 25000

20

40

60

80

100500 1000 1500 2000 2500

0

50

Tran

smitt

ance

(%)

Wavelength (nm)

Sb2S3

Sb2(S/Se)3

Ref

lect

ance

(%)

Chemically deposited photovoltaic structures…

Sarah Messina, Nair, Nair Communicated 2007

Chemically deposited photovoltaic structures…

Sarah Messina, Nair, Nair Communicated 2007

Chemically deposited photovoltaic structures…

Sarah Messina, Nair, Nair Communicated 2007

500 1000 1500 2000 25000

20

40

60

80

100

TCO-CdS-(Sb2S

3+Se)-PbS

TCO-CdS-Sb2S

3+ Se

TCO-CdS-Sb2S

3

TCO-CdS

Tran

smitt

ance

[%]

Wavelength [nm]

SnOSnO22:F/:F/CdS(CubCdS(Cub, , hexhex)/Sb)/Sb22(S/Se)(S/Se)33/PbS/PbS--AgAg

0.0 0.2 0.4 0.6

-10

0

10 Ag PbS (200 nm)Sb

2(S/Se)

3 (250 nm)

CdS (cub) (90 nm)

SnO2:F

Voc=480 mVJsc=6 mA/cm2

FF= 0.38η= 1.4 %

Cur

rent

Den

sity

(mA/

cm2 )

Voltage (V)

0.0 0.2 0.4 0.6 0.8 1.0

-10

-5

0

5

10

15

AgPbS (200 nm)Sb2(S/Se)3 (500 nm)

CdS(hex) (200 nm)

Voc=640 mVJsc=7.5 mA/cm2

FF=0.26η=1.56%

Cur

rent

Den

sity

(mA

/cm

2 )Voltage (V)

Sb2(S/Se)3:D.Y. Suárez-Sandoval et al., J. Electrochem. Soc. 153 (2006) C91-C96.

SnO2:F/CdS/Sb2S3 /SnS/CuS-Ag

-0.2 0.0 0.2 0.4 0.6

-6.0x10-5

-4.0x10-5

-2.0x10-5

0.0

2.0x10-5

Curva I-V de la estructura FV SnO2-CdS-Sb2S3-SnS-CuS

Voc= 450 mVIsc = 40 µA; Jsc= 4 mA/cm2

A = 1 mm2

IL = 1 kW/m2

corr

ient

e [A

]

voltaje [V]

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-5.0x10-7

0.0

5.0x10-7

1.0x10-6

1.5x10-6

2.0x10-6

2.5x10-6

Curva IV de la estructura FV SnO2-CdS-Sb2S3-SnS-CuS

corr

ient

e [A

]

voltaje [V]

CdS

SnO2

SnS

IL=1000W/m2

silver print

Sb2S3

CuS

Voltage (V)

Voltage (V)

Current (A) Current (A)

Photoconductivity in CdS and PbS thin films

0 60 120 1801E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5σ = 0.1 (Ωcm)-1

σ = 10-7 (Ωcm)-1

CdS (Cubic)

100 nm60 nm

bias 10 V

Cur

rent

(A)

Time (s)

-0.2 0.0 0.2 0.4 0.6

-1.0x10-5

0.0

1.0x10-5

2.0x10-5

3.0x10-5

4.0x10-5

5.0x10-5

6.0x10-5

-0.2 0.0 0.2 0.4

-2.0x10-5

-1.0x10-5

0.0

1.0x10-5

Curva IV de la estructura fotovoltaica CdS-PbS IL=1 kW/m2

Voc = 297 mVIsc = 13 µA; 0.3 mA/cm2 A = 4 mm2

IL = 1 kW/m2 tung-hal

Cor

rient

e (A

)

Voltaje (V)

+-

Lost generation cells...? CdS(100 nm)/ PbS(250nm)S. Watanabe, Y. Mita, J. Electrochem. Soc. 166 (1969) 989

dark Voltage (V)

Voltage (V)

Cur

rent

(A)

Cur

rent

(A)

dark

photo

n-CdS Eg : 2.5 eV dir - windowp-PbS Eg : 0.4 eV ind –absorb.

CdS: M.T.S. Nair, P.K. Nair, J.Campos Thin Solid Films 161 (1988) 21-34

PbS: P.K. Nair, M.T.S. Nair J. Phys. D: Appl. Phys 23 (1990) 150-155

Glass/plastic

SnO2:F/CdS(hex 100 nm)/PbS(250 nm)/Ag

-200 0 200 400 600 800 1000

-10

-5

0

5

10

15

20

J (m

A/cm

2 )

Voltage (mV)

Dark

-200 0 200 400 600

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0 Light

VOC = 0.5 VJSC = 2.3 mA/cm2

A = 1mm2

L = 850 W/m2J

(mA

/cm

2 )

Voltage (mV)

+-

SnO2:F

CdSPbS

850 W/m2

TCO-coated glass from Pilkington, Toledo,USA; BHEL, Gurgaon-India

-300 -200 -100 0 100 200 300 400 500 600

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

TCO-CdS(hexagonal)-Bi2S3-PbS

J SC

(mA

/cm

2 )

Voltaje (mV)

Oscuridad Iluminacion

VCA = 340 mVJCS = 10 mA/cm2

A= 1.3 mm2

SnOSnO22:F/:F/CdS(CubCdS(Cub, , hexhex)/)/BiBi22SS33 /PbS/PbS--AgAg

PbS

SnO2:F CdSBiBi22SS33

Chemically deposited photovoltaic structures..

-100 0 100 20 0 300 400 500

-8000

-6000

-4000

-2000

0

2000

-

24 mm 2

Ag + 200 nm

60 nm

PbS

SnO2:F

Bi 2S3

80 nmZnO-

B

A

A (1000 W/m2)V

OC = 2 20 mV

JSC

= 6.2 mA/cm2

B (3000 W/m2)V

OC = 300 mV

JSC

= 21 mA/cm2

I (µA

)

V (mV)

Prospects

Photo-accelerated chemical deposition

Nair, Nair on CdS: Solar Energy Mater 15 (1987) 431

Nair et al on PbS: J. Phys. D. Appl. Phys. 24 (1991) 1466; Adv. Mater. Optics Electr. 1 (1992) 117; Semicond. Sci. Technol. 7 (1992) 239

Nair et al on Bi2S3: J. Electrochem. Soc. 140 (1993) 1085

PbS: bluish purple on goldenArt work by

Adrian Oskamsunlight

Bi2S3: purple on golden golden on purple

Some Conclusions

Photovoltaic technologies meeting the future demand for photovoltaic modules would complement each other

There is room for developing distinct technologies making use of local/regional raw materials to satisfy local needs

Easy scale-up and low-capital intensive production are basic features of all-chemically deposited photovoltaic structures – promising for photovoltaic technology

Solace 2008, Kochi