Identification of Defects and Secondary Phases in Reactively Sputtered Cu2 ZnSnS4 Thin Films

Июль 24, 2022

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Identification of Defects and Secondary Phases in Reactively Sputtered Cu2 ZnSnS4 Thin Films

Содержание

2. Outline Motivation Problems with characterization of thin films Experimental approach Results X-ray diffraction Raman Spectroscopy Transmission
3. Motivation – Phase Equilibrium CZTS is a line compound between Cu2SnS3 and ZnS Theoretically even a
4. Motivation – Crystal Structure Crystal structures of secondary phases similar to CZTS All primary peaks overlap
5. Experimental Approach Substrate Cu Zn Sn Introduce H2S into chamber during sputter deposition Sulfur is incorporated
6. Characterization - XRD Varying Zn/(Cu+Sn) Ratio Zn/(Cu+Sn) ratio is varied while holding Cu/Sn ratio constant Impossible
7. Characterization - XRD Varying Cu/(Zn+Sn) Ratio Cu/(Zn+Sn) ratio is varied while holding Zn/Sn ratio constant Need
8. Characterization – Raman Varying Zn/(Cu+Sn) Ratio Raman spectra show only minor changes even though composition is
9. Device Fabrication Glass Substrate 3000 µm Molybdenum Layer 1 µm 1.75 µm CdS (n-type) 55 nm
10. Device Characterization I-V Measurement EQE Measurement First CZTS devices grown by a reactive sputtering process Efficiency
11. Characterization - TEM 500nm Detrimental secondary phase interspersed in CZTS matrix Stacking faults in the secondary
12. Characterization - Auger Raster beam over sputtered surface of sample and scan for Cu, Zn, Sn
13. Characterization - CdZnS Cd penetration into ZnS lowers the cubic-hexagonal transition temperature Stacking faults in TEM
14. Characterization - Auger Sn Cd Overlay Sn and Cd signal Cd ion exchanges with Zn during
15. Summary CZTS thin films were grown using Reactive Sputtering Films were characterized using X-ray Diffraction and
16. Acknowledgements US Department of Energy, Office of Basic Energy Sciences as part of an Energy Frontier
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Слайд 2

Outline
Motivation
Problems with characterization of thin films
Experimental approach
Results
X-ray diffraction
Raman Spectroscopy
Transmission Electron Microscopy
Scanning

Auger Microscopy
Summary & Acknowledgements

Слайд 3

Motivation – Phase Equilibrium
CZTS is a line compound between Cu2SnS3 and

ZnS
Theoretically even a 2-3% compositional variation could lead to phase separation

Ternary Phase Diagram

Binary Phase Diagram

Olekseyuk, I.D. "Phase Equilibria in the Cu2S-ZnS-SnS2 System." Journal of Alloys and Compounds. 368. (2004): 135-143. Print.

CZTS

Слайд 4

Motivation – Crystal Structure
Crystal structures of secondary phases similar to CZTS
All

primary peaks overlap and hard to separate
Low intensity peaks cannot be seen easily in thin films

Theoretical XRD Patterns of CZTS, Cu2SnS3, and ZnS

Слайд 5

Experimental Approach
Substrate
Cu
Zn
Sn
Introduce H2S into chamber during sputter deposition
Sulfur is incorporated into

the film in one step (no anneal)
Expect to see higher densities and improved film quality

Reactive Sputtering

Слайд 6

Characterization - XRD
Varying Zn/(Cu+Sn) Ratio
Zn/(Cu+Sn) ratio is varied while holding Cu/Sn

ratio constant
Impossible to determine difference between CZTS, CTS, and ZnS from XRD pattern

(101)

(200)

(220)

(312)

(112)

Olekseyuk, I.D. "Phase Equilibria in the Cu2S-ZnS-SnS2 System." Journal of Alloys and Compounds. 368. (2004): 135-143. Print.

Слайд 7

Characterization - XRD
Varying Cu/(Zn+Sn) Ratio
Cu/(Zn+Sn) ratio is varied while holding Zn/Sn

ratio constant
Need to get very far off 2:1:1 stoichiometry before any CuxS phases can be seen
CuxS can be removed with KCN etch

(101)

(200)

(220)

(312)

(112)

Olekseyuk, I.D. "Phase Equilibria in the Cu2S-ZnS-SnS2 System." Journal of Alloys and Compounds. 368. (2004): 135-143. Print.

Слайд 8

Characterization – Raman
Varying Zn/(Cu+Sn) Ratio
Raman spectra show only minor changes even

though composition is varied dramatically
No evidence of the CuxS phase shown by other groups at growth temperatures higher than 500C

Varying Cu/(Zn+Sn) Ratio

Слайд 9

Device Fabrication
Glass Substrate
3000 µm
Molybdenum Layer
1 µm
1.75 µm
CdS (n-type)
55 nm
ZnO:Al (n-type)
340 nm
Aluminum

Grid

CZTS Absorber (p-type)

CZTS Device Stack

Zn-rich films incorporated into standard CIGS device stack for testing

ZnO

85 nm

ZnO

ZnO:Al

CdS

CZTS

SEM Image

Слайд 10

Device Characterization
I-V Measurement
EQE Measurement
First CZTS devices grown by a reactive sputtering

process
Efficiency = 1.35%
Degraded EQE clearly points to undetected defects in the absorber

Слайд 11

Characterization - TEM
500nm
Detrimental secondary phase interspersed in CZTS matrix
Stacking faults in

the secondary phase point to a transition between cubic and hexagonal crystal structures

Слайд 12

Characterization - Auger
Raster beam over sputtered surface of sample and scan

for Cu, Zn, Sn
Overlay Cu, Zn, Sn signal
Composition variation points to CZTS / ZnS (Zn-rich)

2 um

CZTS

ZnS

Слайд 13

Characterization - CdZnS
Cd penetration into ZnS lowers the cubic-hexagonal transition temperature
Stacking

faults in TEM images are created during CBD of CdS layer

CdS – ZnS Phase Diagram

(101)

H-ZnS

(220)

(312)

(112)

XRD before and after CBD

C + H

Chen et al.“Solid State Phase Equilibria in the ZnS-CdS System." Materials Research Bulletin. 23. (1988): 1667-1673. Print.

Слайд 14

Characterization - Auger
Sn
Cd
Overlay Sn and Cd signal
Cd ion exchanges with Zn

during bath deposition and penetrates the ZnS phase

CZTS

CdZnS

2 um

Слайд 15

Summary
CZTS thin films were grown using Reactive Sputtering
Films were characterized using

X-ray Diffraction and Raman Spectroscopy
Full devices have been grown and tested but are limited due to secondary phases in the films
Transmission Electron Microscopy and Scanning Auger Microscopy can be used to identify these secondary phases

Слайд 16

Acknowledgements
US Department of Energy, Office of Basic Energy Sciences as part

of an Energy Frontier Research Center
http://www.er.doe.gov/bes/EFRC/index.html
Applied Quantum Technologies
Local thin film solar startup
http://www.aqtsolar.com

Identification of Defects and Secondary Phases in Reactively Sputtered Cu2 ZnSnS4 Thin Films

Содержание

OutlineMotivationProblems with characterization of thin filmsExperimental approachResultsX-ray diffractionRaman SpectroscopyTransmission Electron MicroscopyScanning

Motivation – Phase EquilibriumCZTS is a line compound between Cu2SnS3 and

Motivation – Crystal StructureCrystal structures of secondary phases similar to CZTSAll

Experimental ApproachSubstrateCuZnSnIntroduce H2S into chamber during sputter depositionSulfur is incorporated into

Characterization - XRDVarying Zn/(Cu+Sn) RatioZn/(Cu+Sn) ratio is varied while holding Cu/Sn

Characterization - XRDVarying Cu/(Zn+Sn) RatioCu/(Zn+Sn) ratio is varied while holding Zn/Sn

Characterization – RamanVarying Zn/(Cu+Sn) RatioRaman spectra show only minor changes even

Device FabricationGlass Substrate3000 µmMolybdenum Layer1 µm1.75 µmCdS (n-type)55 nmZnO:Al (n-type)340 nmAluminum

Device CharacterizationI-V MeasurementEQE MeasurementFirst CZTS devices grown by a reactive sputtering

Characterization - TEM500nmDetrimental secondary phase interspersed in CZTS matrixStacking faults in

Characterization - AugerRaster beam over sputtered surface of sample and scan

Characterization - CdZnSCd penetration into ZnS lowers the cubic-hexagonal transition temperatureStacking

Characterization - AugerSnCdOverlay Sn and Cd signalCd ion exchanges with Zn

SummaryCZTS thin films were grown using Reactive SputteringFilms were characterized using

AcknowledgementsUS Department of Energy, Office of Basic Energy Sciences as part

Похожие презентации

Outline
Motivation
Problems with characterization of thin films
Experimental approach
Results
X-ray diffraction
Raman Spectroscopy
Transmission Electron Microscopy
Scanning

Motivation – Phase Equilibrium
CZTS is a line compound between Cu2SnS3 and

Motivation – Crystal Structure
Crystal structures of secondary phases similar to CZTS
All

Experimental Approach
Substrate
Cu
Zn
Sn
Introduce H2S into chamber during sputter deposition
Sulfur is incorporated into

Characterization - XRD
Varying Zn/(Cu+Sn) Ratio
Zn/(Cu+Sn) ratio is varied while holding Cu/Sn

Characterization - XRD
Varying Cu/(Zn+Sn) Ratio
Cu/(Zn+Sn) ratio is varied while holding Zn/Sn

Characterization – Raman
Varying Zn/(Cu+Sn) Ratio
Raman spectra show only minor changes even

Device Fabrication
Glass Substrate
3000 µm
Molybdenum Layer
1 µm
1.75 µm
CdS (n-type)
55 nm
ZnO:Al (n-type)
340 nm
Aluminum

Device Characterization
I-V Measurement
EQE Measurement
First CZTS devices grown by a reactive sputtering

Characterization - TEM
500nm
Detrimental secondary phase interspersed in CZTS matrix
Stacking faults in

Characterization - Auger
Raster beam over sputtered surface of sample and scan

Characterization - CdZnS
Cd penetration into ZnS lowers the cubic-hexagonal transition temperature
Stacking

Characterization - Auger
Sn
Cd
Overlay Sn and Cd signal
Cd ion exchanges with Zn

Summary
CZTS thin films were grown using Reactive Sputtering
Films were characterized using

Acknowledgements
US Department of Energy, Office of Basic Energy Sciences as part