FABRICATION AND CHARACTERIZATION OF ZnxCd1-xS/CdTe THIN FILM SOLAR CELLS ON ITO AND FTO COATED

GLASS SUBSTRATES

M.S. Hossain, N.A. Khan, M. Akhtaruzzaman, A. R. M. Alamoud and N. Amin

Solar Energy Research Institute (SERI)Universiti Kebangsaan Malaysia (UKM)

Selangor, Malaysia

PVSEC-25 GPVC 2015, November 15-20, 2015, Busan, Korea. Presentation No: CIS-O-25

Outline

Introduction: Solar Cell Classifications Prospects of ZnxCd1-xS for CdTe Solar Cells Structure of ZnxCd1-xS/CdTe Solar Cells

Objective Methodology Advantages of RF Magnetron Sputtering Result and Discussions Conclusion

Introduction

PV Cells

Thin Film

Poly-Crystalline

Silicon

Compound

Crystalline

Amorphous

Others

Mono-Crystalline

Mono-Crystalline

Poly-Crystalline

GaAs

CdTe,CIGS, CZTS

(Organic-Materials, Dye etc.)

PV Cell

Electricity

Heat

Sunlight

Prospects of ZnxCd1-xS for CdTe Solar Cells:

CdTe is considered as one of the leading materials for cost-effective photovoltaic (PV).

The bandgap of CdTe is around (1.5 eV), close to the ideal value for photovoltaic conversion efficiency. It has high optical absorption coefficient and high chemical stability.

The formation of a stable, low resistance, non-rectifying contact to p-CdTe thin-film is one of the major and critical challenges for efficient and stable CdTe solar cells.

ZnxCd1-xS window layer is preferable instead of CdS for CdTe solar cells in considering bandgap and prevention of excessive pinholes for film less than 100 nm.

Introduction (Cont)

ZnxCd1-xS/CdTe Solar Cell Structure

Objective

Growth optimization of ZnxCd1-xS film for CdTe solar cell through structural and morphological study. Effect of thickness variation on structural, morphological properties of CdTe thin films.Impact of ITO and FTO on the performance of ZnxCd1-xS/CdTe solar through RF magnetron sputtering

Methodology Glasses were cleaned in an ultra-sonic bath.

Cleaned glasses were dried by dry N2.

Complete ZnxCd1-xS/CdTe solar cells were deposited layer by layer onto ultrasonically cleaned glass substrates by RF sputtering technique.

After deposition, ZnxCd1-xS and CdTe were characterized through EDX, XRD and SEM analysis.

Complete cells were tested through I-V tester

Methodology (contd.)

Process Parameters of CdTe, BSF and Ag metal used in sputtering system

Sample No.

RF POWER (W)

Operating Pressure (mTorr)

Argon Flow

(sccm)

Substrate Temp. (0C)

CdTe Thickness

(μm)1 35 16 16 260 4.52 35 16 16 260 3.53 35 16 16 260 2.84 35 16 16 260 1.55 35 16 16 260 1.16 35 16 16 260 0.58

Process parameters ZnTe Cu Te Ag metal

Deposition Temp. 250 0C 250 0C 250 0C 250 0C

Base pressure 2×10-5 T 2×10-5 T 2×10-5 T2×10-5 T

Working pressure 18 mT 18 mT 18 mT 18 mTArgon gas flow 18 sccm 17 sccm 17 sccm 16 sccmRF power 50 W 50 W 40 W 50 WApprox. thickness 100 nm 40 nm 60 nm 100 nm

Advantages of Magnetron Sputtering The sputtering technique is well suited for industrial large scale production and it has been applied successfully to CdTe solar cell fabrication .

The deposited film thickness can be monitored and controlled to achieve any thickness from nm to μm.

All the layers of the designed cellswith desired thickness can be deposited in one chamber by sputtering, without breaking the vacuum RF magnetron Sputtering machine used in this work

Results and Discussion EDX and XRD Analysis of ZnxCd1-xS Thin Film

Figure: EDX and XRD spectra of ZnxCd1-xS thin film

Results and Discussion (contd.)

Figure : Surface and cross-section images of ZnxCd1-xS thin films.

SEM Analysis of ZnxCd1-xS Thin Film

Results and Discussion (contd.)

The (111) orientation is the close packing direction of zinc-blende structure and this type of orientation is often observed in poly crystalline films.

XRD Analysis of CdTe Thin Film

Results and Discussion (contd.)

Figure : Surface and cross-section images of CdTe thin film for variable thickness (1.1 μm and 4.5 μm)

Results and Discussion (contd.) Cells fabricated in ITO coated glasses show a bit higher performance than cells fabricated in FTO coated glasses

Figure : J-V characteristics of ZnxCd1-xS/CdTe solar cell in which back contact deposited by sputtering and BSF used as ZnTe for optimization of ITO and FTO with CdTe 4.5 μm and 1.1 μm

Results and Discussion (contd.)

Figure : J-V characteristics of ZnxCd1-xS/CdTe solar cell in which back contact deposited by sputtering and BSF used as Cu2Te for optimization of ITO and FTO with CdTe 4.5 μm and 1.1 μm

Cells fabricated with ZnTe BSF show a bit higher performance than cells fabricated with Cu2Te in comparing the result in the previous slide.

Conclusion

The structural and morphological study of window and absorber layers of ZnxCd1-xS/CdTe solar cells have been investigated by XRD, EDX and SEM analysis.

The complete ZnxCd1-xS/CdTe solar cells fabricated in ITO and FTO coated glasses with different BSF (ZnTe, Cu2Te) have been examined.

Cells fabricated in ITO coated glasses using ZnTe BSF result better performance in comparison to FTO coated glass cells using Cu2Te BSF.

THANK YOU

Q & A