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

 Introduction:  Solar Cell Classifications  Prospects of Zn x Cd 1-x S for CdTe Solar Cells  Structure of Zn x Cd 1-x S/CdTe Solar Cells  Objective  Methodology  Advantages of RF Magnetron Sputtering  Result and Discussions  Conclusion

PV Cells Thin Film Poly-Crystalline Silicon Compound Crystalline Amorphous Others Mono-Crystalline Poly-Crystalline GaAs CdTe,CIGS, CZTS (Organic-Materials, Dye etc.) PV Cell Electricity Heat Sunlight

Prospects of Zn x Cd 1-x S 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.  Zn x Cd 1-x S 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.

 Growth optimization of Zn x Cd 1-x S 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 Zn x Cd 1-x S/CdTe solar through RF magnetron sputtering

 Glasses were cleaned in an ultra-sonic bath.  Cleaned glasses were dried by dry N 2.  Complete Zn x Cd 1-x S/CdTe solar cells were deposited layer by layer onto ultrasonically cleaned glass substrates by RF sputtering technique.  After deposition, Zn x Cd 1-x S and CdTe were characterized through EDX, XRD and SEM analysis.  Complete cells were tested through I-V tester

Process Parameters of CdTe, BSF and Ag metal used in sputtering system Sample No. RF P OWER (W) Operating Pressure (mTorr) Argon Flow (sccm) Substrate Temp. ( 0 C) CdTe Thickness ( μ m) Process parameters ZnTeCuTe Ag metal Deposition Temp C Base pressure 2×10 -5 T Working pressure18 mT Argon gas flow18 sccm17 sccm 16 sccm RF power50 W 40 W50 W Approx. thickness100 nm40 nm60 nm100 nm

 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 cells with desired thickness can be deposited in one chamber by sputtering, without breaking the vacuum RF magnetron Sputtering machine used in this work

 EDX and XRD Analysis of ZnxCd1-xS Thin Film Figure: EDX and XRD spectra of Zn x Cd 1-x S thin film

Figure : Surface and cross-section images of Zn x Cd 1-x S thin films.  SEM Analysis of ZnxCd1-xS Thin Film

 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

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

 Cells fabricated in ITO coated glasses show a bit higher performance than cells fabricated in FTO coated glasses Figure : J-V characteristics of Zn x Cd 1-x S/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 μ m and 1.1 μ m

Figure : J-V characteristics of Zn x Cd 1-x S/CdTe solar cell in which back contact deposited by sputtering and BSF used as Cu 2 Te for optimization of ITO and FTO with CdTe 4.5 μ m and 1.1 μ m  Cells fabricated with ZnTe BSF show a bit higher performance than cells fabricated with Cu 2 Te in comparing the result in the previous slide.

 The structural and morphological study of window and absorber layers of Zn x Cd 1-x S/CdTe solar cells have been investigated by XRD, EDX and SEM analysis.  The complete Zn x Cd 1-x S/CdTe solar cells fabricated in ITO and FTO coated glasses with different BSF (ZnTe, Cu 2 Te) have been examined.  Cells fabricated in ITO coated glasses using ZnTe BSF result better performance in comparison to FTO coated glass cells using Cu 2 Te BSF.

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