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09-10 December 2023, Green University, Bangladesh

Enhancing the Opto-electronic Performance of Cadmium Telluride

Thin-film Solar Cells Using Nanocone-shaped Surface Texturing

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Asif Al Suny, Samina Tohfa, Rifat Bin Sultan, Md. Hasibul Hossain, Tazrian Noor, Dr. Mustafa Habib Chowdhury

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IUB Photonics Simulation Laboratory

Department of Electrical & Electronic Engineering

INDEPENDENT UNIVERSITY, BANGLADESH

Paper ID: 602

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AGENDA

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PROBLEM STATEMENT

• Efficiency of CdTe thin-film solar cells (TFSCs) is relatively low, approximately 16-18%. [1]
• Surface-reflective loss is responsible for a considerable portion of the optical loss.[2]
• It causes around a 9% decrease in short circuit current density (Jsc) for CdTe solar cells [3]
• Surface texturing can a viable solution both in terms of surface reflection reduction and light trapping [4]
• The efficiency of thin-film/ultrathin CdTe solar cell can be significantly improved by surface texturing to integrate in portable electric devices and other applications

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WHY CdTe TFSC?

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• CdTe is more preferable due to its high absorption coefficient factor, low carbon footprint and production cost.
• Unlike Si, which is an indirect band gap material, CdTe is a direct band gap material.
• Therefore, the required absorbing layer thickness for efficient light absorption is significantly low (300-350 times tinner) compared to other commercially available TFSCs . [5]
• Cadmium (Cd) is found abundantly as a by-product of the zinc mining industry and thus Cd is relatively less prone to price fluctuations unlike Si.
• Currently, CdTe based solar cells have the major market share of the TFSC market compared to Si based solar cells. [Fraunhofer ISE]

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POSSIBLE USE OF CdTe BASED TFSCs

Watch

Transparent Window

Thermal Jacket

Smart Phone

Solar powered Car

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RESEARCH METHODOLOGY

• Commercially available Finite-Difference Time-Domain (FDTD) simulation tools designed by Lumerical Inc.

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• FDTD Solution solver was used, which utilizes the FDTD method, to perform the calculations for the optical enhancement analysis.

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• Device (CHARGE) solver was used for the electrical analysis.

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RESEARCH METHODOLOGY

Optical Nearfield

Conclusion: Optimal Nanocone Texture Morphology

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Fig. FDTD Simulation setup for optical analysis, using top and bottom monitors.

OPTICAL SIMULATION SETUP

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ELECTRICAL SIMULATION SETUP

Fig. CHARGE Simulation setup for electrical analysis

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RESULT AND DISCUSSION

Nanocone Diameter and Height Variation

A. Short Circuit Current Density (J_SC)

B. Open Circuit Voltage (V_OC)

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RESULT AND DISCUSSION

Nanocone Diameter and Height Variation

C. Fill Factor (FF)

D. Efficiency (ղ)

12.70% efficiency enhancement over

bare (η = 21.51%).

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RESULT AND DISCUSSION

E. Optical Absorption factor (g)

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RESULT AND DISCUSSION

Nanocone Pitch Variation

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RESULT AND DISCUSSION

Absorption Spectra Analysis

Average absorption of the absorber layer have increased from 64% to 82% for nanocone textured CdTe TFSCs

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RESULT AND DISCUSSION

Reflection Spectra Analysis

Average reflection of the top surface layer have decreased from 36% to 18% for nanocone textured CdTe TFSCs

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Optical Near-Field Enhancement

For Wavelength between 400-1100 nm

RESULT AND DISCUSSION

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MANUFACTURING FEASIBILITY

Fig: 45° angle-view SEM images of silicon nanocone arrays obtained by the wet anisotropic etching. [10]

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• This computational study aimed to improve the efficiency of CdTe thin-film/ultrathin film solar cells (TFSCs) by optimizing the surface texturing of the CdS window layer.

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• The CdTe TFSCs exhibit poor efficiency primarily attributed to substantial surface reflective losses.

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• One way of reducing surface reflective loss is via texturing the window layer (CdS) which also works to trap light within the absorber layer .

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• The calculated results indicated nanocone shaped surface texturing having a diameter, height and pitch of 600 nm, 400 nm and 75 nm respectively showed a 13.91% enhancement over the bare CdTe TFSC case.

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• The limitations of this study include lack of experimental verification of the simulation results. Such experimental verification would involve the fabrication of nanocone texturing to the CdS layer with controlled shapes and size.

CONCLUSION

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Future works will be focused on further improving CdTe TFSCs efficiency by incorporating other surface texturing techniques

FUTURE WORKS

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[1] David, L. et al. (2023) Thin-Film Solar Panels (2023 guide), EcoWatch. Available at: https://www.ecowatch.com/solar/thin-film-solar-panels.

[2] M. H. Weik, Fresnel reflection. Boston, MA: Springer US, 2001, pp. 657–657. [Online]. Available: https://doi.org/10.1007/1-4020-0613-6 7723

[3] V. Roshko, L. Kosyachenko, and E. Grushko, “Theoretical analysis of optical losses in cds/cdte solar cells,” Acta physica polonica A, vol. 120, no. 5, pp. 954–956, 2011.

[4] M. S. Kim, J. H. Lee, and M. K. Kwak, “Surface texturing methods for solar cell efficiency enhancement,” International Journal of Precision Engineering and Manufacturing, vol. 21, pp. 1389–1398, 2020.

[5] Thin-film solar panels, American Solar Energy Society. Available at: https://ases.org/thin-film-solar-panels.

[6] R. A. Rifat, N. Ibn Ashraf, S. A. Chowdhury, and M. H. Chowdhury, “The use of plasmonic metal nanoparticles to enhance the efficiency of thin-film silicon (SI) and gallium arsenide (GaAs) Solar Cells – A comparative study,” 2018 International Conference and Utility Exhibition on Green Energy for Sustainable Development (ICUE), 2018.

[7] J.-Y. Choi and C. B. Honsberg, “Reactive ion etching surface texturing of c-si using silica nanosphere lithography technique for solar cell application,” in 2013 IEEE 39th Photovoltaic Specialists Conference (PVSC). IEEE, 2013, pp. 1199–1202.

[8] Z. Wang, R. Zhang, S. Wang, M. Lu, X. Chen, Y. Zheng, L. Chen, Z. Ye, C. Wang, and K. Ho, “Broadband optical absorption by tunable Mie resonances in silicon nanocone arrays,” Scientific reports, vol. 5, no. 1, p. 7810, 2015.

[9] Y.-M. Chang, C.-L. Dai, T.-C. Cheng, and C.-W. Hsu, “Nanocone SiGe antireflective thin films fabricated by ultrahigh-vacuum chemical vapor deposition with in situ annealing,” Thin Solid Films, vol. 518, no. 14, pp. 3782–3785, 2010

[10] X. Liang et al., “Inverted silicon Nanopencil array solar cells with enhanced contact structures,” Scientific Reports, vol. 6, no. 1, 2016. doi:10.1038/srep34139

REFERENCES

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Co-Authors

MUSTAFA H. CHOWDHURY

Associate professor,

Department of EEE, IUB

Director, IUBPSL

Senior Member, IEEE

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ACKNOWLEDGMENT

The authors would like to acknowledge Independent University, Bangladesh (IUB) for funding this research (Research Project No: 2021-SETS-08) and providing other logistical support.

QUESTIONS?

IUB-PSL