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CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells

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posted on 13.07.2018, 09:02 by Drew E. Swanson, Carey Reich, Ali Abbas, Tushar M. Shimpi, Hanxiao Liu, Fernando A. Ponce, Michael Walls, Yong-Hang Zhang, Wyatt K. Metzger, Walajabad S. Sampath, Zachary C. Holman
© 2018 Author(s). As single-junction silicon solar cells approach their theoretical limits, tandems provide the primary path to higher efficiencies. CdTe alloys can be tuned with magnesium (CdMgTe) or zinc (CdZnTe) for ideal tandem pairing with silicon. A II-VI/Si tandem holds the greatest promise for inexpensive, high-efficiency top cells that can be quickly deployed in the market using existing polycrystalline CdTe manufacturing lines combined with mature silicon production lines. Currently, all high efficiency polycrystalline CdTe cells require a chloride-based passivation process to passivate grain boundaries and bulk defects. This research examines the rich chemistry and physics that has historically limited performance when extending Cl treatments to polycrystalline 1.7-eV CdMgTe and CdZnTe absorbers. A combination of transmittance, quantum efficiency, photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscopy clearly reveals that during passivation, Mg segregates and out-diffuses, initially at the grain boundaries but eventually throughout the bulk. CdZnTe exhibits similar Zn segregation behavior; however, the onset and progression is localized to the back of the device. After passivation, CdMgTe and CdZnTe can render a layer that is reduced to predominantly CdTe electro-optical behavior. Contact instabilities caused by inter-diffusion between the layers create additional complications. The results outline critical issues and paths for these materials to be successfully implemented in Si-based tandems and other applications.

Funding

This work was supported by DOE grant PVRD DE-EE0007552.

History

School

  • Mechanical, Electrical and Manufacturing Engineering

Published in

Journal of Applied Physics

Volume

123

Issue

20

Citation

SWANSON, D.E. ...et al., 2018. CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells. Journal of Applied Physics, 123: 203101.

Publisher

© The Authors. Published by AIP

Version

NA (Not Applicable or Unknown)

Acceptance date

30/04/2018

Publication date

2018

Notes

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in SWANSON, D.E. ...et al., 2018. CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells. Journal of Applied Physics, 123: 203101 and may be found at https://doi.org/10.1063/1.5023811

ISSN

0021-8979

eISSN

1089-7550

Language

en

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