Abstract

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.

Original languageEnglish (US)
Article number203101
JournalJournal of Applied Physics
Volume123
Issue number20
DOIs
StatePublished - May 28 2018

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photovoltaic cells
passivity
absorbers
grain boundaries
silicon
cells
progressions
magnesium
quantum efficiency
transmittance
manufacturing
zinc
solar cells
chlorides
electron energy
chemistry
photoluminescence
transmission electron microscopy
physics
defects

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells. / Swanson, Drew E.; Reich, Carey; Abbas, Ali; Shimpi, Tushar; Liu, Hanxiao; Ponce, Fernando; Walls, John M.; Zhang, Yong-Hang; Metzger, Wyatt K.; Sampath, W. S.; Holman, Zachary.

In: Journal of Applied Physics, Vol. 123, No. 20, 203101, 28.05.2018.

Research output: Contribution to journalArticle

Swanson, DE, Reich, C, Abbas, A, Shimpi, T, Liu, H, Ponce, F, Walls, JM, Zhang, Y-H, Metzger, WK, Sampath, WS & Holman, Z 2018, 'CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells', Journal of Applied Physics, vol. 123, no. 20, 203101. https://doi.org/10.1063/1.5023811
Swanson, Drew E. ; Reich, Carey ; Abbas, Ali ; Shimpi, Tushar ; Liu, Hanxiao ; Ponce, Fernando ; Walls, John M. ; Zhang, Yong-Hang ; Metzger, Wyatt K. ; Sampath, W. S. ; Holman, Zachary. / CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells. In: Journal of Applied Physics. 2018 ; Vol. 123, No. 20.
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