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Optoelectronic properties of ultrathin ALD silicon nitride and its potential as a hole-selective nanolayer for high efficiency solar cells

Optoelectronic properties of ultrathin ALD silicon nitride and its potential as a hole-selective nanolayer for high efficiency solar cells
Optoelectronic properties of ultrathin ALD silicon nitride and its potential as a hole-selective nanolayer for high efficiency solar cells
Fully exploiting the power conversion efficiency limit of silicon solar cells requires the use of passivating contacts that minimize electrical losses at metal/silicon interfaces. An efficient hole-selective passivating contact remains one of the key challenges for this technology to be deployed industrially and to pave the way for adoption in tandem configurations. Here, we report the first account of silicon nitride (SiNx) nanolayers with electronic properties suitable for effective hole-selective contacts. We use x-ray photoemission methods to investigate ultra-thin SiNx grown via atomic layer deposition, and we find that the band alignment determined at the SiNx/Si interface favors hole transport. A band offset ratio, ΔEC/ΔEV, of 1.62 ± 0.24 is found at the SiNx/Si interface for the as-grown films. This equates to a 500-fold increase in tunneling selectivity for holes over electrons, for a film thickness of 3 nm. However, the thickness of such films increases by 2 Å–5 Å within 48 h in cleanroom conditions, which leads to a reduction in hole-selectivity. X-ray photoelectron spectroscopy depth profiling has shown this film growth to be linked to oxidation, and furthermore, it alters the ΔEC/ΔEV ratio to 1.22 ± 0.18. The SiNx/Si interface band alignment makes SiNx nanolayers a promising architecture to achieve widely sought hole-selective passivating contacts for high efficiency silicon solar cells.
2166-532X
Khorani, Edris
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McNab, Shona
8efe75ee-d03f-4976-b8da-70d3fd106036
Scheul, Tudor Emilian
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Rahman, Tasmiat
e7432efa-2683-484d-9ec6-2f9c568d30cd
Bonilla, Ruy Sebastian
f98fe8c5-7ac2-4e03-adaf-826a646a26ae
Boden, Stuart
83976b65-e90f-42d1-9a01-fe9cfc571bf8
Wilshaw, Peter
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Khorani, Edris
bbdfbcc3-5dd0-4a73-80ed-7a0bff1d5388
McNab, Shona
8efe75ee-d03f-4976-b8da-70d3fd106036
Scheul, Tudor Emilian
daf1d539-813a-4f66-b2c1-86f7e91fde8c
Rahman, Tasmiat
e7432efa-2683-484d-9ec6-2f9c568d30cd
Bonilla, Ruy Sebastian
f98fe8c5-7ac2-4e03-adaf-826a646a26ae
Boden, Stuart
83976b65-e90f-42d1-9a01-fe9cfc571bf8
Wilshaw, Peter
6cf4b05e-2f21-4451-85f1-7a1d88496cff

Khorani, Edris, McNab, Shona, Scheul, Tudor Emilian, Rahman, Tasmiat, Bonilla, Ruy Sebastian, Boden, Stuart and Wilshaw, Peter (2020) Optoelectronic properties of ultrathin ALD silicon nitride and its potential as a hole-selective nanolayer for high efficiency solar cells. APL Materials, 8 (11), [111106]. (doi:10.1063/5.0023336).

Record type: Article

Abstract

Fully exploiting the power conversion efficiency limit of silicon solar cells requires the use of passivating contacts that minimize electrical losses at metal/silicon interfaces. An efficient hole-selective passivating contact remains one of the key challenges for this technology to be deployed industrially and to pave the way for adoption in tandem configurations. Here, we report the first account of silicon nitride (SiNx) nanolayers with electronic properties suitable for effective hole-selective contacts. We use x-ray photoemission methods to investigate ultra-thin SiNx grown via atomic layer deposition, and we find that the band alignment determined at the SiNx/Si interface favors hole transport. A band offset ratio, ΔEC/ΔEV, of 1.62 ± 0.24 is found at the SiNx/Si interface for the as-grown films. This equates to a 500-fold increase in tunneling selectivity for holes over electrons, for a film thickness of 3 nm. However, the thickness of such films increases by 2 Å–5 Å within 48 h in cleanroom conditions, which leads to a reduction in hole-selectivity. X-ray photoelectron spectroscopy depth profiling has shown this film growth to be linked to oxidation, and furthermore, it alters the ΔEC/ΔEV ratio to 1.22 ± 0.18. The SiNx/Si interface band alignment makes SiNx nanolayers a promising architecture to achieve widely sought hole-selective passivating contacts for high efficiency silicon solar cells.

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Accepted/In Press date: 21 October 2020
e-pub ahead of print date: 5 November 2020
Published date: November 2020

Identifiers

Local EPrints ID: 444847
URI: http://eprints.soton.ac.uk/id/eprint/444847
ISSN: 2166-532X
PURE UUID: 8f277ae4-f9fb-42f2-a350-3edc2b51fd19
ORCID for Tudor Emilian Scheul: ORCID iD orcid.org/0000-0003-4517-6096
ORCID for Stuart Boden: ORCID iD orcid.org/0000-0002-4232-1828

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Date deposited: 06 Nov 2020 17:31
Last modified: 06 Nov 2020 17:33

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