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

Journal article

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 (SiN_x) nanolayers with electronic properties suitable for effective hole-selective contacts. We use x-ray photoemission methods to investigate ultra-thin SiN_x grown via atomic layer deposition, and we find that the band alignment determined at the SiN_x/Si interface favors hole transport. A band offset ratio, ΔE_C/ΔE_V, of 1.62 ± 0.24 is found at the SiN_x/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 ΔE_C/ΔE_V ratio to 1.22 ± 0.18. The SiN_x/Si interface band alignment makes SiN_x nanolayers a promising architecture to achieve widely sought hole-selective passivating contacts for high efficiency silicon solar cells.

Authors: Khorani, E; McNab, S; Scheul, TE; Rahman, T; Bonilla, RS

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: AIP Publishing
• Journal: APL Materials
• Volume: 8
• Issue: 11
• Article number: 111106
• Publication date: 2020-11-05
• Acceptance date: 2020-10-21
• DOI: 10.1063/5.0023336
• EISSN: 2166-532X
• Language: English
• Keywords: FFR