Heikkinen, I T S; Koutsourakis, G; Virtanen, S; Yli-Koski, M; Wood, S; Vähänissi, V; Salmi, E; Castro, F A; Savin, H (2020) AlOx surface passivation of black silicon by spatial ALD: Stability under light soaking and damp heat exposure. Journal of Vacuum Science & Technology A, 38 (2). 022401 ISSN 0734-2101

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Abstract

Scientific breakthroughs in silicon surface passivation have enabled commercial high-efficiency photovoltaic devices making use of the black silicon nanostructure. In this study, we report on factors that influence the passivation stability of black silicon realized with industrially viable Spatial Atomic Layer Deposited (SALD) aluminum oxide (AlOx) under damp heat exposure and light soaking. Damp heat exposure conditions are 85°C and 85% relative humidity, and light soaking is performed with 0.6 Sun illumination at 75°C. It is demonstrated that reasonably thick (20 nm) passivation films are required for both black and planar surfaces in order to provide stable surface passivation over a period of 1000 h under both testing conditions. Both surface textures degrade at similar rates with 5 nm and 2 nm thick films. The mechanism for the passivation degradation is found to be different for damp heat exposure and light soaking. During damp heat exposure, the fixed charge density of AlOx is reduced, which decreases the amount of field-effect passivation. Degradation under light soaking, on the other hand, is likely to be related to the interface between silicon and the passivating film. Finally, a thin chemically-grown SiOx layer at the interface between the AlOx film and the silicon surface is shown to significantly increase the passivation stability under both light soaking and damp heat exposure. The results of this study provide valuable insights on surface passivation degradation mechanisms on nanostructured silicon surfaces, and pave the way for the industrial production of highly stable black silicon devices.

Item Type:	Article
Notes:	This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Vacuum Science & Technology A, (2020), 38(2) 022401 and may be found at https://doi.org/10.1116/1.5133896.
Keywords:	spatial atomic layer deposition, aluminum oxide, light soaking, damp heat exposure, surface passivation stability
Subjects:	Advanced Materials > Photovoltaics
Divisions:	Electromagnetic & Electrochemical Technologies
Identification number/DOI:	10.1116/1.5133896
Last Modified:	21 Apr 2021 10:54
URI:	http://eprintspublications.npl.co.uk/id/eprint/8722

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