Field-effect passivation of undiffused black silicon surfaces

Shaozhou Wang, Xinyuan Wu, Fa-Jun Ma, David Payne, Malcolm Abbott, Bram Hoex

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Abstract

Black silicon (b-Si) surfaces typically have a high density of extreme nanofeatures and a significantly large surface area. This makes high-quality surface passivation even more critical for devices such as solar cells with b-Si surfaces. It has been hypothesized that conformal dielectrics with a high fixed charge density ( Qf ) are preferred as the nanoscale features of b-Si result in a significant enhancement of field-effect passivation. This article uses 1-D, 2-D, and 3-D numerical simulations to study surface passivation of b-Si, where we particularly focus on the charge carrier control by | Qf | up to 1 × 1013  cm−2 under accumulation conditions. We will show that there is a significant space charge region compression in b-Si nanofeatures, which affects the charge carrier population control for moderate | Qf | up to ≈1 × 1012  cm−2 . The average surface minority charge carrier density can be reduced by 70% in some cases, resulting in an equivalent reduction in area-normalized surface recombination losses if the effective surface recombination velocity ( Seff ) is limited by minority carriers. This provides a possible solution for the empirical Seff∝1/Q4f reported previously. We will also show that the situation is more complicated for surface passivation films where the ratio between the electron and hole capture cross section ( σn / σp ) is higher than 10 for p-type surfaces. For commonly used surface passivation films with a | Qf | larger than ≈1 × 1012  cm−2 , there is little space charge compression for b-Si. Consequently, Seff simply scales with the surface area, i.e., there is no enhanced reduction of surface recombination by field-effect passivation on b-Si.

Original languageEnglish
Pages (from-to)897-907
Number of pages11
JournalIEEE Journal of Photovoltaics
Volume11
Issue number4
DOIs
Publication statusPublished - Jul 2021

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