Field-Effect Passivation of Undiffused Black Silicon Surfaces

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

doi:10.1109/jphotov.2021.3069124

Shaozhou Wang, Fa-Jun Ma + Show 4 more

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https://doi.org/10.1109/jphotov.2021.3069124

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Journal: IEEE Journal of Photovoltaics	Publication Date: Jul 1, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: UNSW Sydney

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 ( Q f ) 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 | Q f | up to 1 × 10 13 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 | Q f | up to ≈1 × 10 12 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 ( S eff ) is limited by minority carriers. This provides a possible solution for the empirical S eff ∝ 1/ Q f 4 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 (σ n / σ p ) is higher than 10 for p-type surfaces. For commonly used surface passivation films with a | Q f | larger than ≈1 × 10 12 cm -2 , there is little space charge compression for b-Si. Consequently, S eff simply scales with the surface area, i.e., there is no enhanced reduction of surface recombination by field-effect passivation on b-Si.

Highlights

L IGHT trapping and surface passivation are two important aspects of surface engineering for high-efficiency solar cells
We will discuss the main findings from our earlier work about the charge carrier population control resulting from space charge compression in 1-D, which is relevant for understanding the results in 2-D and 3-D
The characteristics of field-effect passivation on undiffused Black silicon (b-Si) surfaces under accumulation conditions have been investigated through 1-D/2-D/3-D wafer modeling using Sentaurus TCAD

Summary

Introduction

L IGHT trapping and surface passivation are two important aspects of surface engineering for high-efficiency solar cells. Black silicon (b-Si) is a textured surface with nanoscale high-aspect-ratio features. These nanofeatures contribute to the advanced light trapping, which can potentially realize highefficiency b-Si solar cells with near-zero reflectance [1], [2]. The surface area of b-Si is significantly larger than. Manuscript received March 2, 2021; revised March 17, 2021; accepted March 20, 2021. Date of publication April 19, 2021; date of current version June 21, 2021.

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