Field-Effect Passivation of Undiffused Black Silicon Surfaces

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 4 f 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.

An Artificial-Intelligence-Assisted Investigation on the Potential of Black Silicon Nanotextures for Silicon Solar Cells

“…To investigate the electrical performance of featured b-Si textures via the comparison to the MT RPD reference, 2D process and 3D device simulations were conducted using Sentaurus TCAD. The textured devices were simulated by using the cylindrical coordinate and periodical boundary setting for unit devices to simplify the simulated structures . An identical POCl 3 diffusion simulation in p -type substrates with a 1.5 × 10 16 cm –3 doping level was conducted for all the texture conditions using a recipe from ref .…”

“…The textured devices were simulated by using the cylindrical coordinate and periodical boundary setting for unit devices to simplify the simulated structures. 16 An identical POCl 3 diffusion simulation in p-type substrates with a 1.5 × 10 16 cm −3 doping level was conducted for all the texture conditions using a recipe from ref 57. Interface recombination was simulated using Altermatt's dopant-dependent Si-SiO x parameterization model 58 for the intrinsic recombination velocity determination and assuming a strong field-effect passivation with an interface charge density of 5 × 10 12 cm −2 .…”

“…The b-Si surface morphology has a decisive influence on the solar cell performance, and it can be evaluated by two effective metrics. The lateral surface area-to-projected surface area ratio, or the enhanced area factor (EAF), is a widely used metric to quantify the relative surface area. − Another metric is the surface-to-volume ratio or specific surface area (SSA), which was recently proposed to quantify the size of b-Si nanofeatures. , The b-Si optical performance is usually evaluated by the weighted average reflectance (WAR) calculated by the wavelength-dependent photon flux under an AM1.5G spectrum condition from a wavelength range of around 300–1100 nm . Although the application of MCCE b-Si has been proven successful in the industry for multi-Si, the research on integrating b-Si into high-efficiency solar cells is still at a relatively early stage, i.e., most of the published scientific articles are using Aluminum Back Surface Field (Al-BSF) architectures (95 articles identified in this work), while there are only a few using Passivated Emitter and Rear Contact (PERC) architectures, − Interdigitated Back Contact (IBC) architectures, − Tunnel Oxide Passivated Contact (TOPCon) architectures, − and heterojunction (HJT) architectures. , Due to the limited b-Si research in advanced architectures, the solar cell efficiency records using b-Si are lagging compared to those using conventional textures.…”

Scanning Electron Microscopy Dopant Contrast Imaging of Phosphorus‐Diffused Silicon

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in surface nanotexturing or black silicon (BSi) technology show promise for enhancing the energy conversion efficiency of solar cells from the improved optical performance if other associated losses can be limited. [1][2][3][4][5][6][7][8] However, the integration of nanotextures into solar cells is complicated by its altered surface passivation [9] and dopant diffusion [10,11] behavior compared to planar or microtextured silicon. In particular, the spatial dopant distribution of n + BSi is challenging to characterize.

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