Oxidation precursor dependence of atomic layer deposited Al2O3 films in a-Si:H(i)/Al2O3 surface passivation stacks.

Yuren Xiang,Endong Jia,Chunlan Zhou,Wenjing Wang

doi:10.1186/s11671-015-0798-2

Abstract

In order to obtain a good passivation of a silicon surface, more and more stack passivation schemes have been used in high-efficiency silicon solar cell fabrication. In this work, we prepared a-Si:H(i)/Al2O3 stacks on KOH solution-polished n-type solar grade mono-silicon(100) wafers. For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used. Interface trap density spectra were obtained for Si passivation with a-Si films and a-Si:H(i)/Al2O3 stacks by a non-contact corona C-V technique. After the fabrication of a-Si:H(i)/Al2O3 stacks, the minimum interface trap density was reduced from original 3 × 1012 to 1 × 1012 cm−2 eV−1, the surface total charge density increased by nearly one order of magnitude for PE-ALD samples and about 0.4 × 1012 cm−2 for a T-ALD sample, and the carrier lifetimes increased by a factor of three (from about 10 μs to about 30 μs). Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives. In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

Highlights

An excellent interface passivation has been considered as the key point for high-efficiency solar cells such as passivated emitter and rear cell (PERC), heterojunction with intrinsic thin layer (HIT) or interdigitated back contact (IBC) device structures
The TALD samples have higher effective minority carrier lifetimes just before deposition, but the advantage is lost after annealing contrasted with plasma enhanced atomic layer deposition (PE-atomic layer deposition (ALD)) samples, especially for the Al2O3 deposition at the low substrate temperature of 100°C
In this study, we demonstrated that the amorphous silicon (a-Si):H(i)/Al2O3 stack passivation layer can provide satisfactory passivation effect and thermal stability after annealing at 450°C for 10 min

Summary

Introduction

An excellent interface passivation has been considered as the key point for high-efficiency solar cells such as passivated emitter and rear cell (PERC), heterojunction with intrinsic thin layer (HIT) or interdigitated back contact (IBC) device structures. The properties of aluminum oxide (Al2O3) films and hydrogenated amorphous silicon (a-Si: H) films have been widely investigated for solar cell fabrication. Both of them have shown excellent performances, such as remarkable passivation behavior on both n- and p-type Si surfaces and the cost-saving deposition using atomic layer deposition (ALD) and plasma-enhanced vapor chemical deposition (PECVD) at low temperatures, respectively [1]. Various passivation stack schemes, such as SiO2/Al2O3, Al2O3/a-SiNx:H, a-Si:H/SiNx, etc., have already been investigated to improve the passivation effect, giving consideration to both low temperature deposition process and stability of thermal and ultraviolet (UV) radiation in the photovoltaic field [4,5,6,7].

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