Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system.

Shui-Yang Lien,Chih-Hsiang Yang,Chung-Yuan Kung,Kuei-Ching Wu

doi:10.1186/s11671-015-0803-9

Abstract

Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (Voc) and short-circuit current (Jsc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the Voc of 0.647 V, Jsc of 38.2 mA/cm2, fill factor of 0.776, and the efficiency of 19.18% can be achieved.

Highlights

For the past decade years, dielectric films have become promising materials applied in high-efficiency silicon solar cells due to their superior surface passivation effect
An attractive candidate for outstanding Si surface passivation is aluminum oxide (Al2O3), which can be deposited by physical vapor deposition (PVD) system [1], chemical vapor deposition (CVD) system [2,3,4], liquidphase deposition (LPD) technique [5,6], and atomic layer deposition (ALD) system [7,8,9]
It can be seen that under different deposition cycles, all the Al2O3 films are uniform without any rough morphology on the surface, revealing the feasibility and reproducibility of this ALD system

Summary

Introduction

For the past decade years, dielectric films have become promising materials applied in high-efficiency silicon solar cells due to their superior surface passivation effect. An attractive candidate for outstanding Si surface passivation is aluminum oxide (Al2O3), which can be deposited by physical vapor deposition (PVD) system [1], chemical vapor deposition (CVD) system [2,3,4], liquidphase deposition (LPD) technique [5,6], and atomic layer deposition (ALD) system [7,8,9]. ALD system is the most suitable choice for the deposition of Al2O3 owing to some advantages: (i) capable of producing very thin conformal and uniform films, (ii) with large process temperature window, and (iii) able to deposit films on high-aspect-ratio substrates. The deposition of Al2O3 for PERC is mainly by turn-key plasma-enhanced chemical vapor deposition (PECVD) technique due to its higher production capacity in comparison with ALD system.

Methods

Results

Conclusion