The Influence of Orientation and Morphology on the Passivation of Crystalline Silicon Surfaces by Al2O3

Black, Lachlan E.; Kho, Teng; McIntosh, Keith R.; Cuevas, Andrés

doi:10.1016/j.egypro.2014.08.055

Cited by 15 publications

(5 citation statements)

References 16 publications

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“…Unlike [209] we are able to obtain clear results in this respect. This work was previously published in [210].…”

Section: Recombination At 100 111 and Textured Surfacesmentioning

confidence: 99%

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Black

2016

Springer Theses

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High-efficiency crystalline silicon solar cells must suppress recombination at their p-type surfaces. Thin-film, amorphous aluminium oxide (Al 2 O 3) has been shown to provide very effective passivation of such surfaces, assisted by its negative fixed charge. However, many details of Al 2 O 3 passivation remain poorly understood. Furthermore, conventional means of depositing passivating Al 2 O 3 are too slow or too expensive to be suitable for high-volume commercial production. This thesis addresses these issues in three ways: 1) by contributing to a deeper understanding of semiconductor-dielectric interfaces and semiconductor surface recombination mechanisms in general, 2) by investigating the properties of Al 2 O 3 as a passivating dielectric for silicon surfaces, and 3) by demonstrating the viability of APCVD as a high-throughput, industrially compatible deposition method for Al 2 O 3 , enabling its application to commercial solar cells. Using Al 2 O 3 as a test case, it is shown how a novel analysis of the extended conductance method can be used to i) distinguish the separate contributions to the interface state distribution at a semiconductor-dielectric interface, and ii) determine their capture cross-sections for both minority and majority carriers. Furthermore, the direct link between these measured interface state properties and the recombination rate at the semiconductor surface is experimentally demonstrated by showing that the former can be used to accurately predict the latter. Investigations of the surface passivation properties of Al 2 O 3 reveal a remarkably consistent picture. It is shown that the properties of the Si-Al 2 O 3 interface states are essentially independent of the Al 2 O 3 deposition conditions and technique. The interface properties are found to be independent of the surface dopant concentration at boron-and phosphorus-doped surfaces, while recombination is shown to be only weakly dependent on surface orientation and morphology as a result of the remarkable orientation-independence of the Si-Al 2 O 3 interface state properties. Meanwhile, the chemical origin of the charge at the Si-Al 2 O 3 interface is elucidated by correlating FTIR and electrical measurements. xi xii APCVD is clearly shown-for the first time-to be capable of depositing Al 2 O 3 films with exceptional surface passivation properties, comparable to the best results achieved using other deposition techniques. In the best case, interface state densities as low as 5 × 10 10 eV −1 cm −2 at midgap, and negative fixed charge concentrations of 3.3 × 10 12 cm −2 are measured, resulting in a saturation current density of 7 fA cm −2 on undiffused p-type surfaces. The APCVD films are shown to be thermally stable under standard solar cell processing conditions and are demonstrated in large-area solar cells with peak efficiencies of 21.3 %. These results demonstrate the viability of APCVD Al 2 O 3 as a surface passivation layer for industrial silicon solar cells.

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“…Unlike [209] we are able to obtain clear results in this respect. This work was previously published in [210].…”

Section: Recombination At 100 111 and Textured Surfacesmentioning

confidence: 99%

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Black

2016

Springer Theses

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“…First of all, the different crystal orientation ( 111 for textured versus 100 for polished) enhances recombination intrinsically because of the higher amount of dangling bonds in 111 surfaces compared with 100 surfaces. As a reference, the J 0e ratio between polished 111 and 100 surfaces (J 0e,pol 111 /J 0e,pol 100 ) has been estimated to be around 1-1.2 for annealed APCVD Al 2 O 3 layers [38]. Another potential factor, which is particularly difficult to quantify, is the existence of additional defects associated with enhanced stress at the edges and vertices of the pyramidal structure [39].…”

Section: B Impact Of Back-end Processing On Al 2 O 3 /Sio X Passivationmentioning

confidence: 99%

“…In addition, the Auger contribution could be slightly higher at textured surfaces than planar surfaces because of increased doping at pyramidal tips [40]. These additional factors can be encompassed in the J 0e ratio between textured 111 and polished 111 surfaces (J 0e,text 111 /J 0e,pol 111 ), which was estimated to be around 2.2-2.6 for APCVD Al 2 O 3 layers [38] and, hence, suggests that these additional effects are more relevant than the impact of surface orientation.…”

Section: B Impact Of Back-end Processing On Al 2 O 3 /Sio X Passivationmentioning

confidence: 99%

Large-Area n-Type PERT Solar Cells Featuring Rear p⁺ Emitter Passivated by ALD Al₂O₃

Cornagliotti

Urueña

Aleman

et al. 2015

IEEE J. Photovoltaics

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We present large-area n-type PERT solar cells featuring a rear boron emitter passivated by a stack of ALD Al 2 O 3 and PECVD SiO x . After illustrating the technological and fundamental advantages of such a device architecture, we show that the Al 2 O 3 /SiO x stack employed to passivate the boron emitter is unaffected by the rear metallization processes and can suppress the Shockley-Read-Hall surface recombination current to values below 2 fA/cm 2 , provided that the Al 2 O 3 thickness is larger than 7 nm. Efficiencies of 21.5% on 156-mm commercial-grade Cz-Si substrates are demonstrated in this study, when the rear Al 2 O 3 /SiO x passivation is applied in combination with a homogeneous front-surface field (FSF). The passivation stack developed herein can sustain cell efficiencies in excess of 22% and V o c above 685 mV when a selective FSF is implemented, despite the absence of passivated contacts. Finally, we demonstrate that such cells do not suffer from light-induced degradation.

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“…In order to overcome this, Al 2 O 3 coating can be used as the protective material for silicon [6][7][8][9][10][11][12][13][14][15][16]. The porous silicon can be prepared by conventional electrochemical anodization using silicon wafer as a working electrode.…”

Section: Introductionmentioning

confidence: 99%

Structural and morphological characterization of Al2O3 coated macro-porous silicon by atomic layer deposition

et al. 2016

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The Influence of Orientation and Morphology on the Passivation of Crystalline Silicon Surfaces by Al2O3

Cited by 15 publications

References 16 publications

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Large-Area n-Type PERT Solar Cells Featuring Rear p⁺ Emitter Passivated by ALD Al₂O₃

Structural and morphological characterization of Al2O3 coated macro-porous silicon by atomic layer deposition

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The Influence of Orientation and Morphology on the Passivation of Crystalline Silicon Surfaces by Al2O3

Cited by 15 publications

References 16 publications

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Large-Area n-Type PERT Solar Cells Featuring Rear p+ Emitter Passivated by ALD Al2 O3

Structural and morphological characterization of Al2O3 coated macro-porous silicon by atomic layer deposition

Contact Info

Product

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Large-Area n-Type PERT Solar Cells Featuring Rear p⁺ Emitter Passivated by ALD Al₂O₃