N.-P. Harder

University of Bern

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Rolf Brendel

Institut für Solarenergieforschung

Ralf Gogolin

Institut für Solarenergieforschung

Armin G. Aberle

National University of Singapore

R. Ferré

Institut für Solarenergieforschung

T. Neubert

Institut für Solarenergieforschung

Per I. Widenborg

National University of Singapore

Robby Peibst

Institut für Solarenergieforschung

Verena Mertens

Institut für Solarenergieforschung

Jan Schmidt

Leibniz University Hannover

P.P. Altermatt

Imperial College London

Cooperative Institutions

Institut für Solarenergieforschung

Fraunhofer Institute for Solar Energy Systems

Fraunhofer Society

UNSW Sydney

Leibniz University Hannover

Centre National de la Recherche Scientifique

Helmholtz-Zentrum Berlin für Materialien und Energie

Karlsruhe Institute of Technology

Laser Zentrum Hannover

ARC Centre of Excellence in Advanced Molecular Imaging

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Effect of SiO2 thicknesses in thermal-SiO2/PECVD-SiN stacks on surface passivation of n-type Cz silicon substrates

Ye. Larionova N.-P. Harder Rolf Brendel

The influence of SiO 2 thicknesses in thermal-SiO 2 /PECVD-SiN stacks on surface passivation of 2.5 Ωcm n-type Czochralski silicon substrates has been investigated. By annealing theses stacks in air we achieve surface recombination velocities (SRV) better (i.e. lower) than 2.6 cm/s for thin SiO 2 layers. We find a clear correlation between the thickness of the oxide layers and the annealing duration for obtaining optimum surface passivation. Furthermore, we also show that the absolute passivation quality of the SiO 2 /SiN stacks correlates to the SiO 2 thickness. We find that the SRV increases with increasing oxide thickness. We also present data of the surface passivation of these SiO 2 /SiN stacks after storage in the dark for several months. We find a slight degradation of the surface passivation for thicker oxides and no observable degradation for the 10 nm thick SiO 2 layer in our SiO 2 /SiN stacks after 6 weeks of storage. Short annealing at 400°C in air restores the passivation quality and from then on remains unchanged for the measured storage time of 35 weeks.

Passivation

10.1109/pvsc.2010.5614072

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Citations (1)

Silicon heterojunction solar cells: Influence of H2-dilution on cell performance

Solar Energy Materials and Solar Cells (2012)

Ralf Gogolin R. Ferré M. Turcu N.-P. Harder

Passivation

Carrier lifetime

Open-circuit voltage

10.1016/j.solmat.2012.06.001

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Citations (25)

Laser technology for solar cells and solar receivers

Aart Schoonderbeek Lars Richter Rainer Kling Andreas Ostendorf Berend Denkena

During the last few years, solar energy conversion by photovoltaics and solar receivers has grown enormously. For the future, efficient and durable products at low cost are necessary and laser technology offers many opportunities to realize this. Two of these technologies are discussed in this paper.First, a technology is discussed for producing solar receivers. A requirement for a solar receiver is a vacuum between the absorber and the cover glass tube during the operation lifetime of at least 25 years. To realize this requirement, glass and metal must be directly fused. A CO2-laser in combination with a process temperature controller is used instead of a gas flame to obtain a stable process and to avoid chemical interaction between flame and fusing zone. This paper shows the results of the developed laser process compared to a flame fusing process.The second technology discussed is used for producing silicon wafer based solar cells. A method to reduce costs is reducing the wafer thickness. Consequently, contact and pressure-free laser processing has large advantages. Experimental investigations are discussed for drilling holes for new solar cell concepts. Damage to the silicon around the processing area should be avoided. Results obtained with different laser types are compared regarding the quality, speed and costs.

10.2351/1.5061063

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Citations (1)

Thermophotonics

Semiconductor Science and Technology (2003)

N.-P. Harder P. Würfel Martin A. Green

Thermophotonics (TPX) is a recently proposed concept, which generalizes thermophotovoltaics (TPV) by allowing the radiation from the heat source to be increased by an internal electrochemical potential difference. This paper examines the basic working principle of TPX by means of detailed balance calculations. In these calculations TPX is not only modelled by the highly idealized standard Shockley–Queisser analysis but also in a more realistic manner, in which two typical parasitic loss mechanisms are included: (a) non-radiative recombination and (b) non-zero absorptivity/emissivity in the sub-bandgap energy spectrum. We show that TPX, in principle, allows a much higher rate of electrical power extraction from a heat source than TPV. When applying TPX to the conversion of solar energy we furthermore show that for a realistic absorber geometry TPX has a substantially higher theoretical conversion efficiency than TPV, particularly in the presence of parasitic sub-bandgap absorption/emission. Additionally, the range of suitable bandgap energies for TPX is greatly enhanced towards larger values over that of TPV. An essential requirement, however, is very high external electro-luminescent quantum efficiency.

Thermophotovoltaic

Molar absorptivity

Thermal Radiation

Quantum Efficiency

Detailed balance

Radiant energy

Energy transformation

10.1088/0268-1242/18/5/319

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Citations (75)

Comparison of ICP-AlOx and ALD-Al2O3 Layers for the Rear Surface Passivation of C-Si Solar Cells

Energy Procedia (2012)

Boris Veith Thorsten Dullweber Michael Siebert Christopher Kranz Florian Werner

The deposition rate of the standard (i.e. sequential) atomic layer deposition (ALD) process is very low compared to the plasma-enhanced chemical vapour deposition (PECVD) process. Therefore, as a short- and medium-term perspective, PECVD aluminium oxide (AlOx) films might be better suited for the implementation into industrial-type solar cells than ALD-Al2O3 films. In this paper, we report results achieved with a newly developed PECVD deposition process for AlOx using an inductively coupled plasma (ICP). We compare the results to high-quality ALD-Al2O3 films. We examine a stack consisting of a thin AlOx passivation layer and a PECVD silicon nitride (SiNy) capping layer. Surface recombination velocities below 9 cm/s were measured on low-resistivity (1.4 Ωcm) p-type crystalline silicon wafers passivated either by ICP-PECVD-AlOx films or by ALD-Al2O3 films after annealing at 425̊C. Both passivation schemes provide an excellent thermal stability during firing at 910̊C with SRVs below 12 cm/s for both, Al2O3/SiNy stacks and single Al2O3 layers. A fixed negative charge of −4×1012 cm−2 is measured for ICP-AlOx and ALD-Al2O3, whereas the interface state density is higher for the ICP-AlOx layer with values of 11.0×1011 eV−1cm−2 compared to 1.3×1011 eV−1cm−2 for ALD-Al2O3. Implemented into large-area screen-printed PERC solar cells, an independently confirmed efficiency of 20.1% for ICP-AlOx and an efficiency of 19.6% for ALD-Al2O3 are achieved.

Passivation

Aluminium oxides

10.1016/j.egypro.2012.07.080

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Citations (36)

Boron-Doped PECVD Silicon Oxides as Diffusion Sources for Simplified High-Efficiency Solar Cell Fabrication

World Conference on Photovoltaic Energy Conversion (2013)

Pietro P. Altermatt N.-P. Harder Bianca Lim Hannes Wagner G. Schraps

We develop plasma-deposited boron-doped silicon oxide layers with multifunctional capabilities: Firstly, they are used as local diffusion sources for attaining low saturation current densities of J0 = 84 fA/cm at sheet resistances as low as 67 /□ and surface boron concentrations in the range of 4–710 cm3, suitable for efficient metallization. Secondly, they act as diffusion barriers against other dopants. Therefore a co-diffusion process consisting of a boron drive-in and a phosphorus diffusion in a POCl3 furnace in only one high temperature step potentially allows to simplify the fabrication of high-efficiency n-type PERT cells. Process and device simulations indicate that a co-diffusion temperature near 900C and a co-diffusion time of about 20 minutes are optimum for reaching cell efficiencies near 21%.

Saturation current

BORO

10.4229/28theupvsec2013-2dv.3.52

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Citations (13)

New materials for optical thin films

Applied Optics (1976)

F. Stetter R. Esselborn N.-P. Harder Martin Friz P. Tolles

New materials for optical thin films are presented. Zirconium oxide, titanium oxide, ceric oxide, and hafnium oxide in the form of black tablets or cones of various sizes for the electron beam evaporation technique were developed. These materials are oxygen depleted and give an uniform melt during the evaporation to give reproducible evaporation characteristics. A new mixture consisting of ZrO2 and ZrTiO4 for the production of high index layers is described. The evaporation conditions of the substance and the properties of thin layers of the mixture are given. The refractive index is 2.15 at 500 nm. The transmittance range is 0.4–7 μm. The layers are optically homogeneous. The application of layers of this mixture in a three-layer antireflection coating is described.

Optical coating

10.1364/ao.15.002315

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Citations (37)

Dependence of the recombination in thin-film Si solar cells grown by ion-assisted deposition on the crystallographic orientation of the substrate

Solar Energy Materials and Solar Cells (2002)

Dirk Holger Neuhaus N.-P. Harder S. Oelting R.A. Bardos A.B. Sproul

Carrier lifetime

10.1016/s0927-0248(02)00078-8

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Citations (9)

Alba - Development of High-Efficiency Multi-Crystalline Si EWT Solar Cells for Industrial Fabrication at Q-Cells

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain (2008)

Stefan W. Glunz A. Grohe D. Kray Christian Schmiga N.-P. Harder

The goal of the project Alba is the development and fabrication of EWT solar cells on multi-crystalline silicon with a clearly increased cell efficiency compared to standard industrial Si cells. The project lays special focus on the development of industrially applicable processes. Exemplary realisation of advanced process steps for the fabrication of EWT cells which are suitable for mass production of high efficiency solar cells is shown in this paper. First results of the successful demonstration of the cell design on a laboratory scale are presented while the introduction of the cell concept into pilot production at Q-Cells's new Reiner Lemoine Research Centre is announced.

10.4229/23rdeupvsec2008-2ao.1.6

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Citations (3)

High Fill-Factors of Back-Junction Solar Cells without Front Surface Field Diffusion

World Conference on Photovoltaic Energy Conversion (2012)

N.-P. Harder P.P. Altermatt Robby Peibst Yevgeniya Larionova Udo Römer

We investigate by numerical simulations the influence of the front surface field (FSF) in high- efficiency interdigitated back contact (IBC) solar cells . It is often found that IBC cells with FSF show higher fill factors (FF) as compared to cells without FSF. By analyzing the local recombination currents we show that the major benefit of the FSF for the fill factor of IBC cells is not based on supplying lateral conductivity in the FSF. More important is that a diffused FSF ensures low level injection conditions at the surface. Recombination in low-level injection results in a lower ideality factor and therefore in higher FF as compared to recombination in high-level injection. Furthermore we show that the diffused FSF can be replaced by a sufficient amount of fixed charges at the surface without causing a decrease in FF. Fixed negative charges of front-side Al2O3 passivation create in low-injection an inversion layer at the surface of n-type solar cells and maintain the surface in low-injection even when the bulk enters high-injection. In addition the absence of the doped region at the front produces less Auger recombination compared to front sides with FSF. Consequently, Al2O3 front side passivation without FSF enables higher efficiencies compared to front surfaces with FSF.

Passivation

Auger effect

10.4229/27theupvsec2012-2do.3.5

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Citations (9)