Florian Werner

University of Luxembourg

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Susanne Siebentritt

University of Luxembourg

Jan Schmidt

Leibniz University Hannover

Rolf Brendel

Institut für Solarenergieforschung

Michele Melchiorre

University of Luxembourg

Dimitri Zielke

Institut für Solarenergieforschung

Boris Veith

Institut für Solarenergieforschung

Finn Babbe

Joint Center for Artificial Photosynthesis

Hossam Elanzeery

University of Luxembourg

D. Korzec

University of Wuppertal

Mohit Sood

University of Luxembourg

Cooperative Institutions

University of Luxembourg

University of Göttingen

Luxembourg Institute of Science and Technology

Institut für Solarenergieforschung

Centre National de la Recherche Scientifique

Technical University of Munich

Helmholtz-Zentrum Berlin für Materialien und Energie

IMEC

Leibniz University Hannover

University of Cambridge

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Electronic and chemical properties of the c-Si/Al2O3 interface

Journal of Applied Physics (2011)

Florian Werner Boris Veith Dimitri Zielke L. Kühnemund Christoph Tegenkamp

Using aluminum oxide (Al2O3) films deposited by atomic layer deposition (ALD), the dominant passivation mechanisms at the c-Si/Al2O3 interface, as well as the chemical composition of the interface region, are investigated. The excellent surface passivation quality of thin Al2O3 films is predominantly assigned to a high negative fixed charge density of Qf = − (4 ± 1) × 1012 cm−2, which is located within 1nm of the Si/Al2O3 interface and is independent of the layer thickness. A deterioration of the passivation quality for ultrathin Al2O3 layers is explained by a strong increase in the interface state density, presumably due to an incomplete reaction of the trimethyl-aluminum (TMA) molecules during the first ALD cycles. A high oxygen-to-aluminum atomic ratio resulting from the incomplete adsorption of the TMA molecules is suggested as a possible source of the high negative charge density Qf at the Si/Al2O3 interface.

Passivation

Aluminum Oxide

Fixed charge

Deposition

Aluminium oxides

Charge density

10.1063/1.3587227

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Citations (225)

Advances in the Surface Passivation of Silicon Solar Cells

Energy Procedia (2012)

Jan Schmidt Florian Werner Boris Veith Dimitri Zielke S. Steingrube

The surface passivation properties of aluminium oxide (Al2O3) on crystalline Si are compared with the traditional passivation system of silicon nitride (SiNx). It is shown that Al2O3 has fundamental advantages over SiNx when applied to the rear of p-type silicon solar cells as well as to the p+ emitter of n-type silicon solar cells. Special emphasis is paid to the transfer of Al2O3 into industrial solar cell production. We compare different Al2O3 deposition techniques suitable for mass production such as ultrafast spatial atomic layer deposition, inline plasma-enhanced chemical vapour deposition and reactive sputtering. Finally, we review the most recent cell results with Al2O3 passivation and give a brief outlook on the future prospects of Al2O3 in silicon solar cell production.

Passivation

Deposition

10.1016/j.egypro.2012.02.004

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Citations (98)

Ultra-thin passivation layers in Cu(In,Ga)Se2 thin-film solar cells: full-area passivated front contacts and their impact on bulk doping

Scientific Reports (2020)

Florian Werner Boris Veith‐Wolf Michele Melchiorre Finn Babbe Jan Schmidt

Abstract In the search for highly transparent and non-toxic alternative front layers replacing state-of-the-art CdS in Cu(In,Ga)Se 2 thin-film solar cells, alternatives rarely exceed reference devices in terms of efficiency. Full-area ultra-thin aluminium oxide tunnelling layers do not require any contact patterning and thus overcome the main drawback of insulating passivation layers. Even a few monolayers of aluminium oxide can be deposited in a controlled manner by atomic layer deposition, they show excellent interface passivation properties, low absorption, and suitable current transport characteristics on test devices. Depositing a ZnO-based transparent front contact, however, results in extremely poor solar cell performance. The issue is not necessarily a low quality of the alternative front layer, but rather the intricate relation between front layer processing and electronic bulk properties in the absorber layer. We identify three challenges critical for the development of novel front passivation approaches: (i) both Cd and Zn impurities beneficially reduce the high native net dopant concentration in the space charge region, (ii) sputter deposition of ZnO damages the passivation layer resulting in increased interface recombination, (iii) thermal treatments of devices with ZnO layer result in substantial Zn diffusion, which can penetrate the full absorber thickness already at moderate temperatures.

Passivation

10.1038/s41598-020-64448-9

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3D stimulated Raman spectral imaging of water dynamics associated with pectin-glycocalyceal entanglement

Biomedical Optics Express (2023)

Moritz Floess Tobias Steinle Florian Werner Yunshan Wang Willi L. Wagner

Pectin is a heteropolysaccharide responsible for the structural integrity of the cell walls of terrestrial plants. When applied to the surface of mammalian visceral organs, pectin films form a strong physical bond with the surface glycocalyx. A potential mechanism of pectin adhesion to the glycocalyx is the water-dependent entanglement of pectin polysaccharide chains with the glycocalyx. A better understanding of such fundamental mechanisms regarding the water transport dynamics in pectin hydrogels is of importance for medical applications, e.g., surgical wound sealing. We report on the water transport dynamics in hydrating glass-phase pectin films with particular emphasis on the water content at the pectin-glycocalyceal interface. We used label-free 3D stimulated Raman scattering (SRS) spectral imaging to provide insights into the pectin-tissue adhesive interface without the confounding effects of sample fixation, dehydration, shrinkage, or staining.

Pectin

Glycocalyx

Water Transport

10.1364/boe.485314

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Interface recombination parameters of atomic-layer-deposited Al2O3 on crystalline silicon

Journal of Applied Physics (2012)

Florian Werner A. Cosceev Jan Schmidt

We measure the energy-dependent interface recombination parameters at the c-Si/Al2O3 interface using the frequency-dependent conductance technique. The hole capture cross section σp = (4 ± 3) × 10−16 cm2 is energy-independent, whereas the electron capture cross section σn shows a pronounced energy dependence and decreases from (7 ± 4) × 10−15 cm2 at midgap over two orders of magnitude toward the conduction band edge Ec. The capture cross section ratio at midgap is highly asymmetric with σn/σp = 5–70. The interface state density Dit is of the order of 1 × 1011 eV−1 cm−2 at midgap. Besides the main defect, a second type of defect with a capture cross section below 10−19 cm2 is resolved near the valence band edge. Numerical calculations of the injection-dependent effective surface recombination velocity using the measured interface recombination parameters show an excellent agreement with experimental data measured using the photoconductance technique.

Electron capture

10.1063/1.3700241

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Citations (40)

InN nanocolumns - electrical properties and site-selective growth

Verhandlungen der Deutschen Physikalischen Gesellschaft (2008)

Christian Denker F. Limbach Soenke Huels Florian Werner J. Malindretos

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Mycorrhiza Networks Promote Biodiversity and Stabilize the Tropical Mountain Rain Forest Ecosystem: Perspectives for Understanding Complex Communities

Ecological studies (2013)

Ingrid Kottke Sabrina Setaro Ingeborg Haug Paulo Herrera Darío Cruz

Nestedness

Orchidaceae

Epiphyte

Glomeromycota

10.1007/978-3-642-38137-9_14

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Citations (30)

Doping mechanism in pure CuInSe2

Journal of Applied Physics (2016)

Florian Werner Diego Colombara Michele Melchiorre Nathalie Valle Brahime El Adib

We investigate the dopant concentration and majority carrier mobility in epitaxial CuInSe2 thin films for different copper-to-indium ratios and selenium excess during growth. We find that all copper-poor samples are n-type, and that hopping conduction in a shallow donor state plays a significant role for carrier transport. Annealing in sodium ambient enhances gallium in-diffusion from the substrate wafer and changes the net doping of the previously n-type samples to p-type. We suggest that sodium incorporation from the glass might be responsible for the observed p-type doping in polycrystalline Cu-poor CuInSe2 solar cell absorbers.

Carrier lifetime

10.1063/1.4947585

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Citations (27)

Influence of Conduction Band Offsets at Window/Buffer and Buffer/Absorber Interfaces on the Roll-Over of J-V Curves of CIGS Solar Cells

2017 IEEE 44th Photovoltaic Specialist Conference (PVSC) (2017)

Giovanna Sozzi Simone Di Napoli R. Menozzi Florian Werner Susanne Siebentritt

By comparing simulated and measured current-voltage (J-V) characteristics of a high efficiency Cu(In,Ga)Se ₂ (CIGS) solar cell, we investigate the effect of conduction band offsets at window/buffer and buffer/absorber interfaces on the roll-over of the J-V curves with temperature. We simulate the J-V characteristics in the temperature range 300 K - 100 K, achieving good fits with measurements by describing the transport of electrons over the barrier at the ZnO/CdS interface by the thermionic-emission theory, and including a Schottky contact at the back CIGS/Mo interface.

Thermionic emission

Buffer (optical fiber)

Schottky effect

10.1109/pvsc.2017.8366649

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Improved quantitative description of Auger recombination in crystalline silicon

Physical Review B (2012)

Armin Richter Stefan W. Glunz Florian Werner Jan Schmidt Andrés Cuevas

An accurate quantitative description of the Auger recombination rate in silicon as a function of the dopant density and the carrier injection level is important to understand the physics of this fundamental mechanism and to predict the physical limits to the performance of silicon based devices. Technological progress has permitted a near suppression of competing recombination mechanisms, both in the bulk of the silicon crystal and at the surfaces. This, coupled with advanced characterization techniques, has led to an improved determination of the Auger recombination rate, which is lower than previously thought. In this contribution we present a systematic study of the injection-dependent carrier recombination for a broad range of dopant concentrations of high-purity $n$-type and $p$-type silicon wafers passivated with state-of-the-art dielectric layers of aluminum oxide or silicon nitride. Based on these measurements, we develop a general parametrization for intrinsic recombination in crystalline silicon at 300 K consistent with the theory of Coulomb-enhanced Auger and radiative recombination. Based on this improved description we are able to analyze physical aspects of the Auger recombination mechanism such as the Coulomb enhancement.

Auger effect

Carrier lifetime

10.1103/physrevb.86.165202

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Citations (803)