Aline Vanderhaegen

University of Luxembourg

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Daniele Brida

University of Luxembourg

Markus Ludwig

Deutsches Elektronen-Synchrotron DESY

Kilian R. Keller

University of Luxembourg

Mohit Sood

University of Luxembourg

Susanne Siebentritt

University of Luxembourg

Thomas Deckert

University of Luxembourg

Ricardo Rojas‐Aedo

University of Luxembourg

Thomas Paul Weiss

University of Luxembourg

Tobias Törndahl

Uppsala University

Damilola Adeleye

University of Luxembourg

Cooperative Institutions

University of Luxembourg

Uppsala University

Luxembourg Institute of Science and Technology

University of Cambridge

University of Konstanz

Sacred Heart University

University of Strathclyde

National Institute of Advanced Industrial Science and Technology

Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute

Linköping University

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CuIn(Se,Te)2 absorbers with bandgaps < 1 eV for bottom cells in tandem applications

arXiv (Cornell University) (2023)

Thomas Paul Weiss Mohit Sood Aline Vanderhaegen Susanne Siebentritt

Thin-film solar cells reach high efficiencies and have a low carbon footprint in production. Tandem solar cells have the potential to significantly increase the efficiency of this technology, where the bottom-cell is generally composed of a Cu(In,Ga)Se2 absorber layer with bandgaps around 1 eV or higher. Here, we investigate CuIn(Se1-xTex)2 absorber layers and solar cells with bandgaps below 1 eV, which will bring the benefit of an additional degree of freedom for designing current-matched 2-terminal tandem devices. We report that CuIn(Se1-xTex)2 thin films can be grown single phase by co-evaporation and that the bandgap can be reduced to the optimum range for a bottom cell (0.92 - 0.95 eV). From photoluminescence spectroscopy it is found that no additional non-radiative losses are introduced to the absorber. However, Voc losses occur in the final solar cell due to non-optimised interfaces. Nevertheless, a record device with 9 % power conversion efficiency is demonstrated with a bandgap of 0.96 eV and x=0.15. Interface recombination is identified as a major recombination channel for larger Te contents. Thus, further efficiency improvements are anticipated for improved absorber/buffer interfaces.

Tandem

10.48550/arxiv.2308.16103

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Stable supercontinuum generation in water at high repetition rates

Aline Vanderhaegen Kilian R. Keller R. Rojas-Aedo Markus Ludwig Daniele Brida

Water is an effective nonlinear medium for supercontinuum (SC) generation. We demonstrate high SC signal stability through precise liquid velocity control and superior spectral broadening compared to established solids at multi-kilohertz (kHz) repetition rates.

Supercontinuum

Repetition (rhetorical device)

10.1364/cleo_si.2024.sth1c.6

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High stability white light generation in water at multi-kilohertz repetition rates

Optics Express (2023)

Kilian R. Keller Ricardo Rojas‐Aedo Aline Vanderhaegen Markus Ludwig Daniele Brida

An efficient supercontinuum (SC) generation featuring high spectral intensity across a large bandwidth requires high peak powers of several megawatts from pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition rates, the SC generated in most materials is unstable due to thermal effects. In this work, we leverage the superior dispersion properties of water to maximize the spectral width of the SC, while avoiding stability issues due to thermal loading by means of a constant laminar flow of the liquid. This flow is controlled by a differential pressure scheme that allows to precisely adjust the fluid velocity to an optimum value for maximum stability of the SC. This approach is successfully implemented for repetition rates of 50 kHz and 100 kHz and two different pump wavelengths in the visible (VIS) and near infrared (NIR) spectral region with stability of the SC signal only limited by the driving pulses. The resulting water SC spans more than one octave covering the VIS to NIR range. Compared to established materials, such as yttrium aluminum garnet (YAG) and sapphire, the spectral bandwidth is increased by 60% and 40% respectively. Our scheme has the potential to be implemented with other liquids such as bromine or carbon disulfide (CS2), which promise even wider broadening and operation up to the mid-infrared.

Repetition (rhetorical device)

10.1364/oe.503172

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Sub-8-fs Pulses in the Visible to Near Infrared from a Degenerate Optical Parametric Amplifier

Thomas Deckert Aline Vanderhaegen Daniele Brida

A single-stage optical parametric amplifier (OPA) operating at degeneracy delivers sub-8-fs pulses with excellent shot-to-shot stability. It complements the existing array of OPAs in the visible to near infrared for advanced multidimensional spectroscopy.

Optical parametric amplifier

Parametric oscillator

10.1364/cleo_si.2024.sw3a.3

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Mitigation of Phase Separation in High Ga Cu(In,Ga)S2 Absorbers to Achieve ∼ 1 Volt 15.6% Power Conversion Efficiency

Damilola Adeleye Mohit Sood Tobias Törndahl Adam Hultqvist Aline Vanderhaegen

The use of Cu(In,Ga)S2 as a top cell in tandem solar cell, despite having suitable properties for such an application, is hampered by a high open-circuit voltage (VOC) deficit. The deficit arises from a poor optoelectronic quality of the absorbers - engendered by phase separation - and the inadequate translation of the optoelectronic quality of the absorber into device VOC. In this work, we report the role of first stage substrate temperature in the mitigation of phase separation and optimized Cu-excess during growth in Cu(In,Ga)S2, which leads to reduced VOC deficit, resulting in a device with 15.6 % PCE with a VOC of ∼ 981 mV when completed with atomic layer deposited (Zn,Sn)O and Al:ZnMgO transparent conductive oxide.

Tandem

Open-circuit voltage

10.1109/pvsc48320.2023.10359848

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Sub-8 fs Pulses in the Visible to Near Infrared from a Single Stage Degenerate Optical Parametric Amplifier

Thomas Deckert Aline Vanderhaegen Daniele Brida

A single-stage degenerate optical parametric amplifier (DOPA) with broad amplification bandwidth produces sub-10 femtosecond pulses with excellent shot-to-shot stability. It complements the existing array of OPAs in the visible to near infrared for advanced spectroscopy.

Optical parametric amplifier

Parametric oscillator

Single stage

10.1109/cleo/europe-eqec57999.2023.10231610

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Wide‐Bandgap Cu(In, Ga)S₂ Solar Cell: Mitigation of Composition Segregation in High Ga Films for Better Efficiency

Small (2025)

Damilola Adeleye Mohit Sood Arivazhagan Valluvar Oli Tobias Törndahl Adam Hultqvist

Abstract Cu(In, Ga)S 2 demonstrates potential as a top cell material for tandem solar cells. However, achieving high efficiencies has been impeded by open‐circuit voltage (V OC ) deficits arising from In‐rich and Ga‐rich composition segregation in the absorber layer. This study presents a significant improvement in the optoelectronic quality of Cu(In, Ga)S 2 films through the mitigation of composition segregation in three‐stage co‐evaporated films. By elevating the substrate temperature during the first stage, the intermixing of In and Ga is promoted, leading to reduced Cu(In, Ga)S 2 composition segregation. Furthermore, the optimization of Cu‐excess during the second stage minimizes non‐radiative voltage loss. These combined strategies yield quasi‐Fermi level splitting exceeding 1 eV and a record V OC of 981 mV in Cu(In, Ga)S 2 devices. Consequently, a champion device achieves an in‐house power conversion efficiency (PCE) of 16.1% (active area) and a certified PCE of 14.8%, highlighting the potential of Cu(In, Ga)S 2 as a stable and efficient top‐cell device for tandem photovoltaics.

Tandem

Open-circuit voltage

10.1002/smll.202405221

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Water-based high stability supercontinuum generation at multi-kilohertz repetition rates

Kilian R. Keller Ricardo Rojas‐Aedo Aline Vanderhaegen Markus Ludwig Daniele Brida

In this work, we introduce a technical approach to harness liquids for highly stable and efficient Supercontinuum Generation (SCG) at up to few hundreds of kHz. Using a differential pressure scheme, the velocity at which the liquid interacting with the laser is exchanged, is optimized to achieve pump source limited stability. This approach is validated by generating a SC in water pumped at the Fundamental Wavelength (FW) and the Second Harmonic (SH) of a Yb:KGW laser amplifier at 50 kHz and 100 kHz. In addition to its high stability, the resulting SC signal is more broadband and has a higher spectral intensity compared to the signals obtained with the established crystals Yttrium Aluminum Garnat (YAG) and sapphire.

Supercontinuum

SIGNAL (programming language)

Ytterbium

10.1117/12.3022509

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High stability white light generation in water at multi-kilohertz repetition rate

arXiv (Cornell University) (2023)

Kilian R. Keller Ricardo Rojas‐Aedo Aline Vanderhaegen Markus Ludwig Daniele Brida

Efficient supercontinuum (SC) generation featuring high spectral intensity across a large bandwidth requires high peak powers of several megawatt from pulsed lasers. Under these conditions and at multi-kilohertz (kHz) repetition rates, the SC generated in most materials is unstable due to thermal effects. In this work, we leverage the superior dispersion properties of water to maximize the spectral width of the SC, while avoiding stability issues due to thermal loading by means of a constant laminar flow of the liquid. This flow is controlled by a differential pressure scheme that allows to precisely adjust the fluid velocity to an optimum value for maximum stability of the SC. This approach is successfully implemented for repetition rates of 50 kHz and 100 kHz and two different pump wavelengths in the visible (VIS) and near infrared (NIR) spectral region with stability of the SC signal only limited by the driving pulses. The resulting water SC spans more than one octave covering the VIS to NIR range. Compared to established materials, such as yttrium aluminum garnet (YAG) and sapphire, the spectral bandwidth is increased by 60 % and 40 % respectively. Our scheme has the potential to be implemented with other liquids such as bromine or carbon disulfide (CS2), which promise even wider broadening and operation up to the mid-infrared.

Supercontinuum

10.48550/arxiv.2308.06636

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Sub-8-fs pulses in the visible to near-infrared by a degenerate optical parametric amplifier

Optics Letters (2023)

Thomas Deckert Aline Vanderhaegen Daniele Brida

This work presents a single-stage optical parametric amplifier (OPA) operating at degeneracy (DOPA) and pumped by the third harmonic of a Yb:KGW laser system. This DOPA exploits the broad amplification bandwidth that occurs with type-I phase-matching in β-barium borate (BBO) when signal and idler overlap in the spectrum. The output pulses span from 590 to 780 nm (1.59-2.10 eV) with 7.75-fs duration after compression. Ultrashort pulses with similar bandwidths in this spectral window complement the existing array of optical parametric amplifiers that cover either the visible or the near-IR spectral regions with sub-10-fs pulses. This source of ultrashort optical pulses will enable the application of sophisticated spectroscopy techniques to the study of electronic coherences and energy migration pathways in biological, chemical, and condensed matter systems.

Optical parametric amplifier

10.1364/ol.498291

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Citations (8)