References of "Redinger, Alex 50026033"
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See detailPassivation of the CuInSe2 surface via cadmium pre-electrolyte treatment
Kameni Boumenou, Christian UL; Babbe, Finn; Elizabeth, Amala et al

in Physical Review Materials (2020)

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See detailEffects of Annealing and Light on Co-evaporated Methylammonium Lead Iodide Perovskites using Kelvin Probe Force Microscopy in Ultra-High Vacuum
Gallet, Thibaut UL; Martin Lanzoni, Evandro UL; Redinger, Alex UL

in 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) (2020, February 06)

Careful surface analysis is essential to understand the electronic and ionic behaviors in perovskite absorbers. In this contribution we discuss Kelvin probe force microscopy performed in ultra-high vacuum ... [more ▼]

Careful surface analysis is essential to understand the electronic and ionic behaviors in perovskite absorbers. In this contribution we discuss Kelvin probe force microscopy performed in ultra-high vacuum on as-grown and annealed co-evaporated methylammonium lead iodide perovskite thin films. By comparing the contact potential difference upon annealing and illumination, we find that annealing increases the average workfunction, indicating a change either in doping or in surface composition. Illumination also increases the average workfunction, indicating a p-type absorber, by reducing band bending as the photo-generated carriers screen the surface states. The effect of light shows a two-step process, with a first fast trend, linked to the surface photovoltage and a second slower trend indicating a possible redistribution of mobile charges. [less ▲]

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See detailSurface characterization of epitaxial Cu-rich CuInSe2 absorbers
Lanzoni, Evandro; Spindler, Conrad UL; Ramirez Sanchez, Omar UL et al

in IEEE (2020)

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See detailThe impact of energy alignment and interfacial recombination on the internal and external open-circuit voltage of perovskite solar cells†
Stolterfoht, Martin; Caprioglio, Pietro; Wolff, Christian M. et al

in Energy and Environmental Science (2019)

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See detailVariable chemical decoration of extended defects in Cu-poor Cu2ZnSnSe4 thin films
Schwarz, Torsten; Redinger, Alex UL; Siebentritt, Susanne UL et al

in Physical Review Materials (2019), 3

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See detailFermi-level pinning in methylammonium lead iodide perovskites
Gallet, Thibaut UL; Grabowski, David; Kirchartz, Thomas et al

in Nanoscale (2019)

Hybrid organic inorganic perovskites are ideal candidates for absorber layers in next generation thin film photovoltaics. The polycrystalline nature of these layers imposes substantial complications for ... [more ▼]

Hybrid organic inorganic perovskites are ideal candidates for absorber layers in next generation thin film photovoltaics. The polycrystalline nature of these layers imposes substantial complications for the design of high efficiency devices since the optoelectronic properties can vary on the nanometre scale. Here we show via scanning tunnelling microscopy and spectroscopy that different grains and grain facets exhibit variations in the local density of states. Modeling of the tunneling spectroscopy curves allows us to quantify the density and fluctuations of surface states and estimate the variations in workfunction on the nanometre scale. The simulations corroborate that the high number of surface states leads to Fermi-level pinning of the methylammonium lead iodide surfaces. We do not observe a variation of the local density of states at the grain boundaries compared to the grain interior. These results are in contrast to other reported SPM measurements in literature. Our results show that most of the fluctuations of the electrical properties in these polycrystalline materials arise due to grain to grain variations and not due to distinct electronic properties of the grain boundaries. The measured workfunction changes at the different grains result in local variations of the band alignment with the carrier selective top contact and the varying number of surface states influence the recombination activity in the devices. [less ▲]

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See detailPhysical routes for the synthesis of kesterite
Ratz, T.; Brammertz, G.; Caballero, R. et al

in Journal of Physics : Energy (2019)

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See detailAdvanced characterization and in-situ growth monitoring of Cu(In,Ga)Se2 thin films and solar cells
Abou-Ras, D.; Bär, M.; Caballero, R. et al

in Solar Energy (2018)

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See detailHigh surface recombination velocity limits Quasi-Fermi level splitting in kesterite absorbers
Redinger, Alex UL; Unold, Thomas

in Scientific Reports (2018)

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See detailChemistry and Dynamics of Ge in Kesterite : Toward Band-Gap- Graded Absorbers
Marques, José; Stange, Helena; Hages, Charles J. et al

in Chemistry of Materials (2017), 29

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See detailInvestigation of the SnS/Cu2ZnSnS4 Interfaces in Kesterite Thin-Film Solar Cells
Ren, Yi; Richter, Michael; Keller, Jan et al

in ACS ENERGY LETTERS (2017), 2(5), 976-981

Kesterite Cu2ZnSnS4 (CZTS), having only earth abundant elements, is a promising solar cell material. Nevertheless, the impact of the SnS secondary phase, which often forms alongside CZTS synthesis at high ... [more ▼]

Kesterite Cu2ZnSnS4 (CZTS), having only earth abundant elements, is a promising solar cell material. Nevertheless, the impact of the SnS secondary phase, which often forms alongside CZTS synthesis at high annealing temperature, on CZTS solar cells is poorly studied. We confirm, by means of X-ray diffraction, Raman scattering, and energy dispersive X-ray spectroscopy mapping, that this phase tends to segregate at both the surface and the back side of annealed CZTS films with Cu-poor and Zn-rich composition. Using electron beam-induced current measurements, it is further demonstrated that the formation of SnS on the CZTS surface is harmful for solar cells, whereas the SnS phase can be beneficial for solar cells when it segregates on the CZTS rear. This positive contribution of SnS could stem from a passivation effect at the CZTS/SnS rear interface. This work opens new possibilities for an alternative interface development for kesterite-based photovoltaic technology. [less ▲]

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See detailSilver Doped Cu2SnS3 Absorber Layers for Solar Cells Application
De Wild, Jessica UL; Babbe, Finn UL; Robert, Erika UL et al

in IEEE Journal of Photovoltaics (2017)

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See detailTime resolved photoluminescence on Cu(In, Ga)Se-2 absorbers: Distinguishing degradation and trap states
Redinger, Alex UL; Levcenko, Sergiu; Hages, Charles J. et al

in APPLIED PHYSICS LETTERS (2017), 110(12),

Recent reports have suggested that the long decay times in time resolved photoluminescence (TRPL), often measured in Cu(In, Ga)Se-2 absorbers may be a result of detrapping from sub-bandgap defects. In ... [more ▼]

Recent reports have suggested that the long decay times in time resolved photoluminescence (TRPL), often measured in Cu(In, Ga)Se-2 absorbers may be a result of detrapping from sub-bandgap defects. In this work, we show via temperature dependent measurements, that long lifetimes >50 ns can be observed that reflect the true minority carrier lifetime not related to deep trapping. Temperature dependent time resolved photoluminescence and steady state photoluminescence imaging measurements are used to analyze the effect of annealing in air and in a nitrogen atmosphere between 300K and 350K. We show that heating the Cu(In, Ga)Se-2 absorber in air can irreversibly decrease the TRPL decay time, likely due to a deterioration of the absorber surface. Annealing in an oxygen-free environment yields a temperature dependence of the TRPL decay times in accordance with Schockley Read Hall recombination kinetics and weakly varying capture cross sections according to T-0.6. Published by AIP Publishing. [less ▲]

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See detailIdentifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials
Hages, Charles J.; Redinger, Alex UL; Levcenko, Sergiu et al

in Advanced Energy Materials (2017)

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See detailOptical properties of Cu2ZnSnSe4 thin films and identification of secondary phases by spectroscopic ellipsometry
Demircioglu, Ozden; Salas, Jose Fabio Lopez; Rey, Germain UL et al

in OPTICS EXPRESS (2017), 25(5), 5327-5340

We apply spectroscopic ellipsometry (SE) to identify secondary phases in Cu2ZnSnSe4 (CZTSe) absorbers and to investigate the optical properties of CZTSe. A detailed optical model is used to extract the ... [more ▼]

We apply spectroscopic ellipsometry (SE) to identify secondary phases in Cu2ZnSnSe4 (CZTSe) absorbers and to investigate the optical properties of CZTSe. A detailed optical model is used to extract the optical parameters, such as refractive index and extinction coefficient in order to extrapolate the band gap values of CZTSe samples, and to obtain information about the presence of secondary phases at the front and back sides of the samples. We show that SE can be used as a non-destructive method for detection of the secondary phases ZnSe and MoSe2 and to extrapolate the band gap values of CZTSe phase. (C) 2017 Optical Society of America [less ▲]

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See detailFormation of nanometer-sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin-films and their effect on solar cell efficiency
Schwarz, Torsten; Cojocaru-Miredin, Oana; Mousel, Marina et al

in ACTA MATERIALIA (2017), 132

Atom probe tomography and transmission electron microscopy are used to study the formation of nano sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin -films. For a Cu -rich precursor, which was deposited at 320 ... [more ▼]

Atom probe tomography and transmission electron microscopy are used to study the formation of nano sized Cu-Sn-Se particles in Cu2ZnSnSe4 thin -films. For a Cu -rich precursor, which was deposited at 320 degrees C under Cu- and Zn-rich growth conditions, Cu2-xSe grains at the surface are detected. During annealing the precursor at 500 degrees C in a SnSe + Se atmosphere most of the Cu2-xSe is transformed to Cu2ZnSnSe4 via the consumption of excessive ZnSe and incorporation of Sn. However, atom probe tomography studies also reveal the formation of various nanometer-sized Cu-Sn-Se particles close to the CdS/Cu(2)ZnSnSe4 interface. One of those particles has a composition close to the Cu2SnSe3 compound. This phase has a smaller band gap than Cu2ZnSnSe4 and is proposed to lead to a significant drop in the open -circuit voltage and could be the main cause for a detrimental p-n junction and the zero efficiency of the final device. Possible effects of the other phases on solar cell performance and formation mechanisms are discussed as well. (C)2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. [less ▲]

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See detailImpact of annealing on electrical properties of Cu2ZnSnSe4 absorber layers
Weiss, Thomas UL; Redinger, Alex UL; Rey, Germain UL et al

in Journal of Applied Physics (2016), 120

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See detailOvercoming the Voc limitation of CZTSe solar cells
Risch, L.; Vauche, L.; Redinger, Alex UL et al

in IEEE (2016)

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See detailDeep Defects in Cu2ZnSnðS;SeÞ4 Solar Cells with Varying Se Content
Levcenko, S.; Just, J.; Redinger, Alex UL et al

in Physical Review Applied (2016)

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See detailIntragrain charge transport in kesterite thin films-Limits arising from carrier localization
Hempel, Hannes; Redinger, Alex UL; Repins, Ingrid et al

in JOURNAL OF APPLIED PHYSICS (2016), 120(17),

Intragrain charge carrier mobilities measured by time-resolved terahertz spectroscopy in state of the art Cu2ZnSn(S,Se)(4) kesterite thin films are found to increase from 32 to 140 cm(2) V-1 s(-1) with ... [more ▼]

Intragrain charge carrier mobilities measured by time-resolved terahertz spectroscopy in state of the art Cu2ZnSn(S,Se)(4) kesterite thin films are found to increase from 32 to 140 cm(2) V-1 s(-1) with increasing Se content. The mobilities are limited by carrier localization on the nanometer-scale, which takes place within the first 2 ps after carrier excitation. The localization strength obtained from the Drude-Smith model is found to be independent of the excited photocarrier density. This is in accordance with bandgap fluctuations as a cause of the localized transport. Charge carrier localization is a general issue in the probed kesterite thin films, which were deposited by co-evaporation colloidal inks, and sputtering followed by annealing with varying Se/S contents and yield 4.9\%-10.0 efficiency in the completed device. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). [less ▲]

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