References of "Redinger, Alex 50026033"
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See detailInhomogeneities in lead halide perovskite absorbers revealed by quantitative Photoluminescence Imaging
Phirke, Himanshu UL; Singh, Ajay UL; Hieulle, Jeremy UL et al

in Phirke, Himanshu; Singh, Ajay; Hieulle, Jeremy (Eds.) et al Inhomogeneities in lead halide perovskite absorbers revealed by quantitative Photoluminescence Imaging (2022, April 20)

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See detailImpact of metallic potassium post-deposition treatment on epitaxial Cu(In, Ga)Se2
Martin Lanzoni, Evandro UL; Ramirez Sanchez, Omar UL; Phirke, Himanshu UL et al

in Thin Solid Films (2021)

Alkali post-deposition treatments (PDTs) of Cu(In, Ga)Se2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via ... [more ▼]

Alkali post-deposition treatments (PDTs) of Cu(In, Ga)Se2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via evaporation of alkali fluorides in a selenium atmosphere onto a hot substrate. In this work, an alkali metal dispenser was used to evaporate pure metallic potassium onto epitaxial CIGSe absorbers. Subsequently, the absorber layers were heated in-situ to monitor chemical reactions and diffusion into the bulk. Due to the absence of grain boundaries, fluorine, and selenium, the effect of K on CIGSe absorber properties can be directly monitored. We find that potassium effectively diffuses into the bulk of epitaxial CIGSe absorber layers. The diffusion depends on the Cucontent of the CIGSe absorbers, in which Cu-depleted films present higher diffusion rates of K. Photoluminescence (PL) imaging corroborates that K in the bulk of the CIGSe absorber increases the PL yield, suggesting a passivation of defects or an increase in doping. This work highlights that alkali PDTs are not limited by interface and grain boundary modifications but also changes the absorber bulk properties, which needs to be taken into account. [less ▲]

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See detailRoadmap on organic–inorganic hybrid perovskite semiconductors and devices
Schmidt-Mende, Lukas; Dyakonov, Vladimir; Olthof, Selina et al

in APL Materials (2021)

Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite ... [more ▼]

Metal halide perovskites are the first solution processed semiconductors that can compete in their functionality with conventional semiconductors, such as silicon. Over the past several years, perovskite semiconductors have reported breakthroughs in various optoelectronic devices, such as solar cells, photodetectors, light emitting and memory devices, and so on. Until now, perovskite semiconductors face challenges regarding their stability, reproducibility, and toxicity. In this Roadmap, we combine the expertise of chemistry, physics, and device engineering from leading experts in the perovskite research community to focus on the fundamental material properties, the fabrication methods, characterization and photophysical properties, perovskite devices, and current challenges in this field. We develop a comprehensive overview of the current state-of-the-art and offer readers an informed perspective of where this field is heading and what challenges we have to overcome to get to successful commercialization. [less ▲]

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See detailThe impact of Kelvin probe force microscopy operation modes and environment on grain boundary band bending in perovskite and Cu(In,Ga)Se2 solar cells
Martin Lanzoni, Evandro UL; Gallet, Thibaut UL; Spindler, Conrad UL et al

in Nano Energy (2021), 88

An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very ... [more ▼]

An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very high and hence limit the solar cell device performance. Kelvin Probe Force Microscopy (KPFM) is the method of choice to investigate GB band bending on the nanometer scale and thereby helps to develop passivation strategies. Here, it is shown that the workfunction, measured with amplitude modulation (AM)-KPFM, which is by far the most common KPFM measurement mode, is prone to exhibit measurement artifacts at grain boundaries on typical solar cell absorbers such as Cu(In,Ga)Se2 and CH3NH3PbI3. This is a direct consequence of a change in the cantilever–sample distance that varies on rough samples. Furthermore, we critically discuss the impact of different environments (air versus vacuum) and show that air exposure alters the GB and facet contrast, which leads to erroneous interpretations of the GB physics. Frequency modulation (FM)-KPFM measurements on non-air-exposed CIGSe and perovskite absorbers show that the amount of band bending measured at the GB is negligible and that the electronic landscape of the semiconductor surface is dominated by facet-related contrast due to the polycrystalline nature of the absorbers. [less ▲]

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See detailCo-evaporation of CH3NH3PbI3: How Growth Conditions Impact Phase Purity, Photostriction, and Intrinsic Stability
Gallet, Thibaut UL; Goncalinho Poeira, Ricardo Jorge UL; Martin Lanzoni, Evandro UL et al

in ACS Applied Materials and Interfaces (2021), 13(2), 26422653

Hybrid organic–inorganic perovskites are highly promising candidates for the upcoming generation of single- and multijunction solar cells. Despite their extraordinarily good semiconducting properties ... [more ▼]

Hybrid organic–inorganic perovskites are highly promising candidates for the upcoming generation of single- and multijunction solar cells. Despite their extraordinarily good semiconducting properties, there is a need to increase the intrinsic material stability against heat, moisture, and light exposure. Understanding how variations in synthesis affect the bulk and surface stability is therefore of paramount importance to achieve a rapid commercialization on large scales. In this work, we show for the case of methylammonium lead iodide that a thorough control of the methylammonium iodide (MAI) partial pressure during co-evaporation is essential to limit photostriction and reach phase purity, which dictate the absorber stability. Kelvin probe force microscopy measurements in ultrahigh vacuum corroborate that off-stoichiometric absorbers prepared with an excess of MAI partial pressure exhibit traces of low-dimensional (two-dimensional, 2D) perovskites and stacking faults that have adverse effects on the intrinsic material stability. Under optimized growth conditions, time-resolved photoluminescence and work functions mapping corroborate that the perovskite films are less prone to heat and light degradation. [less ▲]

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See detailNanoscale interfacial engineering enables highly stable and efficient perovskite photovoltaics
Krishna, Anurag; Zhang, Hong; Zhou, Zhiwen et al

in Energy and Environmental Science (2021)

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See detailElectronic and compositional properties of the rear-side of stoichiometric CuInSe2 absorbers
Kameni Boumenou, Christian UL; Elisabeth, Amala; Babbe, Finn et al

in Progress in Photovoltaics (2020)

In-depth understanding and subsequent optimization of the contact layers in thin film solar cells are of high importance in order to reduce the amount of nonradiative recombination and thereby improve ... [more ▼]

In-depth understanding and subsequent optimization of the contact layers in thin film solar cells are of high importance in order to reduce the amount of nonradiative recombination and thereby improve device performance. In this work, the buried MoSe2/CuInSe2 interface of stoichiometric absorbers is investigated with scanning tunneling spectroscopy and Kelvin probe force microscopy combined with compositional measurements acquired via photo-electron spectroscopy after a mechanical lift-off process. We find that the local density of states, as measured with scanning tunneling spectroscopy, is similar to the front-side of ultra-high vacuum annealed CISe absorbers. The grain boundaries exhibit a weak upward band bending, opposite to Cu-poor CuGaSe2, and we measure an increased Cu accumulation at the rear CISe surface compared to the bulk composition and a non-zero concentration of Cu on the Mo-side. Grazing incidence X-ray diffraction measurements corroborate that a small amount of a CuxSe secondary phase is present at the MoSe2/CuInSe2 interface in contrast to reports on Cu-poor material. Our findings shed new light into the complex interface formation of CuInSe2-based thin film solar cells grown under Cu-rich conditions. [less ▲]

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

in IEEE Photovoltaic Specialists Conference. Conference Record (2019, July)

We investigated the electrical properties of epitaxial Cu-rich CuInSe 2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient ... [more ▼]

We investigated the electrical properties of epitaxial Cu-rich CuInSe 2 by Kelvin probe force microscopy (KPFM) under ambient and ultra-high vacuum conditions. We first measured the sample under ambient conditions before and after potassium cyanide (KCN) etching. In both cases, we do not see any substantial contrast in the surface potential data; furthermore, after the KCN etching we observed outgrowths with a height around 2nm over the sample surface. On the other hand, the KPFM measurements under ultra-high vacuum conditions show a work function dependence according to the surface orientation of the Cu-rich CuInSe 2 crystal. Our results show the possibility to increase the efficiency of epitaxial Cu-rich CuInSe 2 by growing the materials in the appropriated surface orientation where the variations in work function are reduced. [less ▲]

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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 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 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 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 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 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 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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