Arnaud Etcheberry - Academia.edu (original) (raw)

Papers by Arnaud Etcheberry

Thin Solid Films, 2019

A proper control of Ga concentration profile is mandatory to achieve high efficiency Cu(In,Ga)Se ... more A proper control of Ga concentration profile is mandatory to achieve high efficiency Cu(In,Ga)Se 2 (CIGS) solar cells. At low temperature, deep gradients, detrimental for carriers' diffusion, are obtained when CIGS is deposited with a standard three-stage process: an optimization of the process is needed. In this study, we show the impact of a modify three-stage process on the depth of the notch by introducing Ga flux during the second stage from 0 nm/min to 1.1 nm/min. A higher open circuit voltage compensated by a lower short current density is obtained due to higher band gap energy. The surface and the bulk of the CIGS layer was analyzed at the end of the second stage by coupling different characterization techniques: glow discharge optical emission spectroscopy, Raman and X-ray photoelectrons spectroscopy. The presence of binary compounds as well as a Ga enrichment at the end of the second stage are observed when Ga is introduced during the second stage.

IEEE Journal of Photovoltaics, Sep 1, 2018

Flexible, lightweight, Cu(In,Ga)Se2 photovoltaic technology is becoming more and more popular, th... more Flexible, lightweight, Cu(In,Ga)Se2 photovoltaic technology is becoming more and more popular, thanks to the very high efficiencies already achieved (>20%) and to the possible employment of roll-to-roll deposition techniques, offering new application opportunities. In this paper, we aim to improve the understanding and performances of recently discovered new front surface engineering approaches. We show that the improvement of Voc generally observed using heavy alkali (below Na) can be boosted by adding indium during the alkali postdeposition treatments (PDTs). The obtained modification of the absorber using NaF/KF + In PDT leads to an improvement of Voc by 20 mV with respect to NaF/KF PDT and by almost 50 mV with respect to NaF-PDT only. The electrical performances of solar cells prepared with different PDTs are analyzed and discussed in light of structural and optical characterization data, supported by physical modeling. We show that KF PDTs modify the absorber over a thin region close to the surface, and also deep in the bulk of the film. Our results with KF show a record efficiency of 18.1% without antireflecting coating (ARC), a value that is close to the highest reported value of 20.4% (with ARC).

World Conference on Photovoltaic Energy Conversion, Oct 26, 2012

ABSTRACT Conventional light trapping techniques are inefficient at the sub-wavelength scale. This... more ABSTRACT Conventional light trapping techniques are inefficient at the sub-wavelength scale. This is the main limitation for the thickness reduction of thin-film solar cells below 500nm. We propose a novel architecture for broadband light absorption in ultra-thin active layers based on plasmonic nano-cavities and multi-resonant mechanism. Strong light enhancement will be shown numerically for photovoltaic materials such as CIGSe and GaAs. First experiments on ultrathin nano-patterned CIGSe solar cells will be presented.

MRS Proceedings, 2003

This paper presents optimization studies on the formation of cadmium free buffer layers for high ... more This paper presents optimization studies on the formation of cadmium free buffer layers for high efficiency copper indium diselenide (CIGS) thin film solar cells using a vapor phase route. Indium sulfide layers have been deposited on CIGS substrates by Atomic Layer Deposition (ALD) at substrate temperatures between 140 and 260 °C using indium acetylacetonate and hydrogen sulfide precursors. The parametric study of the deposition temperature shows an optimal value at about 220°C, leading to an efficiency of 16.4 % which is a technological breakthrough. The analysis of the device shows that indium sulfide layers give an improvement of the blue response of the cells as compared a standard CdS processed cell, due to a high apparent band gap (2.7-2.8 eV), higher open circuit voltages (up to 665 mV) and fill factor (78 %). This denotes high interface quality of the system. Atomic diffusion processes of sodium and copper in the buffer layer are evidenced.

Advanced Functional Materials

Understanding the effects of X‐rays on halide perovskite thin films is critical for accurate and ... more Understanding the effects of X‐rays on halide perovskite thin films is critical for accurate and reliable characterization of this class of materials, as well as their use in detection systems. In this study, advanced optical imaging techniques are employed, both spectrally and temporally resolved, coupled with chemical characterizations to obtain a comprehensive picture of the degradation mechanism occurring in the material during photoemission spectroscopy measurements. Two main degradation pathways are identified through the use of local correlative physico‐chemical analysis. The first one, at low X‐Ray fluence, shows minor changes of the surface chemistry and composition associated with the formation of electronic defects. Moreover, a second degradation route occurring at higher fluence leads to the evaporation of the organic cations and the formation of an iodine‐poor perovskite. Based on the local variation of the optoelectronic properties, a kinetic model describing the diffe...

Journal of Applied Physics, 2021

Electronic passivation of III-V surfaces is essential for applications in optoelectronic devices.... more Electronic passivation of III-V surfaces is essential for applications in optoelectronic devices. A key aspect is the measurement of the surface recombination properties which can be done by various techniques including transient photoluminescence (TRPL) or luminescence quantum yield. These measurement techniques are always indirect since they suppose postulating a mathematical model for the data interpretation. Most common models use the notion of surface recombination velocity to quantify the surface recombination. In this paper we demonstrate on InP substrate than this notion is not always sufficient to represent the injection dependence of the surface phenomena. The study of power dependence of TRPL decays coupled with Modulated Photoluminescence (MPL) spectra on four samples from the same wafer with different surface treatments (epi-ready, freshly cleaned, after air exposure and with poly-phosphazen passivation) allows us for discriminating between bulk and surface properties. We introduce surface defect trapping as an alternative to explain TRPL decays and MPL phase excitation power dependences of the three non-passivated samples. Surface trap parameters such as capture cross section and defect density are extracted. The passivated sample exhibits invariant response shape on eight orders of magnitude of illumination. The stability of the PL response at high flux is in agreement with the perfect stability of the passivation layer which is able to protect the InP surface without chemical changes over more than one year. They are linked to the nature of the Passivation layer/InP interface. Other surface treatments were found to have an injection dependent response The following article has been accepted by the Journal of Applied Physics.

Time resolved Photoluminescence is a standard technique to probe the recombination paths in photo... more Time resolved Photoluminescence is a standard technique to probe the recombination paths in photovoltaic semiconductors. However, the effect of slow mechanisms as de-trapping often appears at the end of the decays, and are sometimes covered by the noise. Furthermore, in complex decay cases, one has to postulate recombination mechanisms and to perform to simulations, without insurance that the fitting procedure will lead to unique fits. In this context we upgraded our Frequency Domain setup, also known as High Frequency Modulated Photoluminescence up to 100 MHz. We coupled the both kind of measurements, TRPL and HFMPL with drift diffusion simulation including light reabsorption. Finally, we present several kind of III-V material responses and show how the response can be interpreted more reliably using the 2 methods and the simulations.

2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC), 2018

CIGS based solar cells are still part of the most popular solar cells developed. A chemical study... more CIGS based solar cells are still part of the most popular solar cells developed. A chemical study is presented here by using XPS measurements, characterizing the surface chemistry and reactivity, with a focus on deoxidation and further ageing products, among which binary compounds and oxides can be found. Different chemical treatments are also suggested to adjust the surface composition of CIGS materials and to determine the re-oxidation delay. A specific point will be also discussed about the comparative evolution of alkali element distribution during the ageing of conventional CIGS/glass and CIGS/flexible substrate systems, requiring in this case an external alkali source.

Applied Surface Science, 2021

We performed a comprehensive study of Cu(In,Ga)Se2 (CIGS) surface reactivity in air, focusing on ... more We performed a comprehensive study of Cu(In,Ga)Se2 (CIGS) surface reactivity in air, focusing on the evolution of the surface chemistry via X-ray photoemission spectroscopy (XPS). By using the different transitions (photopeaks and X-ray Auger electron spectroscopy transitions) available on XPS spectra, in order to probe different surface thicknesses, complementary chemical information is provided to investigate the surface reactivity mechanism of CIGS surface and especially highlight the importance of the relative humidity rate of the atmosphere. Indeed, by maintaining a relative humidity of 20%, we demonstrate that

Electrochemistry Communications, 2020

Indium phosphide (InP) surfaces are greatly affected by ionic bombardment. We investigate the res... more Indium phosphide (InP) surfaces are greatly affected by ionic bombardment. We investigate the resulting surface perturbation through the use of the complementary analytical techniques of electrochemistry and X-ray photoelectron spectroscopy (XPS). Following bombardment, modifications to the surface were identified by a reduction in the dark open circuit potential in comparison to the pristine state. Through XPS studies, it was found that the sputtered surface was enriched with a metallic-like In contribution, which oxidized upon exposure to air. Cyclic voltammetry measurements confirmed this observation, with initial cathodic features related to an oxidized metallic In-enriched layer on the InP surface. Repeated cyclic voltammetry experiments resulted in the formation of a more In-rich overlayer due to a specific oxidation/reduction phenomenon. This behavior is very similar to that obtained by cathodic decomposition on InP surfaces.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2019

Photovoltaic cells based on CIGS [Cu(In,Ga)Se2] absorber technology are among the most efficient ... more Photovoltaic cells based on CIGS [Cu(In,Ga)Se2] absorber technology are among the most efficient thin film solar cells and already an industrial reality. Room for improvement is still possible in the manufacturing process to approach the theoretical ultimate efficiency. This not only requires an optimal absorber material but also the control of the CIGS interface chemistry, especially at the front side with the buffer layer which represents one of the main challenges. In this paper, thanks to x-ray photoelectron spectroscopy (XPS) analysis, the CIGS surface chemical composition is studied after acid (HCl) and basic (KCN) samples dipping. Both are regularly employed to prepare CIGS surfaces. XPS monitoring of the surface composition evolution under air aging at an ambient atmosphere and over a period of 120 days is presented, bringing fundamental information about the surface oxidation trends. If the HCl treatment gives a remarkable deoxidation state for the CIGS surface, it also yie...

ECS Transactions, 2019

III-V materials have yet proved to be promising candidates for photovoltaic applications. Solar c... more III-V materials have yet proved to be promising candidates for photovoltaic applications. Solar cell technologies based on III-V semiconductors are competitive in term of fabrication cost but also have the potential to reach the highest photovoltaic efficiencies. To overcome the 30% conversion limitation established for a single junction, the Shockley Queisser limit [1], due to different losses that cannot be avoided (transmission, thermalization, emission…), different solar cell architectures have been proposed. One of them, multi-junctions, are using a stack of absorbing materials enabling to cover a wider part of the solar spectrum with high efficiency due to their optimized bang-gaps. Among other recent concepts, intermediate band solar cells have gained interest with predicted efficiency greater than 60% (under maximum concentration) and almost 48.2% under one sun [2], similar to the efficiency potential of a 3 material stack, but with a single material. By implementing quantum dots at the surface of a III-V single layer, an intermediate band can be generated [3, 4] and tuned by changing the quantum dots nature, size and shape. More complex structures with multi-stacked quantum dots have also been studied [5]. The present work focuses on the preparation of III-V quantum dots surfaces using wet chemistry. Not only dots evolution but also the development of a specific soaking to eliminate the wetting layer, detrimental for optoelectronic properties, will be shown. Numerous studies and formulation have been reported for chemical etching of III-V semiconductors [6]. Nevertheless, the remaining challenge concerns the implementation of this chemical engineering at nanometric scale [7], in consistency with the miniaturization trend and requirements of the materials, structures and devices. The study is carried out on InAs and InGaAs quantum dots grown by MBE on GaAs substrates. They present different surface densities. The structure of the samples is presented figure 1 where the wetting layer, essential for the quantum dots epitaxial growth, is illustrated. A multi-technique methodology combining XPS, AFM and nano-Auger is employed to precisely determine the surface chemical and morphologic modifications from micrometric to nanometric scale. Thanks to XPS, the evolutions of the fine chemistries of quantum dots and their surface are accessible, giving crucial information about the dissolution processes and enabling to re-adjust the experimental conditions. In Figure 1 b, the In3d photopeak evolution with the chemical treatment employed on a sample presenting only the wetting layer is shown. Indium atoms are only present in the wetting layer in this case. Thus it represents the tracking element indicative of the maintenance, thinning or elimination of this layer. The complementary use of AFM brings the evidence of the dots conservation or disappearance as illustrated Figure 1c. Nano-Auger provides additional information on local chemistry. Various formulations, in acidic or base media, are developed to enable a differential dissolution between the wetting layer and the quantum dots. Both oxidation-deoxidation cycling and direct dipping procedures were experimented and optimized taking account the differences in oxides solubility. The various scenarios likely to occur during deoxidation are presented Figure 1a, the elimination of QD being also possible by the dissolution of the wetting layer below. Finally, a comparison of capabilities for nano-etching and possible selectivity of the different solutions considered here will be presented. References [1] W. Shockley and H.J. Queisser, J. Appl. Phys. 32 (1961), 510. [2]A. Luque, A. Marti, Phys. Rev .Lett. 78 (1997) 5014-5017. [3] T. Sogabe, Y. Shoji, M. Ohba, K. Yoshida, R.Tamaki, H.-F. Hong, C.-H. Wu, C.-T. Kuo, S. Tomić, and Y. Okada, Scientific Reports (Nature Publishing Group), 4, (2014)/4/25. doi:10.1038/srep04792. [4] E. Lopez, A. Datas, I. Ramiro, P.G. Linares, E. Antolin, I. Artacho, A. Marti, A. Luque, Y. Shoji, T. Sogabe, A. Ogura, Y. Okada, Sol. Energy Mater Sol. Cells 149 (2016) 15-18. [5] T. Kada, S. Asahi, T. Kaizu, Y. Harada and T. Kita, Phys. Rev. B 91 (2015) 201303(R). [6] A.R. Clawson, Reports: a review journal, Mater. Sci. Eng. 31 (2001) 1-438. [7] D. H. van Dorp, S. Arnauts, M. Laitinen, T. Sajavaara, J. Meersschaut, T. Conard and John J. Kelly, Appl. Surf. Sci. 465, (2018), Pages 596-606. Figure 1

Electrochemistry Communications, 2018

This study explores the rich chemistry of elemental selenium reduction to monoselenide anions. Th... more This study explores the rich chemistry of elemental selenium reduction to monoselenide anions. The simplest possible homogeneous electron transfer occurs with free electrons, which is only possible in plasmas; however, alkali metals in liquid ammonia can supply unbound electrons at much lower temperatures, allowing in situ analysis. Here, solvated electrons reduce elemental selenium to K 2 Se, a compound relevant for alkali metal doping of Cu(In,Ga)Se 2 solar cell material. It is proposed that the reaction follows pseudo first-order kinetics with an inner-sphere or outer-sphere oxidation semi reaction mechanism depending on the concentration of solvated electrons.

LGEP 2011 ID = 758International audienc

In thin film polycrystalline CdS/CIGS heterojunction solar cells, understanding the intrinsic and... more In thin film polycrystalline CdS/CIGS heterojunction solar cells, understanding the intrinsic and interface defect properties is crucial to optimize their performances. In this paper, we focus our attention on the CdS/CIGS hetero-interface at different stages of its formation. All investigations were carried out on CIGS co-evaporated samples elaborated in pilot-line conditions onto which the CdS layer was deposited by chemical bath deposition (CBD). This latter chemical process involves the use of a NH, solution that modifies the ClGS surface composition. In order to separate the respective role of the NH/sub 3/ bath and the CdS layer thickness , we have investigated samples elaborated with several NH/sub 3/ pretreatment time of CIGS surface prior to CdS deposition. Admittance spectroscopy was used to follow the evolution of the hetero-interface defects properties.

We have studied Cu(In,Ga)Se 2 chemical and electric behavior and composition engineering. All inv... more We have studied Cu(In,Ga)Se 2 chemical and electric behavior and composition engineering. All investigations were carried out on co-evaporated Cu(In,Ga)Se 2 (CIGS) samples onto which different surface etching were applied. XPS was used to determine the composition evolution of the CIGS surface with treatment and CIGS/CdS interface. Electric measurements were studies using admittance spectroscopy and Kelvin probe. Work presented will give a progress report on three years of collaboration relating to the study of the mechanisms of formation of CIGS/CdS interfaces.

Current versus voltage and temperature (IVT) characterizations have been performed on CIGS (Cu(In... more Current versus voltage and temperature (IVT) characterizations have been performed on CIGS (Cu(In,Ga)Se2 solar cells previously submitted to a chemical etching of their absorber layer. This study aims to investigate the changes in recombination paths, if any, when the absorber layer thickness is reduced. Diode parameters saturation current, ideality factor, series and parallel resistances were extracted from the IVT curves through a method based on the one-diode model. No clear evolution with thickness of the parameters was found among the etched samples. Temperature-dependent ideality factor and very high values of the saturation current activation energy were deduced from the data, denoting a tunneling-enhanced interface recombination process. A different behavior was however detected between the non etched control sample and the others that could be due to a modification of the surface of the CIGS layer during the very early stages of the etch.

The influence of CIGSe surface roughness over the photovoltaic parameters is reported. The as dep... more The influence of CIGSe surface roughness over the photovoltaic parameters is reported. The as deposited rough CIGSe surface is smoothed using a chemical etch, and the bare CIGSe surface is characterized by SEM, AFM and Reflectivity. As the roughness decreases, the total reflectivity of the CIGSe surface increases, but the ratio of diffuse reflectivity decreases as expected for a more flat surface. The sample are processed into solar cells and characterized by I(V) measurements. While the open circuit voltage and the fill factor remains constant, the short circuit current decreases with the decreased roughness, resulting in a reduction of the solar cell efficiency from 14% down to 11%. Quantum efficiency and reflectivity measurements are performed on the solar cells to study the mechanisms involved.

Research on CIGS-based photovoltaic cells is developing towards the use of wide band-gap and non-... more Research on CIGS-based photovoltaic cells is developing towards the use of wide band-gap and non-toxic materials to replace the cadmium sulphide buffer layers that is used as an interfacial buffer layer. Efficiency level of 15-16 % has been reached using CBD-Zn(S,O,OH)/rf-(Zn,Mg)O buffer layers. However contrary to cells with CdS buffer layer, CBD-Zn(S,O,OH)/rf-ZnMgO cells require post-air-annealing and light-soaking procedures to achieve optimal conversion efficiencies. This paper addresses the optoelectronic parameters affected by these post-treatment effects. First the impact of heat treatment and light soaking has been studied by comparing the properties of different combinations of CBD-CdS, CBD-Zn(S,O,OH), rf-i-ZnO, rf-ZnMgO, layers. The gradual impact of light soaking on CIGS/CBD-Zn(S,O,OH)/rf-ZnMgO/ZnO:Al solar cell characteristics has been analyzed prior to and after annealing, revealing a dominant improvement in the fill factor. Temperature dependant current-voltage measure...