In this article are investigated the optical and structural properties of copper oxide thin films deposited by ultrasonic spray pyrolysis and the effect of the substrate temperature and the D-sorbitol precursor solution reducing agent. The Cu2O/CuO phase transition, a key factor for the development of this metal oxide for photovoltaics and other applications, is studied using X-ray diffraction, confocal micro-Raman and transmittance spectroscopy. The obtained structural and optical properties are correlated to analyze the phase transition and the effect of the reducing agent concentration combined to the controlled and precisely defined preparation temperature. The study permitted to use a relatively low preparation temperature of 230 °C to produce a single Cu2O phase using the D-sorbitol reducing agent. The optimized structural and optical properties were obtained without the need of using D-sorbitol in excess compared to copper acetate, as usually done when using glucose, thereby reducing the density of defects and improving electrical properties for optoelectronic applications.

The Indium Gallium Nitride (InGaN) alloy has the required potentialities to be a material of choice used in the next generation high efficiency solar cells. Indeed, the mere change in its Indium composition allows its absorption to cover the whole solar spectrum. The other main advantages of InGaN, in addition to its tunable bandgap, are a high absorption coefficient, a high stability and radiation tolerance. However, challenging issues remain to address: (i) the difficulty to elaborate sufficiently thick monocrystalline InGaN layers with a high Indium content; (ii) the high defects density and the spontaneous and piezoelectric polarizations; (iii) the p-doping which remains difficult to master. A review of this promising technology for solar cells is provided and present challenges and future perspectives are presented, including the use of InGaN multijunction structures and a new InGaN Schottky Based Solar Cells (SBSC) structure.

Purpose – The purpose of this paper is to investigate the effect of growth temperature on the evolution of indium incorporation and growth process of InGaN/GaN heterostructures. Design/methodology/approach – To examine this effect, the InGaN/GaN heterostructures were grown using Taiyo Nippon Sanso Corporation (TNSC) metal organic chemical vapor deposition (MOCVD) SR4000-HT system. The InGaN/GaN heterostructures were epitaxially grown on 3.4 μm undoped-GaN (ud-GaN) and GaN nucleation layer respectively over a commercial 2” c-plane flat sapphire substrate (FSS). The InGaN layers were grown at different temperature setting ranging from 860°C to 820°C in a step of 20°C. The details structural, surface morphology and optical properties were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM) and ultraviolet-visible (UV-Vis) spectrophotometer, respectively. Findings – InGaN/GaN heterostructure with indium composition up to 10.9% has been successfully grown using MOCVD technique without any phase separation detected within the sensitivity of the instrument. Indium compositions were estimated through simulation fitting of XRD curve and calculation of Vegard’s law from UV-Vis measurement. The thickness of the structures was determined using Swanepoel method and the FE-SEM cross-section image. Originality/value – This paper report on the effect of MOCVD growth temperature on the growth process of InGaN/GaN heterostructure which are of interest in solid state lighting technology especially in light emitting diodes (LEDs) and solar cells application.

All-oxide photovoltaics is a new and very promising technology for low cost and efficient solar cells using earth-abundant and environmentally compatible materials. To match the requirements of this technology, beyond the optimization of the absorber layer, it is crucial to elaborate window and transport layers with excellent optical and structural properties in a wide range of thickness. Among the oxide materials, zinc oxide is a key material for the realization of these layers in the targeted all-oxide solar cells. Beside the low toxicity and abundance of ZnO, the reduction of the environmental footprint of photovoltaic technology could benefit from the low energy and low precursor consumption of the ultrasonic spray pyrolysis (USP) process. In addition to the environmental aspects, the USP process combines many advantages compared to conventional methods such as low-cost and large-scale production capability. The potential for elaboration of thin films of suitable structural and optical properties of this process combined with the previously mentioned advantages makes it of high interest for the future of photovoltaics. To date, the optical and structural properties of ZnO elaborated by USP have not been fully investigated with respect to the precursor solution concentration, which could have a strong impact on these properties and thus on the performances of the solar cell. ZnO thin films were deposited using the USP process after a precise optimization of the main growth conditions, namely the substrate temperature, spray pressure, nozzle speed and precursor solution flux, according to a specific design of experiment. ZnO films were confirmed to be conductive by showing resistivity values in the order of 1 Ω.cm. For this study, we used X-ray diffraction (XRD) and Raman spectroscopy to analyze the crystal structure, orientation and texture coefficient. Our results show that the preferential orientation can be controlled to be either (002) or (100) by adjusting the precursor solution concentration. On the one hand, the precise control of the orientation allows to better control the optical properties, that are crucial in our application, and, on the other hand, limit the defects at the heterointerface. The morphological properties were studied using atomic force microscopy and were correlated to the structural properties of the ZnO thin films. For instance, high consistency was evidenced between the AFM measured grain size and the XRD measured crystallite size. Finally, the optical properties were studied from UV/visible transmittance spectroscopy. The deposited ZnO films exhibit high transmittance above 90 % for the whole concentration range of the precursor solution with a maximum as high as 95 %. The resulting optical and structural properties could benefit to the performances of all-oxide solar cells deposited by USP.

ZnMgO thin films are elaborated by ultrasonic spray pyrolysis using water-based solutions only, for an Mg composition as high as 70 mol%. The elaboration conditions are optimized and the structural, optical, and electrical properties of the ZnMgO films are investigated with respect to the Mg concentration using X-Ray fluorescence, X-Ray diffraction, atomic force microscopy, Raman and transmission spectroscopies, and van der Pauw/Hall effect electrical measurements. The obtained properties are correlated to analyze the miscibility and, for single-phase material, the optoelectronic, optical, and transport properties with respect to the composition. The elaborated thin films exhibit a monotonous increase in the bandgap, a high transparency above 90% in the visible region, and a dramatic decrease in the n-type carrier concentration, for Mg compositions lower than 30 mol% where wurtzite single-phase structure is evidenced. A compensation mechanism of the n-type dopants in ZnO, attributed to interstitial Zn which acts as a shallow donor, is given as an explanation of this variation of the carrier concentration. These optoelectronic properties show that ZnMgO can be efficiently used in applications such as UV detectors and solar cells.

Le présent document se propose de retracer succinctement les actions entreprises par l'Université de Lorraine dans le cadre de sa politique Science Ouverte, elle-même dans les pas du premier Plan National pour la Science Ouverte de 2018 (PNSO1), puis d'esquisser les grands enjeux en la matière pour l'établissement, s'inspirant pour ce faire du deuxième Plan National pour le Science Ouverte, publié en 2021 (PNSO2), des initiatives de la Comission Européenne et de la récente recommandation de l'Unesco. La première partie présentera donc le bilan des réalisations, en le structurant via les grands axes du PNSO1 ; tout comme la deuxième partie, qui s'efforcera d'anticiper les grands enjeux pour les années à venir, aidée en cela par le PNSO2 dont elle adopte la structuration.

In this work were elaborated thin films of Zinc Magnesium Oxide (ZnMgO) by ultrasonic spray pyrolysis. Zn(1-x)Mg(x)O is a wide bandgap compound semiconductor with useful properties for optoelectronic devices, mainly ultraviolet “solar-blind” detectors, as an active layer, and solar cells where it can be used as a buffer layer. The main difficulties related to the elaboration of Zn(1-x)Mg(x)O using solution-based and spray pyrolysis techniques are the wide miscibility gap between MgO and ZnO and the use of toxic and unsafe solvents such as methanol. In this study, we were able to elaborate Zn(1-x)Mg(x)O with varying Mg content up to 70% with water-based solutions only. The difficulty using only water-based solutions is related to the inherent unfavorable properties such as strong hydrogen bonds with high boiling point. However, we managed to optimize the precursors solution concentration, the number of scans, the flow rate, the pressure and the temperature, to obtain homogeneous and good quality films. The solid composition in the thin films was measured using X-ray fluorescence to assess the Mg solubility limit in Zn(1-x)Mg(x)O and its incorporation efficiency. High transmittance of about 90 % in the visible region was obtained in all the films with a very small variation with the thickness, suggesting a highly controlled process of the elaboration. The bandgap and the Urbach energy variation with the composition were investigated and linked to the morphology and structural properties. A miscibility limit of 30 % of Mg was obtained, confirmed by the X-ray fluorescence measurements and correlated to the bandgap variation with the Mg composition extracted from the transmittance spectra analysis. The structural properties were investigated using confocal micro-Raman spectroscopy which permitted to identify the wurtzite structure as the only phase in all the films with composition less than 30 %, with a phase separation occurring beyond this limit. The electrical properties were characterized using the van der Pauw and Hall effect technique using indium to form the ohmic contacts. The n-type carrier concentration dramatically decreases from about 2*10^(19) to 5*10^(15) cm^(-3) when increasing Mg composition from 0 % to 7 %. The thin films become semi-insulating for Mg composition higher than 7 %. The correlation of the electrical results with the optical and structural properties suggests that, in addition to the increase of the bandgap, a compensation mechanism related to the defects introduced in the alloy plays a central role in the decrease in the carrier concentration. The mobility slightly increases with the Mg composition suggesting that the films crystal quality was not significantly degraded by the increase of the magnesium composition in the considered range. The modulation of the conductivity, in addition and partially related to the modulation of the bandgap, is of high interest to the detector or the solar cell device.

Deliverable 6 of the 19ENV09 EMPIR project MetroPEMS

"Summary report on the current state-of-the-art of Exhaust Flow Meter (EFM) calibration procedures, including (i) its associated uncertainty for relevant carrier gases and (ii) its relation to on-road emission tests"