Centre for Nuclear Sciences and Technologies

Funder

Organizational Unit

Publications

In-Depth Inhomogeneities in CIGS Solar Cells: Identifying Regions for Performance Limitations by PIXE and EBS

Publication . Corregidor, V.; Barreiros, M. Alexandra; Salomé, P.M.P.; Alves, L. C.

ABSTRACT: When considering materials to be used as active layers in solar cells, an important required parameter is the proper knowledge of their elemental composition. It should be heavily controlled during growth in order to obtain the desired band gap and to decrease the recombination defects and then increase the solar cell electrical performance. Ion beam analytical (IBA) techniques and, in particular, particle-induced X-ray emission (PIXE) and elastic backscattering spectrometry (EBS) are quite suitable to determine the thickness and composition of such active layers. Furthermore, if these techniques are performed using a nuclear microprobe, lateral and in-depth inhomogeneities can be clearly observed from 2D maps. In many cases, composition variations can be detected from the classical 2D maps obtained from the PIXE spectra. In this work, it is shown how the in-depth variations can also be studied when considering 2D maps reconstructed from the EBS spectra. Such variations are derived from processing conditions and can be related to (i) composition, (ii) thickness, (iii) roughness, and (iv) other nontrivial issues. Examples obtained on Cu(In,Ga)Se-2-based cells are presented and discussed. Furthermore, the combination of IBA techniques such as PIXE and EBS is shown to be a competitive and alternative method to the more used and established techniques such as X-ray fluorescence for checking the average composition of the solar cell active layers or secondary ion mass spectroscopy for determination of the elemental depth profile.

2021-07Journal article

Embargoed access

Hybrid molecular dynamic Monte Carlo simulation and experimental production of a multi-component Cu-Fe-Ni-Mo-W alloy

Publication . Dias, Marta; Almeida Carvalho, Patricia; Gonçalves, António Pereira; Alves, E.; Correia, J.B.

ABSTRACT: High-entropy alloys are a class of materials intensely studied in the last years due to their innovative properties. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. The Cu-Fe-Ni-Mo-W multicomponent alloy was studied using a combination of simulation and experimental production to test the possibility of formation of a simple solid solution. Therefore, Molecular Dynamics and hybrid Molecular Dynamic/Monte Carlo simulations from 10K up to the melting point of the alloy were analyzed together with the experimental production by arc furnace and powder milling. The Molecular Dynamics simulations starting with a bcc type-structure show the formation of a singlephase bcc solid solution type-structure, whereas using Monte Carlo one, generally produced a two-phase mixture. Moreover, the lowest potential energy was obtained when starting from a fcc type-structure and using Monte Carlo simulation giving rise to the formation of a bcc Fe-Mo-W phase and a Cu-Ni fcc type-structure. Dendritic and interdendritic phases were observed in the sample produced by arc furnace while the milled powder evidence an separation of two phases Cu-Fe-Ni phase and W-Mo type-structures. Samples produced by both methods show the formation of bcc and a fcc type-structures. Therefore, the Monte Carlo simulation seems to be closer with the experimental results, which points to a two-phase mixture formation for the Cu-Fe-Ni-Mo-W multicomponent system.

2023-10Journal article

Open access

Simulation and study of the milling parameters on CuFeTaTiW multicomponent alloy

Publication . Martins, Ricardo; Gonçalves, António Pereira; Correia, J.B.; Galatanu, Andrei; Alves, E.; Dias, Marta

ABSTRACT: The CuFeTaTiW multicomponent alloy has been devised as an interlayer thermal barrier in nuclear fusion re-actors. In order to predict the phase constitution of this alloy, two different lines of work were performed: (a) simulation using Molecular dynamics and Monte Carlo and (b) study of the influence of mechanical alloying parameters on the structures formed. The simulation results show that the most stable structure is achieved starting from a bcc type-structure and using Monte Carlo simulation. In fact, in these conditions the separation into two bcc phases Fe-Ta-W and Cu-Ti is predicted at room temperature. However, the experimental preparation of the materials with mechanical alloying revealed that from 2 h of milling a single bcc phase is formed. The structure of the milled powder was not much influenced by the amount of the process control agent and the by the size of the W starting particles, but generally there was formation of Ta2H from the reaction between the powders and the process control agent.

2024-03Journal article

Open access

Thermoelectric Properties of Tetrahedrites Produced from Mixtures of Natural and Synthetic Materials

Publication . Santos, Beatriz; Esperto, Luís; Figueira Vasques, Isabel; Mascarenhas, João; Lopes, E.B.; Salgueiro, Rute; Silva, Teresa; Correia, Jose B.; de Oliveira, Daniel Pipa Soares; Pereira Gonçalves, Antonio; Neves, Filipe

ABSTRACT: Thermoelectric materials have considerable potential in the mitigation of the global energy crisis, through their ability to convert heat into electricity. This study aims to valorize natural resources, and potentially reduce production costs, by incorporating tetrahedrite-tennantite (td) ores from the Portuguese Iberian Pyrite Belt into synthetic samples. The ore samples were collected in a mine waste at Barrig & atilde;o and as "dirty-copper" pockets of ore from the Neves Corvo mine. Subsequently, high-energy ball milling and hot pressing were employed in the production of thermoelectric materials. These are characterized by XRD, SEM/EDS, and thermoelectrical properties. The complete dissolution of the dump material sulfides with the synthetic tetrahedrite constituents led to an increase in the amount of the tetrahedrite-tennantite phase, which was made up of a tetrahedrite-tennantite-(Fe) solid solution. The thermoelectric characterization of these materials is provided, revealing that most of the combined synthetic ore samples displayed better results than the pristine tetrahedrite, mostly due to higher Seebeck coefficient values. Furthermore, the best thermoelectric performance is achieved with 10% of ore, where a power factor of 268 mu W.K-2.m-1 is reached at room temperature.

2025-03Journal article

Open access