Nicoleta Nicoara

International Iberian Nanotechnology Laboratory

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Sascha Sadewasser

International Iberian Nanotechnology Laboratory

José M. Gómez‐Rodríguez

Universidad Autónoma de Madrid

Javier Méndez

Instituto de Ciencia de Materiales de Madrid

P.M.P. Salomé

University of Aveiro

Deepanjan Sharma

International Iberian Nanotechnology Laboratory

Wolfram Witte

Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg

Philip Jackson

Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg

Dimitrios Hariskos

Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg

J. C. González

Max Planck Institute for Plasma Physics

Joaquim P. Leitão

University of Aveiro

Cooperative Institutions

International Iberian Nanotechnology Laboratory

Centre National de la Recherche Scientifique

Universidad Autónoma de Madrid

University of Luxembourg

Institut des Matériaux Jean Rouxel

Nantes Université

Clinical Academic Center of Braga

University of Minho

Consejo Superior de Investigaciones Científicas

Luxembourg Institute of Science and Technology

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Overall alkaline water electrolysis over active, stable, low loading iridium catalysts sputtered on nickel foam

International Journal of Hydrogen Energy (2024)

Isilda Amorim Natalia C.M. Spera Nicoleta Nicoara Devaraj Ramasamy Diana Alves

Electrolysis of water

10.1016/j.ijhydene.2024.10.306

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Citations (0)

Vacuum‐Healing of Grain Boundaries in Sodium‐Doped CuInSe₂ Solar Cell Absorbers

Advanced Energy Materials (2023)

Finn Babbe Nicoleta Nicoara Harvey Guthrey Nathalie Valle Omar Ramírez

Abstract Alkali metal doping and grain boundaries (GB) have been at the center of attention within the Cu(In,Ga)(S,Se) 2 photovoltaics community for years. This study provides the first experimental evidence that the GB of sodium‐doped CuInSe 2 thin films may undertake reversible oxidation even at room temperature, whereas undoped films may not. The findings are corroborated by cathodoluminescence imaging, secondary ion mass spectrometry, and Kelvin probe force microscopy on air‐exposed films subsequently subject to vacuum. A thermochemical assessment identifies the likely solid–gas equilibria involved. These reactions open new research questions with respect to the beneficial role played by alkali metal dopants in chalcopyrite solar cells and may steer the community toward new breakthroughs.

Cathodoluminescence

10.1002/aenm.202204183

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Citations (11)

Effect of the KF post-deposition treatment on grain boundary properties in Cu(In, Ga)Se2 thin films

Scientific Reports (2017)

Nicoleta Nicoara Thomas Lepetit Ludovic Arzel Sylvie Harel Nicolas Barreau

Abstract Significant power conversion efficiency improvements have recently been achieved for thin-film solar cells based on a variety of polycrystalline absorbers, including perovskites, CdTe, and Cu(In,Ga)Se 2 (CIGS). The passivation of grain boundaries (GBs) through (post-deposition) treatments is a crucial step for this success. For the case of CIGS, the introduction of a potassium fluoride post-deposition treatment (KF-PDT) has boosted their power conversion efficiency to the best performance of all polycrystalline solar cells. Direct and indirect effects of potassium at the interface and interface-near region in the CIGS layer are thought to be responsible for this improvement. Here, we show that also the electronic properties of the GBs are beneficially modified by the KF-PDT. We used Kelvin probe force microscopy to study the effect of the KF-PDT on the CIGS surface by spatially resolved imaging of the surface potential. We find a clear difference for the GB electronic properties: the KF-PDT increases the band bending at GBs by about 70% and results in a narrower distribution of work function values at the GBs. This effect of the KF-PDT on the GB electronic properties is expected to contribute to the improved efficiency values observed for CIGS thin-film solar cells with KF-PDT.

Passivation

Band bending

Cadmium telluride photovoltaics

Deposition

10.1038/srep41361

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Citations (84)

Direct evidence for grain boundary passivation in Cu(In,Ga)Se2 solar cells through alkali-fluoride post-deposition treatments

Nature Communications (2019)

Nicoleta Nicoara Roby Manaligod Philip Jackson Dimitrios Hariskos Wolfram Witte

Abstract The properties and performance of polycrystalline materials depend critically on the properties of their grain boundaries. Polycrystalline photovoltaic materials – e.g. hybrid halide perovskites, copper indium gallium diselenide (CIGSe) and cadmium telluride – have already demonstrated high efficiencies and promise cost-effective electricity supply. For CIGSe-based solar cells, an efficiency above 23% has recently been achieved using an alkali-fluoride post-deposition treatment; however, its full impact and functional principle are not yet fully understood. Here, we show direct evidence for the passivation of grain boundaries in CIGSe treated with three different alkali-fluorides through a detailed study of the nanoscale optoelectronic properties. We determine a correlation of the surface potential change at grain boundaries with the open-circuit voltage, which is supported by numerical simulations. Our results suggest that heavier alkali elements might lead to better passivation by reducing the density of charged defects and increasing the formation of secondary phases at grain boundaries.

Passivation

Cadmium telluride photovoltaics

10.1038/s41467-019-11996-y

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Citations (112)

Built-up AFM tips by metal nanoclusters engineering

Applied Surface Science (2021)

Mariano D. Jiménez‐Sánchez I. Brihuega Nicoleta Nicoara Julio Gómez‐Herrero José M. Gómez‐Rodríguez

The ability to probe tip-sample interactions by Atomic Force Microscopy (AFM) has recently boosted our understanding of the matter at the atomic scale, enabling the study of properties of surfaces and adsorbates which were previously inaccessible. Nevertheless, this sensitivity to forces presents some drawbacks, as the requirement of a sharp tip apex to prevent the loss of spatial resolution due to the existence of long-range interactions. In this work, we have overcome this long-standing challenge by investigating the controlled extraction of single metallic nanoclusters, selectively grown on graphene. Our results show that the successive extraction of cluster allows to grow nanotips, which minimize the long-range tip-sample interactions and greatly enhance the topographic resolution. We have demonstrated that the created nanotips are very stable, which enables exchanging the sample and using the same nanotip to explore different surfaces without loss of resolution. Since metallic clusters of very different materials and sizes can be grown and selectively extracted by AFM, ours work paves also the way to the specific functionalization of AFM-tips to sense a large variety of interactions.

Nanoclusters

Atomic units

Surface Modification

10.1016/j.apsusc.2021.149325

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Citations (3)

Imaging Molecular Orbitals of PTCDA on Graphene on Pt(111): Electronic Structure by STM and First-Principles Calculations

The Journal of Physical Chemistry C (2014)

Antonio J. Martínez‐Galera Nicoleta Nicoara José I. Martínez Yannick J. Dappe José Ortega

The adsorption and growth of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on graphene monolayers epitaxially grown on Pt(111) surfaces is studied by a combination of experimental scanning tunneling microscopy (STM) and spectroscopy (STS) measurements and first-principles density functional theory (DFT) calculations. For submonolayer coverage, until the completion of the first layer, PTCDA molecules form a well-ordered herringbone structure with molecules lying flat on the graphene surface weakly coupled to the Pt(111) substrate. High-resolution STM imaging at different sample biases has allowed the identification of intramolecular features that can be related to the original PTCDA frontier orbitals. Theoretical STM calculations, based on local-orbital DFT, have been carried out on the full PTCDA/graphene/Pt(111) system. The comparison of theoretical and experimental STM images has allowed us to ascribe the origin of intramolecular features to the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the free PTCDA molecules. Moreover, the experimental STS spectra display well-resolved peaks centered at −2.2 and +1.2 eV in excellent agreement with DFT calculations. This study reveals that the growth and electronic structure of PTCDA retain all of the essential electronic features of the molecular layer upon adsorption on this weakly coupled graphene on Pt(111) surface.

HOMO/LUMO

10.1021/jp500768y

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Citations (52)

Scanning tunneling and photoemission spectroscopies at the PTCDA/Au(111) interface

Organic Electronics (2006)

Nicoleta Nicoara Elisa Román José M. Gómez‐Rodríguez José Á. Martín‐Gago Javier Méndez

Ultraviolet photoelectron spectroscopy

Surface States

XANES

10.1016/j.orgel.2006.03.010

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Citations (108)

Evidence of reversible oxidation at CuInSe₂ grain boundaries

Diego Colombara Deepanjan Sharma Nathalie Valle Tom Wirtz Anastasiya Zelenina

Effects related to alkali metal doping and grain boundaries have puzzled the chalcopyrite photovoltaics community for a long time. This study is the first to report reversible oxidation of grain boundaries in CuInSe ₂ thin films. The phenomenon is observed in sodium-doped films, but not in undoped ones. Cathodoluminescence imaging, secondary ion mass spectrometry and Kelvin probe force microscopy analyses are performed on CuInSe ₂ thin films before and after exposure to vacuum. The findings suggest the existence of yet unidentified solid-gas equilibria. Resolving the nature of such reactions will provide new insights into the mechanism of alkali metal doping and passivation in chalcopyrite solar cells.

Cathodoluminescence

Passivation

10.1109/pvsc40753.2019.8981351

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Scanning tunnelling microscopy and spectroscopy on organic PTCDA films deposited on sulfur passivated GaAs(001)

Journal of Physics Condensed Matter (2003)

Nicoleta Nicoara Óscar Custance Daniel Granados J. M. Garcı́a José M. Gómez‐Rodríguez

Deposition of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on sulfur passivated gallium arsenide S-GaAs(001) surfaces is investigated by scanning tunnelling microscopy and scanning tunnelling spectroscopy. The surface morphology and the film structure are studied for the multilayer growth of the organic molecules. Spectroscopic results for both clean substrate and ordered areas of PTCDA are shown in this work. We have measured I–V plots at different tip–sample distances, avoiding deformation of the organic layer. Under proper experimental conditions, a gap value of 2.2 eV has been measured on PTCDA crystals, in good agreement with the expected value for PTCDA (2.2–2.55 eV).

Deposition

10.1088/0953-8984/15/38/003

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Citations (24)

Evidence for Chemical and Electronic Nonuniformities in the Formation of the Interface of RbF-Treated Cu(In,Ga)Se₂ with CdS

ACS Applied Materials & Interfaces (2017)

Nicoleta Nicoara Thomas Kunze Philip Jackson Dimitrios Hariskos Roberto Félix

We report on the initial stages of CdS buffer layer formation on Cu(In,Ga)Se2 (CIGSe) thin-film solar cell absorbers subjected to rubidium fluoride (RbF) postdeposition treatment (PDT). A detailed characterization of the CIGSe/CdS interface for different chemical bath deposition (CBD) times of the CdS layer is obtained from spatially resolved atomic and Kelvin probe force microscopy and laterally integrating X-ray spectroscopies. The observed spatial inhomogeneity in the interface's structural, chemical, and electronic properties of samples undergoing up to 3 min of CBD treatments is indicative of a complex interface formation including an incomplete coverage and/or nonuniform composition of the buffer layer. It is expected that this result impacts solar cell performance, in particular when reducing the CdS layer thickness (e.g., in an attempt to increase the collection in the ultraviolet wavelength region). Our work provides important findings on the absorber/buffer interface formation and reveals the underlying mechanism for limitations in the reduction of the CdS thickness, even when an alkali PDT is applied to the CIGSe absorber.

Chemical bath deposition

Buffer (optical fiber)

Characterization

Rubidium

Ultraviolet

10.1021/acsami.7b12448

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Citations (26)