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RL1: Sustainable Energy Conversion & Storage Systems

In the field of organic photovoltaics (PV), an alternative spectral splitting device concept, called RAINBOW, has been proposed, in which various individual junctions with cascading bandgaps are laid side by side. Each lateral sub-cell receives a fraction of the solar spectrum that matches the main absorption band of the given semiconductor. For a two-junction tandem it was already shown that this geometry can lead to a relative improvement in efficiency of ca. 50% with respect to the best sub-cell. In addition, a patented multi-purpose spectrum-on-demand light source (SOLS) has been developed, for which the EmErgEnt'23 Prize of the Clúster de l'Energia Eficient de Catalunya (CEEC) was awarded. This spectral shaper illumination device is expected to accelerate material screening and device optimization for emergent PV technologies.  Regarding complex oxides (e.g. La0.7Sr0.3MnO3) for PV applications, the chemical synthesis of thin films has been further developed for the fabrication of p-type transparent conducting electrodes and the role of sacrificial-layer composition has been studied for the realization of free-standing, flexible oxide membranes.

Soft nanoimprint lithography has been successfully employed to assemble versatile hybrid perovskite nanocrystals (NCs) into 2D-chiral metasurfaces, which exhibit remarkable asymmetry factors of 0.16 for the emission of circularly polarized light. This scalable approach to produce chiral luminescent thin films paves the way for the seamless production of bright chiral light sources.

Regarding thermal transport, the methodology of contactless frequency-domain thermoreflectance (FDTR) has been further extended to measure the in-plane thermal diffusivity of anisotropic materials, using a spatial offset between the 1D optical heat source and the probe beam. This method has been patented, resulting in a proof-of-concept project and the signing of a co-development contract with LINSEIS, a leading European company in the manufacture of commercial thermal-transport setups.

Battery research has a focus on synthesis and characterization of electrode materials for both Li-ion and post-Li ion batteries. Most recent work includes the study of Prussian Blue Analogues for Mg and Ca batteries and efforts on operando and synchrotron based techniques in collaboration with ALBA, where a joint laboratory has been established in the framework of the PTI Transener+. Organic positive electrodes are excellent low-cost, sustainable alternatives to inorganic materials and as such, polyimide was tested in mono and divalent cells, obtaining improved electrochemical performances in Mg-based electrolytes. Furthermore, wireless bipolar electrochemistry was successfully used to generate a substantial decrease in resistance of energy storage devices.

Considering laser-based materials processing techniques, especial efforts were made for increasing the technological readiness level (one industrial secret was registered). Besides, new approaches such as reactive inverse matrix-assisted pulsed-laser evaporation (RIMAPLE) and liquid phase laser synthesis, were advanced for the production of complex hybrid photo-catalysts for solar-based wastewater treatment and water-splitting hydrogen generation.

2D-chiral metasurfaces fabricated using nanoimprint lithography to produce chiral gammadion arrays with perovskite NCs

Mendoza-Carreño, José; Molet, Pau; Otero-Martínez, Clara; Alonso, María Isabel; Polavarapu, Lakshminarayana; Mihi, Agustín

Advanced Materials 2023, 35, 2210477.


The production of chiral perovskites has become an active field of research for its promising applications in optics, chemistry, or biology. Typically, chiral halide perovskites are obtained by the incorporation of different chiral moieties in the material. Unfortunately, these chemically modified perovskites have demonstrated moderate values of chiral photoluminescence (PL) so far. Here, a general and scalable approach is introduced to produce chiral PL from arbitrary nanoemitters assembled into 2D-chiral metasurfaces. The fabrication via nanoimprinting lithography employs elastomeric molds engraved with chiral motifs covering millimeter areas that are used to pattern two types of unmodified colloidal perovskite nanocrystal (NC) inks: green-emissive CsPbBr3 and red-emissive CsPbBr1I2. The perovskite 2D-metasurfaces exhibit remarkable PL dissymmetry factors (glum) of 0.16 that can be further improved up to glum of 0.3 by adding a high-refractive-index coating on the metasurfaces.

2D-chiral metasurfaces fabricated using nanoimprint lithography to produce chiral gammadion arrays with perovskite NCs

Gibert-Roca, Martí; Casademont-Viñas, Miquel; Liu, Quan; Vandewal, Koen; Goñi, Alejandro R.; Campoy-Quiles, Mariano

Advanced Materials 2023, 2212226


While multi-junction geometries have the potential to boost the efficiency of organic solar cells, the experimental gains yet obtained are still very modest. This work proposes an alternative spectral splitting device concept in which various individual semiconducting junctions with cascading bandgaps are laid side by side, thus the name RAINBOW. Each lateral sub-cell receives a fraction of the spectrum that closely matches the main absorption band of the given semiconductor. Simulations are used to develop design rules to identify the important material and device properties of each RAINBOW sub-cell. With the aid of a custom-built setup that generates spectrally spread sunlight on demand, the simulations are experimentally validated, showing that this geometry can lead to a reduction in thermalization losses and an improvement in light harvesting, which results in a relative improvement in efficiency of 46.6% with respect to the best sub-cell. Finally, a working proof-of-concept monolithic device consisting of two sub-cells deposited from solution on the same substrate is fabricated, thus demonstrating the feasibility and the potential of the RAINBOW solar cell concept.

2D-chiral metasurfaces fabricated using nanoimprint lithography to produce chiral gammadion arrays with perovskite NCs

Salles, Pol; Machado, Pamela; Yu, Pengmei; Coll, Mariona

Chemical Communications 2023, 59, 13820-13830


Oxides offer unique physical and chemical properties that inspire rapid advances in materials chemistry to design and nanoengineer materials compositions and implement them in devices for a myriad of applications. Chemical deposition methods are gaining attention as a versatile approach to develop complex oxide thin films and nanostructures by properly selecting compatible chemical precursors and designing an accurate cost-effective thermal treatment. Here, upon describing the basics of chemical solution deposition (CSD) and atomic layer deposition (ALD), some examples of the growth of chemically-deposited functional complex oxide films that can have applications in energy and electronics are discussed. The suitability of these techniques to prepare freestanding membranes of complex oxides is presented, which can significantly expand their applications.

2D-chiral metasurfaces fabricated using nanoimprint lithography to produce chiral gammadion arrays with perovskite NCs

Xu, Kai; Guo, Jiali; Raciti, Grazia; Goñi, Alejandro R.; Alonso, M. Isabel; Borrisé, Xavier; Zardo, Ilaria; Campoy-Quiles, Mariano; Reparaz, Juan Sebastián

International Journal of Heat and Mass Transfer 2023, 214, 124376


We present an innovative contactless method suitable to study in-plane thermal transport based on beam-offset frequency-domain thermoreflectance using a 1D heat source with uniform power distribution. Advantages of the 1D source, as compared to typically used point-like heat sources, are: (i) A slower spatial decay of the temperature field in the direction perpendicular to the line-shaped heat source, allowing to probe the temperature field at larger distances from the heater, hence, enhancing the sensitivity to in-plane thermal transport; (ii) the frequency range of interest is typically < 100 kHz. This rather low frequency range allows the study of materials without the need of a metallic transducer and with almost no influence of the penetration depth of the pump and probe beams on the thermal phase lag. We also show that for the case of a harmonic thermal excitation source, the phase lag between the thermal excitation and thermal response of the sample exhibits a linear dependence with their spatial offset, where the slope is proportional to the inverse of the thermal diffusivity of the material.

2D-chiral metasurfaces fabricated using nanoimprint lithography to produce chiral gammadion arrays with perovskite NCs

Black, Ashley P.; Sorrentino, Andrea; Fauth, François; Yousef, Ibraheem; Simonelli, Laura; Frontera, Carlos; Ponrouch, Alexandre; Tonti, Dino; Palacín, M. Rosa

Chemical Science 2023, 14, 1641-1665.


Synchrotron radiation based techniques are powerful tools for battery research and allow probing a wide range of length scales, with different depth sensitivities and spatial/temporal resolutions. Operando experiments enable characterization during functioning of the cell and are thus a precious tool to elucidate the reaction mechanisms taking place. In this perspective, the current state of the art for the most relevant techniques (scattering, spectroscopy, and imaging) is discussed together with the bottlenecks to address, either specific for application in the battery field or more generic. Given the recent evolution in the operando experimentation, accelerated progress is expected in the years to come, which should in turn foster battery performance improvements.

2D-chiral metasurfaces fabricated using nanoimprint lithography to produce chiral gammadion arrays with perovskite NCs

Ma, Zheng; Fuentes-Rodriguez, Laura; Tan, Zhengwei; Pellicer, Eva; Abad, Llibertat; Herrero-Martín, Javier; Menéndez, Enric; Casañ-Pastor, Nieves; Sort, Jordi.

Nature Communications 2023, 14, 6486.


Modulation of magnetic properties through voltage-driven ion motion and redox processes, i.e., magneto-ionics, is a unique approach to control magnetism with electric field for low-power memory and spintronic applications. So far, magneto-ionics has been achieved through direct electrical connections to the actuated material. Here we evidence that an alternative way to reach such control exists in a wireless manner. Induced polarization in the conducting material immersed in the electrolyte, without direct wire contact, promotes wireless bipolar electrochemistry, an alternative pathway to achieve voltage-driven control of magnetism based on the same electrochemical processes involved in direct-contact magneto-ionics. These results represent a fundamental breakthrough that may inspire future device designs for applications in bioelectronics, catalysis, neuromorphic computing, or wireless communications.

RL2: Superconducting Materials for Emerging Technologies

This Research Line is devoted to deploy unique know-how in superconducting materials and their use in emerging areas of energy, efficient ICT, high energy physics and astrophysics. In particular, our effort is concentrated in three main aspects. Firstly, in developing high-throughput, low-cost growth methods for Coated Conductors (CC) with engineered properties to approach theoretical limits. Also, in investigating superconducting electronic functionalities based on controlling properties of cuprates for ICT and impelling ultrasensitive Transition Edge Sensors (TES) as single photon and phonon detectors. Finally, in customizing CC materials for adequate integration in large scale systems (energy and high energy physics).

Our breakthrough in the development of the Transient Liquid Assisted growth (TLAG) process of cuprates at 100-1000 nm/s growth rates is now fully exploited in the in-situ growth platform at ALBA synchrotron, including the analysis of compositional gradient samples also in collaboration with Kyushu University. Now we have extended the feasibility of this approach to films prepared by Pulsed Laser Deposition, additionally to Chemical Solution Deposition. Also, new emerging ideas were initiated for its use in superconducting joints also involving differentiated oxygenation studies to reach large vortex pinning in the overdoped state.

In the investigation of electronic functionalities, nonlinear optical signatures of quantum phase transitions in the high-temperature superconductor YBCO have been investigated through magneto-transport and high harmonic generation technologies. Manipulation of the superconducting order parameter and electromigration effects were explored in cuprate high-temperature superconductors. In addition, in the framework of the European CHIST-ERA project, on-chip magnetic metasurfaces with efficient control of magnetic fields have been explored for boosting the sensitivity and efficiency of magnetic sensors and functional devices

Besides, in 2023 we worked on electrothermal modelling and noise analysis of TES for X-ray detection, as well as on determining their transition mechanisms. Also, within a project aimed at developing TESs for low-mass dark matter direct detection we started optimization of W films with very low Tc, and worked on the understanding of the decay processes suffered by the created phonons prior to their detection by the TES.

Our scouting activities in customization of CC has led to identified the best architecture to increase the electrical grid protection against short circuits by using surface modified CC in superconducting devices. Additionally, our consolidated collaboration with CERN in the development of low surface impedance superconducting coatings has expanded to high gradient electric fields and high magnetic field studies for accelerators and dark matter search.

Field quality and surface resistance studies of a superconducting REBa2Cu3O7−x - Cu hybrid coating for the FCC beam screen

Telles, G.; Romanov, A.; Calatroni, S.; Granados, X.; Puig, T.; Gutierrez, J.Nature Communications 2023, 14, 6486.

RE(=Y, Gd, Eu)Ba2Cu3O7−x  proposed as a low-surface impedance coating for the beam screen of a circular collider. Persistent currents in the superconductor will degrade the magnetic field homogeneity inside the beam chamber. We have explored the possibility of using a highly conductive hybrid coating made of Cu and REBa2Cu3O7−x. This decreases the surface impedance when compared to that of pure copper, while maintaining high magnetic field quality inside the beam screen chamber.

Transient Liquid Assisted Growth of Superconducting YBa2Cu3O7-x Films Based on Pulsed Laser Deposition

Queraltó, A.; Sieger, M.; Gupta, K.; Meledin, A.; Barusco, P.; Saltarelli, L.; de Palau, M.; Granados, X.; Obradors, X.; Puig, T.

Investigation of the integration of transient liquid-assisted growth (TLAG) approach for epitaxial YBa2Cu3O7−x (YBCO) films by physical deposition methodologies. Highly flat and amorphous YBCO precursor films were deposited by PLD at temperatures below 400 °C on single-crystalline SrTiO3 (STO) and LaMnO3 (LMO)/STO.

Microscale Metasurfaces for On-Chip Magnetic Flux Concentration

Fourneau, E., Arregi, J. A., Barrera, A., Nguyen, N. D., Bending, S., Sanchez, A., Uhlíř, V., Palau, A., Silhanek, A. V.

The effects of downscaling magnetic metamaterials for on-chip integration is investigated. The influence of the non-linear magnetic response of the ferromagnetic components, their magnetic irreversibility, the formation of magnetic domains, as well as the effects of geometry and size of the devices are scrutinized.

A Sulfurization method for creating the buffer-layers Current Flow Diverter architecture in REBa2Cu3O7 coated conductors

Barusco, P.; Giguere, J.; Lacroix, C.; Sirois, F.; Granados, X.; Puig, T.; Obradors, X.

The current flow diverter (CFD) is a known concept that has proven to effectively reduce the probability of destructive hot spots in REBa2Cu3O7 coated conductors (CCs) by boosting the normal zone propagation velocity. The implementation of this concept requires additional steps in a fabrication process that is already complex and has struggled to find a simple reel-to-reel fabrication method.