Framework structure materials in photovoltaics based on perovskites 3D

The inorganic and hybrid organic / inorganic perovskites based on lead halide and derived materials (alloys) having the formula ABX3 are emerging as a new and innovative family of absorber materials for the conversion of solar energy into electricity in photovoltaic systems. Thanks to their composition, perovskites and derivatives have exceptional optical, electrical and structural properties with high absorption of light in the visible solar spectrum and good mobility of charge carriers generated by photons facilitating the extraction of electric current. Due to these important properties, perovskite solar cells combine a high efficiency of conversion of light into electricity with great ease of preparation and synthesis at very low costs via simple deposition techniques. In this article we review the structural and optoelectronic properties of perovskites 3D exhibiting photovoltaic properties, we are also interested in the operating principle of perovskite-based solar cells, charge transport materials and associated architectures. Simple fabrication techniques and issues with stability and hysteresis are also discussed.

Graphene-titanate photocatalyst and its use in an air purifying device - prototype demonstration in operational environment

Volatile organic compounds constitute a group of dangerous air pollutants, which can be eliminated by the photocatalytic route. In this work we demonstrated the hydrothermal synthesis of photocatalytic composite CTO-RGO based on copper titanate and reduced graphene oxide. The material is composed of three phases namely rutile, tenorite and reduced graphene oxide, and it shows absorption in a broad range of light (ultraviolet and visible light). CTO-RGO showed an excellent photocatalytic activity in a laboratory scale experiment. Therefore it has been used as an active material in air purifying devices. A prototype was tested in operational environments such as apartment, fitness center and industrial places. Obtained results confirmed the significant decrease of VOC level due to photocatalytic degradation of pollutants.

Resistance Switching Effect in Octahedral framework oxide

Resistive Random-Access Memories (ReRAM) are an alternative way to create new memory devices. This is physically possible due to the existence in the material, of two resistive states clearly discreditable, as a function of voltage value and polarity first parameter under control to pass from one state to another one. However, the mechanism of the resistance switching is not simple and is under debate. We present in the present chapter all the factors entering in the switching process in tetragonal tungsten bronze (TTB) type structure oxide thin films deposited by PLD technique onto MgO or STO substrates. Results show that GdK2Nb5O15 (GKN) thin films deposited on MgO and STO substrates are resistively switchable. It was found that the nature of the substrate strongly affects the resistance ratio: GKN on SRO/LSCO/MgO showed a large hysteresis compared to GKN on SRO/STO. Substrate effect and oxygen vacancy on resistance switching in GKN thin film were studied in the same experimental conditions. The study of resistance switching in the GKN/MgO and GKN/STO thin films has confirmed that for low voltages, below the threshold value of 1.3 V, the electric transport is dominated by the formation of a Schottky type barrier, which allows a minimum leakage current. Resistance switching in GKN is attributed to the oxygen vacancies migration which can be controlled by the substrate or the frequency sweep.

BaTiO3 films for multilayer devices by tape casting

The diversity of the applicational scope of modern printed electronics relentlessly requires the improvement of operational properties simultaneously with reducing the overall dimensions of devices. One of the most effective ways to overcome this major obstacle is the reduction of functional layers thickness in respect to the size of the device. In the present article, we are discussing a simple way of practical implementation of miniaturization concept through the application of a well-known high-productive industrial method of tape casting for obtaining thin nanostructured ceramic layers based on BaTiO3 nanopowders for MLCC. Using of nanosized powders per se imply a new approach of developing suspensions with suitable rheology for tape casting. We demonstrate, that a length of polymer molecule defines the size of floccules and therefore influences the thickness and surface quality of tape casted films. A certain nanopowder/polymer ratio contributes to the formation of the tapes with the surface roughness comparable with the size of one nanoparticle (20-25 nm). Moreover, it was established that developed suspensions are extremely sensitive to temperature changes. Lowering the temperature significantly affects the flow character of suspension and thus the thickness of casted tapes. Considering this fact, we propose an effective self-developed pre-cooling method of nanopowder suspension casting, which allows obtaining extremely thin and smooth tapes with a thickness of less than 1 µm and surface roughness of 20–25 nm by tape casting method.

Properties of Na 0.5Bi0.5TiO3 and Na0.5Bi0.5 TiO3-based single crystals

Most studies of ferroelectric materials were focused on polycrystalline ceramics. However, it is difficult to improve their properties significantly (particularly piezoelectric one) due to grain/grain boundaries, compositional homogeneity, isotropic characteristics, and structural defects. It is commonly accepted that single crystals often have better piezoelectric behavior and less structural defects than ceramics. In this paper, we provide the processing technology and properties of lead-free Na0.5Bi0.5TiO3 and Na0.5Bi0.5TiO 3-based single crystals. #FERROELECTRICS #NBT_SINGLE_CRYSTALS #FLUX_METHOD #CZOCHRALSKI_METHOD #DIELECTRIC_PROPERTIES

Amorphous materials based on perovskite ferroelectrics

The methods of preparation, as well as the structure and most relevant physical properties of amorphous materials based on ferroelectrics with perovskite structure are reviewed. The theoretical basis for the possibility of ferroelectricity in non-crystalline solids is discussed. The structural relaxation in a glassy state and the crystallization processes leading to the formation of a ferroelectric phase are considered. The structure and physical properties of thin-film amorphous ferroelectrics that demonstrate noticeable differences from the properties of the same materials in bulk state are discussed separately

Hybrid perovskites: Charge carrier recombination effects in photovoltaic devices

Hybrid lead halide perovskites emerged at the beginning of 2010s decade as one of the most promising materials for photovoltaic applications. Easy and low-cost solution-based fabrication processes can be used, obtaining perovskite solar cells (PSCs) with efficiencies above 20%. However, there still are some major issues to overcome, like stabiliddty, and the general understanding of the recombination mechanisms resHybrid lead halide perovskites emerged at the beginning of 2010s decade as one of the most promising materials for photovoltaic applications. Easy and low-cost solution-based fabrication processes can be used, obtaining perovskite solar cells (PSCs) with efficiencies above 20%. However, there still are some major issues to overcome, like stability, and the general understanding of the recombination mechanisms results particularly puzzling. In this chapter, an analysis is provided on most recent research results about the different mechanisms, location and relationships of charge carrier recombination in PSCs. After introducing the theoretical framework, including the main transport equations and relations with luminescence techniques, the radiative and non-radiative natures of recombination are commented and compared in terms of main contributions. Also, the effects of changing the perovskite composition and morphology are surveyed. The location of the recombination processes, whether in the bulk material or towards the interface, are tackled, as well as related features with the current-voltage hysteresis. On the latter, and along the complete chapter, the dual ionic-electronic conductivity of hybrid lead halide perovskites is particularly attended. ults particularly puzzling. In this chapter, an analysis is provided on most recent research results about the different mechanisms, location and relationships of charge carrier recombination in PSCs. After introducing the theoretical framework, including the main transport equations and relations with luminescence techniques, the radiative and non-radiative natures of recombination are commented and compared in terms of main contributions. Also, the effects of changing the perovskite composition and morphology are surveyed. The location of the recombination processes, whether in the bulk material or towards the interface, are tackled, as well as related features with the current-voltage hysteresis. On the latter, and along the complete chapter, the dual ionic-electronic conductivity of hybrid lead halide perovskites is particularly attended. ybrid lead halide perovskites emerged at the beginning of 2010s decade as one of the most promising materials for photovoltaic applications. Easy and low-cost solution-based fabrication processes can be used, obtaining perovskite solar cells (PSCs) with efficiencies above 20%. However, there still are some major issues to overcome, like stability, and the general understanding of the recombination mechanisms results particularly puzzling. In this chapter, an analysis is provided on most recent research results about the different mechanisms, location and relationships of charge carrier recombination in PSCs. After introducing the theoretical framework, including the main transport equations and relations with luminescence techniques, the radiative and non-radiative natures of recombination are commented and compared in terms of main contributions. Also, the effects of changing the perovskite composition and morphology are surveyed. The location of the recombination processes, whether in the bulk material or towards the interface, are tackled, as well as related features with the current-voltage hysteresis. On the latter, and along the complete chapter, the dual ionic-electronic conductivity of hybrid lead halide perovskites is particularly attended.

Naturally Layered Aurivillius Phases: Flexible Scaffolds for the Design of Multiferroic Materials

The Aurivillius layer-structures, described by the general formula Bi2O2(Am-1BmO3m+1), are naturally 2-dimensionally nanostructured. They are very flexible frameworks for a wide variety of applications, given that different types of cations can beaccommodated both at the A- and B-sites. In this review article, we describe how the Aurivillius phases are a particularly attractive class of oxides for the design of prospective single phase multiferroic systems for multi-state data storage applications, as they offer the potential to include substantial amounts of magnetic cations within a strongly ferroelectric system. The ability to vary m yields differing numbers of symmetrically distinct B-site locations over which the magnetic cations can be distributed and generates driving forces for cation partitioning and magnetic ordering. We discuss how out-of-phase boundary and stacking fault defects can further influence local stoichiometry and the extent of cation partitioning in these intriguing material systems.

Hybrid organic-inorganic perovskites: a spin-off of oxidic perovskites

ABX3 compounds with perovskite structure have been intensively and extensively studied in the last decades in view of their structural richness and amazing variety of interesting properties, such as piezoelectricity, ferroelectricity, ferromagnetism, superconductivity, magnetoresistance, multiferroicity, etc. In this chapter, we recompile well-established chemical and structural concepts in pure inorganic perovskites (mainly oxidic perovskites), and extend them to the young family of hybrid organic-inorganic perovskites. Our final goal is to help understanding the relationships among composition, crystal structure and properties in this new family of compounds, for inspiring further the design of novel materials.

Structural distortions of orthorhombic RFeO3 and RMnO3

We will address in detail the structural distortions responsible for the symmetry lowering of the ideal cubic Pm-3m perovskite to the orthorhombic Pnma structure of RFeO3 and RMnO3 (R = trivalent rare-earth cation), important to the stabilization of the different magnetic and multiferroic phases in these materials. We will also show how the Amplimodes tool of Bilbao Crystallographic Server is useful in quantifying these distortions and establish which phonons can be used as probes of both the octahedra tilting and deformation.