Increasing the Performance and Stability of Red-Light-Emitting Diodes Using Guanidinium Mixed-Cation Perovskite Nanocrystals

Halide perovskite nanocrystals (PNCs) exhibit growing attention in optoelectronics due to their fascinating color purity and improved intrinsic properties. However, structural defects emerging in PNCs progressively hinder the radiative recombination and carrier transfer dynamics, limiting the performance of light-emitting devices. In this work, we explored the introduction of guanidinium (GA⁺) during the synthesis of high-quality Cs_1-xGA_xPbI₃ PNCs as a promising approach for the fabrication of efficient bright-red light-emitting diodes (R-LEDs). The substitution of Cs by 10 mol % GA allows the preparation of mixed-cation PNCs with PLQY up to 100% and long-term stability for 180 days, stored under air atmosphere and refrigerated condition (4 °C). Here, GA⁺ cations fill/replace Cs⁺ positions into the PNCs, compensating intrinsic defect sites and suppressing the nonradiative recombination pathway. LEDs fabricated with this optimum material show an external quantum efficiency (EQE) near to 19%, at an operational voltage of 5 V (50-100 cd/m²) and an operational half-time (t₅₀) increased 67% respect CsPbI₃ R-LEDs. Our findings show the possibility to compensate the deficiency through A-site cation addition during the material synthesis, obtaining less defective PNCs for efficient and stable optoelectronic devices.

2D-Self-Assembled Organic Materials in Undoped Hole Transport Bilayers for Efficient Inverted Perovskite Solar Cells

Interfaces between photoactive perovskite layer and selective contacts play a key role in the performance of perovskite solar cells (PSCs). The properties of the interface can be modified by the introduction of molecular interlayers between the halide perovskite and the transporting layers. Herein, two novel structurally related molecules, 1,3,5-tris(α-carbolin-6-yl)benzene (TACB) and the hexamethylated derivative of truxenotris(7-azaindole) (TTAI), are reported. Both molecules have the ability to self-assemble through reciprocal hydrogen bond interactions, but they have different degrees of conformational freedom. The benefits of combining these tripodal 2D-self-assembled small molecular materials with well-known hole transporting layers (HTLs), such as PEDOT:PSS and PTAA, in PSCs with inverted configuration are described. The use of these molecules, particularly the more rigid TTAI, enhanced the charge extraction efficiency and reduced the charge recombination. Consequently, an improved photovoltaic performance was achieved in comparison to the devices fabricated with the standard HTLs.

Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

The kinetics of light emission in halide perovskite light-emitting diodes (LEDs) and solar cells is composed of a radiative recombination of voltage-injected carriers mediated by additional steps such as carrier trapping, redistribution of injected carriers, and photon recycling that affect the observed luminescence decays. These processes are investigated in high-performance halide perovskite LEDs, with external quantum efficiency (EQE) and luminance values higher than 20% and 80 000 Cd m^-2 , by measuring the frequency-resolved emitted light with respect to modulated voltage through a new methodology termed light emission voltage modulated spectroscopy (LEVS). The spectra are shown to provide detailed information on at least three different characteristic times. Essentially, new information is obtained with respect to the electrical method of impedance spectroscopy (IS), and overall, LEVS shows promise to capture internal kinetics that are difficult to be discerned by other techniques.

Unusual Spectrally Reproducible and High Q-Factor Random Lasing in Polycrystalline Tin Perovskite Films

An unusual spectrally reproducible near-IR random lasing (RL) with no fluctuation of lasing peak wavelength is disclosed in polycrystalline films of formamidinium tin triiodide perovskite, which have been chemically stabilized against Sn²⁺ to Sn⁴⁺ oxidation. Remarkably, a quality Q-factor as high as ≈10⁴ with an amplified spontaneous emission (ASE) threshold as low as 2 µJ cm^-2 (both at 20 K) are achieved. The observed spectral reproducibility is unprecedented for semiconductor thin film RL systems and cannot be explained by the strong spatial localization of lasing modes. Instead, it is suggested that the spectral stability is a result of such an unique property of Sn-based perovskites as a large inhomogeneous broadening of the emitting centers, which is a consequence of an intrinsic structural inhomogeneity of the material. Due to this, lasing can occur simultaneously in modes that are spatially strongly overlapped, as long as the spectral separation between the modes is larger than the homogeneous linewidth of the emitting centers. The discovered mechanism of RL spectral stability in semiconductor materials, possessing inhomogeneous broadening, opens up prospects for their practical use as cheap sources of narrow laser lines.

Balanced change in crystal unit cell volume and strain leads to stable halide perovskite with high guanidinium content

Up-to-date studies propose that strain in halide perovskites is one of the key factors that determine a device's efficiency and stability. Here, we show a systematic approach to characterize the phenomenon in the standard methylammonium lead iodine (MAPbI3) perovskite system by: (i) the substitution of some MA by guanidinium (Gu); (ii) the incorporation of PbS quantum dot (QD) additives and (iii) addition of both Gu and PbS at the same time. We studied the effect of these incorporations on the film strain and crystal cell unit volume, and on the solar cell device efficiency and stability. Gu cations and PbS QDs affect the strain, the former due to the relatively large dimensions of Gu, and the latter due to the lattice matching parameters. With the control of Gu and PbS QD content, higher performance and longer solar cell stability are obtained. We demonstrated that the presence of Gu and PbS QDs alters the structure of perovskite, in terms of modification of the unit cell volume and strain. The greater size of Gu cations produces a MAPbI3 unit cell volume expansion as Gu is incorporated, modifying the strain from compressive to tensile. PbS QDs aid Gu incorporation, producing a unit cell volume expansion. In the case of 15% mol Gu incorporation, the addition of PbS QDs modifies strain from compressive to tensile, limiting the deleterious effect. At the same time the unit cell volume is less affected, increasing the solar cell stability. Our work shows that the control of compressive strain and the unit cell volume expansion lead to a 50% increase in T 80, the time in which the PCE decreases to 80% of its original value, increasing the T 80 value from 120 to 187 days under air conditions. Moreover it highlights the importance of exploiting not only the control of the strain induced by internal component, the cation, but also the strain induced by the external component, the QD, associated instead with critical volume variation of metastable perovskite unit cell volume.

2D PEA2SnI4 Inkjet-Printed Halide Perovskite LEDs on Rigid and Flexible Substrates

Lead-free PEA₂SnI₄-based perovskite LEDs are successfully inkjet-printed on rigid and flexible substrates. Red-emitting devices (λ_max = 633 nm) exhibit, under ambient conditions, a maximum external quantum efficiency (EQE_max) of 1% with a related brightness of 30 cd/m² at 10 mA/cm².

Tin perovskite solar cells with >1,300 h of operational stability in N2 through a synergistic chemical engineering approach

Despite the promising properties of tin-based halide perovskites, one clear limitation is the fast Sn⁺² oxidation. Consequently, the preparation of long-lasting devices remains challenging. Here, we report a chemical engineering approach, based on adding Dipropylammonium iodide (DipI) together with a well-known reducing agent, sodium borohydride (NaBH₄), aimed at preventing the premature degradation of Sn-HPs. This strategy allows for obtaining efficiencies (PCE) above 10% with enhanced stability. The initial PCE remained unchanged upon 5 h in air (60% RH) at maximum-power-point (MPP). Remarkably, 96% of the initial PCE was kept after 1,300 h at MPP in N₂. To the best of our knowledge, these are the highest reported values for Sn-based solar cells. Our findings demonstrate a beneficial synergistic effect when additives are incorporated, highlight the important role of iodide in the performance upon light soaking, and, ultimately, unveil the relevance of controlling the halide chemistry for future improvement of Sn-based perovskite devices.

White light emission from lead-free mixed-cation doped Cs2SnCl6 nanocrystals

We have designed a synthesis procedure to obtain Cs₂SnCl₆ nanocrystals (NCs) doped with metal ion(s) to emit visible light. Cs₂SnCl₆ NCs doped with Bi³⁺, Te⁴⁺ and Sb³⁺ ions emitted blue, yellow and red light, respectively. In addition, NCs simultaneously doped with Bi³⁺ and Te⁴⁺ ions were synthesized in a single run. Combination of both dopant ions together gives rise to the white emission. The photoluminescence quantum yields of the blue, yellow and white emissions are up to 26.5, 28, and 16.6%, respectively under excitation at 350, 390, and 370 nm. Pure white-light emission with CIE chromaticity coordinates of (0.32, 0.33) and (0.32, 0.32) at 340 and 370 nm excitation wavelength, respectively, was obtained. The as-prepared NCs were found to demonstrate a long-time stability, resistance to humidity, and an ability to be well-dispersed in polar solvents without property degradation due to their hydrophilicity, which could be of significant interest for wide application purposes.

Supramolecular gating of TADF process in self-assembled nano-spheres for high-resolution OLED applications

Acridine-based donor-acceptor chromophores exhibiting E-type delayed fluorescence were substituted with bis-biuret H-bonding motifs to induce the formation of hollow spheres which can be deposited from solution to form the active component of OLED devices. In solution, the contribution of the delayed component is sensitive to disruption of the aggregates.

Boosting Long-Term Stability of Pure Formamidinium Perovskite Solar Cells by Ambient Air Additive Assisted Fabrication

Due to the high industrial interest for perovskite-based photovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions. The formamidinium lead iodide (FAPI) perovskite α-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells (PSCs) have a dramatic increase of device long-term stability when prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with N-methylpyrrolidone (NMP). The T 80 parameter, the time in which the efficiency drops to 80% of the initial value, increases from 21 (in N2) to 112 days (in ambient) to 145 days if PbS quantum dots (QDs) are introduced as additives in air-prepared FAPI PSCs. Furthermore, by adding methylammonium chloride (MACl) the power conversion efficiency (PCE) reaches 19.4% and devices maintain 100% of the original performance for at least 53 days. The presence of Pb-O bonds only in the FAPI films prepared in ambient conditions blocks the propagation of α- to δ-FAPI phase conversion. Thus, these results open the way to a new strategy for the stabilization in ambient air toward perovskite solar cells commercialization.

Color-Tunable White-Light-Emitting Materials Based on Liquid-Filled Capsules and Thermally Responsive Dyes

Color-tunable white-light-emitting materials are currently attracting much attention because of their potential applications in artificial lighting, sensing, and imaging. However, preparation of these systems from organic emitters is often cumbersome due to the interchromophoric interactions occurring upon solvent drying in the final solid materials, which can be hardly predicted and may lead to detrimental effects. To circumvent these obstacles, we have developed a new fabrication methodology that relies on dye encapsulation within liquid-filled capsules, thus enabling direct transfer of the luminescent properties from solution to the solid state and as such, rational design of miniaturized white-light-emitting materials. By introducing a thermally responsive chromophore into the capsules, these materials are further endowed with color tunability, which does not only allow ample modulation of the emitted color but also facilitate external fine control of the system so as to ensure precise realization of white light at the desired temperature and excitation wavelength.

Analysis of Exosome Transfer in Mammalian Cells by Fluorescence Recovery after Photobleaching

During the course of evolution, prokaryote and eukaryote cells have developed elegant and to some extent analogous strategies to communicate with each other and to adapt to their surrounding environment. Eukaryotic cells communicate with each other through direct interaction via juxtracrine signaling and/or by secreting soluble factors. These secreted factors can subsequently act on the cell itself (autocrine signaling) or interact with neighboring (paracrine signaling) and distant (endocrine signaling) cells. The transmission of signals between cells and tissues has been traditionally thought to be regulated by a protein-based signaling system. Typically, proteins destined for secretion into the extracellular milieu by exocytosis contain a canonical secretion-targeting sequence ( Théry et al., 2002 ). However, proteins with a non-continuous and stimulus-dependent secretion, proteins that do not contain a canonical secretion-targeting sequence, and species that might be too labile within the extracellular environment (DNA, mRNA, peptides, metabolites, miRNA and other RNA species), can be secreted in small membranous extracellular vesicles (EVs) in a specific manner ( Hagiwara et al., 2014 ). Exosomes represent one broad class of these secreted membrane vesicles with a diameter of 30-130 nm ( Cocucci et al., 2009 ; Théry et al., 2009 ; Kowal et al., 2014 ), which are formed inside the secreting cells in endosomal compartments called multivesicular bodies. Molecules loaded into exosomes as well as the intensity of the exosome transfer between cells are important parameters for the subsequent conditioning of recipient cells. Current knowledge on secretion of exosomes and their internalization in recipient cells remains incomplete. It is known that secretion intensity of exosomes varies according to the cellular type and its physiological state ( Garcia et al., 2016 ). Moreover, the different combination of transmembrane proteins on the surface of exosomes that facilitate the adhesion to the cell-extracellular matrix vary the avidity with which a recipient cell captures exosomes ( Hoshino et al., 2015 ). Here, we have developed an in vitro system by which the transfer of exosomes between cells in co-culture can be quantified using FRAP ('Fluorescence Recovery After Photobleaching') technology. This protocol has been used to analyze the effects of exosome transfer of hypoxia inducible factor 1-α (HIF-1α) in Mesenchymal Stem Cells (MSC; HIF-MSC) to Human Umbilical Cord Vein Endothelial Cells (HUVEC) (Gonzalez-King et al., 2017).

Analysis of the Hysteresis Behavior of Perovskite Solar Cells with Interfacial Fullerene Self-Assembled Monolayers

The use of self-assembled monolayers (SAMs) of fullerene derivatives reduces the hysteresis of perovskite solar cells (PSCs). We have investigated three different fullerene derivatives observing a decrease on hysteresis for all the cases. Several processes can contribute to the hysteresis behavior on PSCs. We have determined that the reduced hysteresis observed for devices with SAMs is produced by a decrease of the capacitive hysteresis. In addition, with an appropriated functionalization, SAMs can increase photocurrent even when no electron selective contact (ESC) is present and a SAM is deposited just on top of the transparent conductive oxide. Appropriated functionalization of the fullerene derivative, as introducing -CN groups, can enhance cell performance and reduce hysteresis. This work paves the way for a future enhancement of PSCs by a tailored design of the fullerene molecules that could actuate as an ESC by themselves.

Efficient passivated phthalocyanine-quantum dot solar cells

The power conversion efficiency of CdSe and CdS quantum dot sensitized solar cells is enhanced up to 45% for CdSe and 104% for CdS by passivation with an asymmetrically disulfide substituted phthalocyanine.

Effect of Organic and Inorganic Passivation in Quantum-Dot-Sensitized Solar Cells

The effect of semiconductor passivation on quantum-dot-sensitized solar cells (QDSCs) has been systematically characterized for CdS and CdS/ZnS. We have found that passivation strongly depends on the passivation agent, obtaining an enhancement of the solar cell efficiency for compounds containing amine and thiol groups and, in contrast, a decrease in performance for passivating agents with acid groups. Passivation can induce a change in the position of TiO2 conduction band and also in the recombination rate and nature, reflected in a change in the β parameter. Especially interesting is the finding that β, and consequently the fill factor can be increased with the passivation treatment. Applying this strategy, record cells of 4.65% efficiency for PbS-based QDSCs have been produced.

Heavy metals in the vicinity of a chlor-alkali factory in the Upper Negro River ecosystem, Northern Patagonia, Argentina

A study on heavy metal contents was performed in sediments and biota of the Upper Negro River (Alto Valle) aquatic system, Northern Patagonia, Argentina. The irrigation system of the Neuquén and Negro Rivers runs alongside these rivers for 150 km, supporting intensive agricultural and economical activities, mainly related to fruit production. A mercury cell chlor-alkali factory operated between 1951 and 1995. Close attention was given to the surroundings of the plant, located next to the Main Irrigation Channel, and to the PII drainage channel which received the plant's effluents between 1951 and 1979. From 1979 until its closure, the effluents were pumped above a ravine to a series of evaporation and decantation pools. Mercury and other heavy metals and metalloids (Ag, As, Ba, Co, Cr, Cs, Ni, Sb, Se, U and Zn) contents were measured for bottom sediments of the river and irrigation and drainage channels, for two widespread species of macrophytes (Potamogeton pectinatus and Myriophyllum brasiliensi), and for liver and muscle of native fish Odontesthes microlepidotus. River bed sediments show no evidence of heavy metal accumulation, however, biota might indicate that contaminants are entering the rivers. Mercury was the only element accumulated in the Main Irrigation channel sediments, the highest contents occurring in the surroundings of the nowadays shut-down chlor-alkali plant, returning to background values approximately 40 km downstream the plant. At the plant site, sediments from the center of the channel showed a decrease in Hg content in the upper 10 cm layer, ranging from 0.8 to 3.4 microg g(-1), and from 2.8 to 13.7 microg g(-1) in the next 10 cm lower layer. Conversely, the PII drainage channel sediments showed accumulation of Hg (2-4 microg g(-1)), distributed uniformly at different depths and along the channel, until its mouth at Negro river. Mercury contents of macrophytes downstream the chlor-alkali plant are higher than the baseline for the area, and macrophytes and fish liver from the PII drainage channel present the highest content in this element. The drainage channel system showed different degrees of impact, those channels flowing through densely populated areas being the most affected.

Atrioventricular septal defect: quantitative anatomy of the right ventricle

In 19 human fetal and newborn hearts with atrioventricular septal defect (AVSD), not associated with other anomalies, the two ventricles were studied morphometrically. A total of 17 different parameters were studied: nine in the right ventricle and eight in the left. In the right ventricle we analyzed ventricular wall thickness, length of right ventricular inflow and outflow tracts, and volume of right ventricular inflow and outflow tracts. The data for these parameters were compared with the patterns of normality published previously, and the volumetric data were compared with patterns of normality published previously by us. The ventricular inflow tract was shorter than the outflow tract, the difference being especially significant in the left ventricle. The length of the diaphragmatic wall of the heart in both the right and left ventricle was equal to the sum of the length of the inflow tract and the thickness of the ventricular wall at the apex.

Mutations affecting gluconate metabolism in Escherichia coli

A mutant of Escherichia coli K-12 that does not ferment gluconate on fermentation plates was isolated and characterized. This mutant, designated M2, shows a long lag for growth on gluconate mineral medium and somewhat reduced levels of high-affinity transport, gluconokinase, and gluconate-6-P dehydrase activities in the log phase of growth. The mutation involved is near malA. Deletion mutants in which malA region was affected were also studied. They were found to affect the function of different genes involved in gluconate metabolism.