1,721,042 research outputs found
Synergies and compromises between charge and energy transfers in three-component organic solar cells
Full text linkIn this paper, we developed different three-component organic heterojunction structures supported by PET/ITO substrates with the aim to study the possible synergies and/or compromises between charge transfer (CT) and energy transfer (ET) processes in organic solar cells (OSCs). As components, we employed poly(3-hexylthiophene-2,5-diyl) (P3HT; donor), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM; acceptor) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) that is known to give good ET to P3HT. At first, we observed that in a planar heterojunction (PHJ) solar cell, F8BT has to be properly located in between P3HT and PCBM to get a cascade energy level configuration allowing for a better CT and power conversion efficiency. Then, we observed that by producing a P3HT:F8BT blend, the energy transfer process can be improved in the P3HT:F8BT/PCBM active layer. This may enable decreasing the thickness of the active layer while maintaining a similar PCE that is very interesting for the development of transparent OSCs. However, the P3HT:F8BT blend limits the P3HT-PCBM CT with respect to a P3HT/F8BT/PCBM PHJ, showing that a compromise between CT and ET is needed to get a higher PCE or higher transparency. By the above approach, in this paper, we developed highly transparent heterojunction structures for solar cell devices with PCEs comparable to those observed from the colorful reference P3HT/PCBM PHJ solar cells on PET/ITO substrates
Bismuth drives the morphology and piezoresistivity of lead-free (TMSO)3Sn3xBi2(1−x)I9 halide perovskite thin films
Full text linkThe design of lead-free perovskite thin films with tunable optoelectronic properties is a hot topic in materials science, since it might enable the discovery of interesting properties outside the extensively explored field of photovoltaic solar cells. Herein, we report on the bending strain sensitivity of a lead-free hybrid organic–inorganic monodimensional iodide (TMSO)3Sn3xBi2(1−x)I9 (0 ≤ x ≤ 1) showing complete miscibility of Bi3+ and Sn2+, with TMSO being trimethylsulfoxonium. As previously shown in monodimensional haloplumbates, vacant cation sites are formed upon Bi3+ insertion, which in turn lead to the tunable shrinkage of the unit cell along the a axis. The effective substitution of Bi3+ and Sn2+ and their chemical state are investigated with EXAFS/XANES. Notably, Bi3+ also lowers the bandgap from 2.75 eV to 1.96 eV. Thin films prepared by spin coating on flexible ITO/PET supports are then used to assess the bending strain sensitivity as a function of composition, reaching an optimal value of the gauge factor (about 110 at 0.6% strain) at the highest Bi3+ concentration. The observed features are explained in terms of the surface morphology of the films as probed by AFM, highlighting the role of Bi3+. The effects on microstructural and electrical features after strain are further investigated by SEM and EIS, underpinning the key role of microcracks and delamination for triggering the observed responsivity to bending strain
Boosting the Performance of One-Step Solution-Processed Perovskite Solar Cells Using a Natural Monoterpene Alcohol as a Green Solvent Additive
Full text linkThe perovskite film is the core of a perovskite solar cell (PSC), and its quality is crucial for the performance of such devices. The morphology, crystallinity, and surface coverage of the perovskite layer greatly affect the power conversion efficiency (PCE), hysteresis, and long-term stability of PSCs. The incorporation of appropriate solvent additives in the perovskite precursor solution is an effective strategy to control the film morphology and reduce the defects and grain boundaries. However, the commonly used solvent additives are environmentally harmful and highly toxic. In this work, α-terpineol (a nontoxic, eco-friendly, and low-cost monoterpene alcohol) is employed for the first time as an alternative green solvent additive to improve the quality of one-step solution-processed CH3NH3PbI3–xClx films and to restrain nonradiative recombination in the corresponding devices. An in-depth investigation of the physicochemical effects induced by such a high-boiling-point, polar protic solvent when incorporated into a conventional perovskite solvent system is provided. The collected data demonstrate that the addition of a precise amount of α-terpineol can generate uniform and highly crystalline perovskite films with improved photovoltaic performances. Through this approach, the PCE of planar n–i–p PSCs is boosted up to 17.5% (against 16.1% of the top control device) with reduced hysteresis and enhanced ambient stability
MORPHOLOGY AND PIEZORESISTIVITY OF LEAD-FREE (TMSO)3Sn3xBi2(1-x)I9 HALIDE PEROVSKITE THIN FILMS INFLUENCED BY BISMUTH
Full text linkThe development of lead-free perovskite thin films with adjustable optoelectronic properties is a
highly discussed topic in materials science. In this study, we present the bending strain sensitivity
of a lead-free hybrid organic-inorganic monodimensional iodide (TMSO)3Sn3xBi2(1-x)I9 (0 ≤ x ≤
1), with TMSO representing trimethylsulfoxonium. As previously observed in monodimensional
haloplumbates, the insertion of Bi3+ results in the formation of vacant cation sites, which in turn
leads to the adjustable shrinkage of the unit cell along the a lattice axis.[1-3] Thin films, prepared
by spin coating on flexible ITO/PET supports, are then employed to assess the bending strain
sensitivity as a function of composition. The films produced with low amount or without Bi3+
show similar or worse piezoresistive properties than the ITO control, whereas when Bi3+ is the
predominant metal ion, the corresponding piezoresistive features are enhanced (Fig. 1). An
optimal composition is found in 75 % Bi, where the bandgap can be lowered down to 1.96 eV,
and the gauge factor improves by increasing the bending strain, up to 110 at 0.6% strains.[4] The
films were analyzed by AFM to explain the observed features in terms of surface morphology.
The microstructural and electrical properties after deformation were explored by SEM and EIS.
This study represents an initial step in designing a lead-free halide perovskite with unique
piezoresistive properties for bending sensors requiring sensitivity to small and high bending
angles, applicable in soft robotics and wearable electronics
Preparation and structural studies on the tBu2Sn(IV) complexes with aromatic mono- and dicarboxylic acids containing hetero {N} donor atom
No full textNine complexes of 'Bu2Sn(IV)(2+) were obtained in the solid state with ligands containing -COOH group(s) and aromatic (N) donor atom. The binding sites of the ligands were identified by FT-IR spectroscopic measurements. It was found that in most cases the -COO- groups are co-ordinated in monodentate manner. Nevertheless, in some of our complexes, the -COO- group forms bridges between two central {Sn} atoms resulting in the formation of an oligomeric structure, a motif that is characteristic only to the nicotinate compound. These pieces of information and the rationalisation of the experimental Sn-119 Mossbauer nuclear quadrupole splittings, Delta, - according to the point charge model formalism - support the formation of octahedral (O-h) or trigonal bipyramidal (TBP) molecular structures. The X-ray diffraction analysis of one complex obtained as single crystal revealed the distortion of the TBP geometry towards square pyramidal (SP) one. This was rationalised by PM3 molecular modelling of the 'Bu2Sn(pdc) complex. In the asymmetric unit, the two chemically similar but symmetry independent molecules form pseudo-dimers, in which the Sn...Sn separation amounts to ca. 6.4 Angstrom. The crystal lattice is stabilised by C-H... O hydrogen bonding between individual molecules. (C) 2004 Elsevier B.V. All rights reserved
Blue-light-driven photoactivity of L-cysteine-modified graphene quantum dots and their antibacterial effects
No full textThe widespread abuse of traditional antibiotics has led to a global rise in antibiotic-resistant bacteria, which give in return unprecedented health risks. Therefore, there is a large and urgent need for the development of new, smart antibacterial agents able to efficiently kill or inhibit bacterial growth. In this study, we investigated the antibacterial activity of S, N-doped Graphene Quantum Dots (GQDs) as a light-triggered antibacterial agent. Gamma irradiation was employed as a tool to achieve one-step modification of GQDs in the presence of L-cysteine amino acid as a source of heteroatoms. X-ray Photoelectron Spectroscopy (XPS), nuclear magnetic
resonance (NMR), and zeta potential measurements provided the necessary data to clarify the structure of modified dots and verify the introduction of both S- and N-atoms in GQDs structure, but also severe changes in the aromatic, sp2 domains. Namely, γ-irradiation caused a bonding of S atoms in 1.14 at.% mainly as thiol groups, and N in 1.81 at.% as amino groups, but sp2 contribution in GQD structure was lowered from 63.00 to 4.86 at.%, as measured in dots irradiated at a dose of 200 kGy. Fluorescence quenching measurements showed that L-cysteine-modified dots are able to bind to human serum albumin. The antibacterial activity of GQDs
combined with 1 and 6 h of blue light (470 nm) irradiation was tested against 8 bacterial strains. GQD-cys-25 sample provided the best results, with minimum inhibitory concentration (MIC) as low as 125 μg/mL against S. aureus, E. faecalis, and E. coli after only 1 h of blue light exposure
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
