Search results for "Kite"

Excitonic States in Semiconducting Two-dimensional Perovskites

2018

Hybrid organic/inorganic perovskites have emerged as efficient semiconductor materials for applications in photovoltaic solar cells with conversion efficiency above 20 \%. Recent experiments have synthesized ultra-thin two-dimensional (2D) organic perovskites with optical properties similar to those of 2D materials like monolayer MoS$_2$: large exciton binding energy and excitonic effects at room temperature. In addition, 2D perovskites are synthesized with a simple fabrication process with potential low-cost and large-scale manufacture. Up to now, state-of-the-art simulations of the excitonic states have been limited to the study of bulk organic perovskites. A large number of atoms in the …

Impedance analysis of perovskite solar cells: a case study

2019

Metal halide perovskites are mixed electronic-ionic semiconductors with an extraordinary rich optoelectronic behavior and the capability to function very efficiently as active layers in solar cells, with a record efficiency surpassing 23% nowadays. In this work, we carry out an impedance spectroscopy analysis of two perovskite solar cells with quite distinct optical and electrical characteristics, i.e. MAPbI3 and CsPbBr3-based devices. The main aim of the analysis is to establish how, regardless the inherent complexity of the impedance spectrum due to ionic effects, information like ideality factors, recombination losses and the collection efficiency can be qualitative and quantitatively as…

Crystalline-Size Dependence of Dual Emission Peak on Hybrid Organic Lead-Iodide Perovskite Films at Low Temperatures

2018

In this work, we have investigated the crystalline-size dependence of optical absorption and photoluminescence emission of CH3NH3PbI3 films, which is necessary to identify the potential practical applications of the gadgets based on perovskite films. This study was carried out at low temperatures to minimize the extra complexity induced by thermal effects. The purpose was to clarify the origin of the dual emission peak previously reported in the literature. We found that the grain size is responsible for the appearance or disappearance of this dual emission on CH3NH3PbI3 at low temperatures, whereas we have inferred that the thickness of the perovskite layer is a much more important factor …

Polystyrene nanoparticle-templated hollow titania nanosphere monolayers as ordered scaffolds

2018

We report a novel multi-step method for the preparation of ordered mesoporous titania scaffolds and show an illustrative example of their application to solar cells. The method is based on (monolayer) colloidal nanosphere lithography that makes use of polystyrene nanoparticles organised at a water–air interface and subsequently transferred onto a solid substrate. A titania precursor solution (titanium(IV) isopropoxide in ethanol) is then drop-cast onto the monolayer and left to “incubate” overnight. Surprisingly, instead of the expected inverse monolayer-structure, a subsequent calcination step of the precursor yields an ordered monolayer of hollow titania nanospheres with a wall thickness …

Proton Dynamics in In:BaZrO3: Insights on the Atomic and Electronic Structure from X-ray Absorption Spectroscopy

2009

The local structure of Ba2+, Zr4+, and In3+ in In:BaZrO3 is investigated with EXAFS for samples having 0 to 75% In3+ content. It is found that indium can be inserted in any ratio in the host matrix oxide and that the oxygen coordination shell displays an In-O distance very similar to the Zr-O length. In the Zr-rich compositions, there is a preferred dopant-vacancy association that, however, does not give rise to dopant-proton interaction in the hydrated samples. The tendency of Ba2+ to be attracted toward the dopant site is attributed to the electrostatic interaction with the dopant and to the structural rearrangement around the In3+ site. Third cumulant analysis at high temperatures (up to…

X-ray Spectroscopy of (Ba,Sr,La)(Fe,Zn,Y)O3-δIdentifies Structural and Electronic Features Favoring Proton Uptake

2020

Mixed protonic–electronic conducting oxides are key functional materials for protonic ceramic fuel cells. Here, (Ba,Sr,La)(Fe,Zn,Y)O3−δ perovskites are comprehensively investigated by X-ray spectroscopy (in oxidized and reduced states). Extended X-ray absorption fine structure shows that Zn,Y doping strongly increases the tendency for Fe–O–Fe buckling. X-ray absorption near-edge spectroscopy at the Fe K-edge and X-ray Raman scattering at the O K edge demonstrate that both iron and oxygen states are involved when the samples are oxidized, and for the Zn,Y doped materials, the hole transfer from iron to oxygen is less pronounced. This can be correlated with the observation that these material…

Non-Planar and Flexible Hole-Transporting Materials from Bis-Xanthene and Bis-Thioxanthene Units for Perovskite Solar Cells

2019

Two new hole-transporting materials (HTMs), BX-OMeTAD and BTX-OMeTAD, based on xanthene and thioxanthene units, respectively, and bearing p-methoxydiphenylamine peripheral groups, are presented for their use in perovskite solar cells (PSCs). The novelty of the newly designed molecules relies on the use of a single carbon-carbon bond ‘C−C’ as a linker between the two functionalized heterocycles, which increases the flexibility of the molecule compared with the more rigid structure of the widely used HTM spiro-OMeTAD. The new HTMs display a limited absorbance in the visible region, due to the lack of conjugation between the two molecular halves, and the chemical design used has a remarkably i…

TV:stä tuttu? : musiikkiterapia televisio-ohjelmissa Suomessa 1967-2007

2009

Linear Coassembly of Upconversion and Perovskite Nanoparticles: Sensitized Upconversion Emission of Perovskites by Lanthanide‐Doped Nanoparticles

2020

Sensitized emission of lead halide perovskite nanoparticles (LHPNPs) can be achieved by near‐infrared (NIR) excitation of nearby lanthanide‐doped upconversion nanoparticles (UCNPs) by using a low‐cost diode laser. Here, the first preparation of linear assemblies of core and core–shell NPs, as well as linear coassemblies of LHPNPs and UCNPs, within an open peapod‐like lead sulfate shell are reported. UCNPs with a NaYF4 matrix doped with ytterbium and thulium or erbium, and with an inert shell of NaYF4 in the case of core‐shell, and all‐inorganic CsPbX3 NPs (X = halide) are chosen for these studies. Interestingly, the lead sulfate shell enhances the luminescence of the core/core– shell UCNPs …

Y:BaZrO3 Perovskite Compounds I: DFT Study on the Unprotonated and Protonated Local Structures

2011

Y-doped BaZrO(3) derivatives were studied by density functional theory (DFT) to investigate the local arrangements of the octahedral sites in Pm3m cubic frameworks. Single- and double substitution of zirconium by yttrium were considered, including in the presence of a nearby oxygen vacancy. Although the structural symmetry of undoped barium zirconate was not modified after yttrium doping, the presence of yttrium induced several differences in the oxygen sites around it, according to the local geometrical arrangement of yttrium in the host matrix. As an example, the differences between such oxygen sites were shown in the presence of a proton. In this case, different stabilization energies ch…