B18-Core EXAFS
|
Open Access
Abstract: New and exotic ground states of magnetic materials are highly sought after and are extensively studied for the insights they provide into the thermodynamics of disorder and fundamental magnetic interactions. By controlling the crystal structure of an appropriate magnetic lattice, it is possible to cause the strong magnetic exchange interactions to sum to zero and so be frustrated. Due to the presence of this frustration, the lowest energy configuration that results may be crucially dependent on the tiniest of energy differences between a multitude of states that have (almost) the same energy. The keen interest in these materials arises from the fact that these finely balanced systems offer a way of probing classical or quantum mechanical interactions that are of fundamental importance but are too weak to be observed in non-frustrated systems. Here, we combine local and crystallographic probes of the cation-ordered double perovskite Ba2MnMoO6 that contains a face-centered cubic lattice of S = 5/2 Mn2+ cations. Neutron diffraction measurements below 9.27(7) K indicate that a fourfold degenerate non-collinear antiferromagnetic state exists with almost complete ordering of the Mn2+ spins. Muon spin relaxation measurements provide a local probe of the magnetic fields inside this material over the t1/2 = 2.2 µs lifetime of a muon, indicating a slightly lower Néel transition temperature of 7.9(1) K. The dc susceptibility data do not show the loss of magnetization that should accompany the onset of the antiferromagnetic order; they indicate that a strongly antiferromagnetically coupled paramagnetic state [θ = −73(3) K] persists down to 4 K, at which temperature a weak transition occurs. The behavior of this material differs considerably from the closely related compositions Ba2MnMO6 (M = W, Te), which show collinear ordering arrangements and well defined antiferromagnetic transitions in the bulk susceptibility. This suggests that the Mo6+ cation leads to a fine balance between the nearest and next-nearest neighbor superexchange in these frustrated double perovskite structures.
|
May 2023
|
|
I14-Hard X-ray Nanoprobe
|
Diamond Proposal Number(s):
[20420, 28521]
Open Access
Abstract: All-perovskite tandem solar cells beckon as lower cost alternatives to conventional single-junction cells. Solution processing has enabled rapid optimization of perovskite solar technologies, but new deposition routes will enable modularity and scalability, facilitating technology adoption. Here, we utilize 4-source vacuum deposition to deposit FA0.7Cs0.3Pb(IxBr1–x)3 perovskite, where the bandgap is changed through fine control over the halide content. We show how using MeO-2PACz as a hole-transporting material and passivating the perovskite with ethylenediammonium diiodide reduces nonradiative losses, resulting in efficiencies of 17.8% in solar cells based on vacuum-deposited perovskites with a bandgap of 1.76 eV. By similarly passivating a narrow-bandgap FA0.75Cs0.25Pb0.5Sn0.5I3 perovskite and combining it with a subcell of evaporated FA0.7Cs0.3Pb(I0.64Br0.36)3, we report a 2-terminal all-perovskite tandem solar cell with champion open circuit voltage and efficiency of 2.06 V and 24.1%, respectively. This dry deposition method enables high reproducibility, opening avenues for modular, scalable multijunction devices even in complex architectures.
|
May 2023
|
|
B18-Core EXAFS
|
Open Access
Abstract: The Fischer–Tropsch (FT) synthesis is traditionally associated with fossil fuel consumption, but recently this technology has emerged as a keystone that enables the conversion of captured CO2 with sustainable hydrogen to energy-dense fuels and chemicals for sectors which are challenging to be electrified. Iron-based FT catalysts are promoted with alkali and transition metals to improve reducibility, activity, and selectivity. Due to their low concentration and the metastable state under reaction conditions, the exact speciation and location of these promoters remain poorly understood. We now show that the selectivity promoters such as potassium and manganese, locked into an oxidic matrix doubling as a catalyst support, surpass conventional promoting effects. La1–xKxAl1–yMnyO3−δ (x = 0 or 0.1; y = 0, 0.2, 0.6, or 1) perovskite supports yield a 60% increase in CO conversion comparable to conventional promotion but show reduced CO2 and overall C1 selectivity. The presented approach to promotion seems to decouple the enhancement of the FT and the water–gas shift reaction. We introduce a general catalyst design principle that can be extended to other key catalytic processes relying on alkali and transition metal promotion.
|
May 2023
|
|
I11-High Resolution Powder Diffraction
|
Aleksandra
Mielewczyk-Gryń
,
Shuhao
Yang
,
Maria
Balaguer
,
Ragnar
Strandbakke
,
Magnus H.
Sørby
,
Iga
Szpunar
,
Agnieszka
Witkowska
,
Sebastian
Wachowski
,
Jose M.
Serra
,
Alexandra
Navrotsky
,
Maria
Gazda
Abstract: This study concerns energetics of formation and the stability in high water partial pressure of BaLnCo2O6−δ, (Ln = La, Pr, Nd, and Gd) (BLnC) and BaGd1−xLaxCo2O6−δ, where x = 0.2, 0.5, and 0.7 (BGLC) double perovskite cobaltites. Those materials are extensively studied due to their potential applications as a positrode in electrochemical devices. Therefore, their stability under such conditions is a key issue. All investigated materials are thermodynamically stable relative to binary oxides and exhibit strongly exothermic enthalpies of formation. Moreover, BaGd0.3La0.7Co2O6−δ and BaGd0.8La0.2Co2O6−δ remain the main perovskite structure up to 3 bars of water vapor at 400 °C. At higher steam pressure, reaching 10 bar at 300 °C, the partial decomposition to constituent oxides and hydroxides was observed. The BGLC compounds exhibit higher negative formation enthalpies in comparison to single-Ln compositions, which does not translate into higher chemical stability under high steam pressures since the BLnC series retained the main perovskite structure at higher temperatures as well as in higher water vapor pressures.
|
Apr 2023
|
|
B18-Core EXAFS
|
Madeleine
Han
,
Isabel
Gómez-Recio
,
Daniel Gutiérrez
Martín
,
Nathaly
Ortiz Peña
,
Maria Luisa
Ruiz-González
,
Mohamed
Selmane
,
José M.
González-Calbet
,
Ovidiu
Ersen
,
Andrea
Zitolo
,
Benedikt-Kaiser
Lassalle
,
David
Portehault
,
Christel
Laberty-Robert
Diamond Proposal Number(s):
[21747]
Abstract: Manganese and cobalt perovskite oxides are among the most active precious metal-free electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), respectively. Herein, we question the role of the cationic composition and charge state in manganite, cobaltite, and mixed Mn/Co perovskites in the mechanism of oxygen electrocatalysis for ORR and OER. We synthesize in molten salts a range of perovskite nanoparticles active in ORR (single B-site (LaMn)1−γO3 and (La0.7Sr0.3Mn)1−γO3), in OER (single B-site La0.67Sr0.33CoO3−δ), and in both ORR and OER (mixed B-site (LaMn0.6Co0.4)1−γO3). By using operando X-ray absorption spectroscopy coupled to ex situ electron energy loss spectroscopy, we show that Mn and Co in single B-site perovskites undergo changes in oxidation states at the steady state during electrocatalysis, while their oxidation states remain unchanged in the mixed Mn/Co perovskite during OER and ORR. We relate these distinct behaviors to modifications of the rate-determining steps of both the OER and ORR electrocatalytic cycles, triggered by an increased covalency of B–O bonds in the mixed perovskites. These results highlight how simple cationic substitutions, accompanied by a control of cationic vacancies, offer a pathway to tune oxygen electrocatalysis.
|
Apr 2023
|
|
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[18786]
Open Access
Abstract: The crystallization of a new series of A-site substituted lanthanum ferrite materials (La1–xREx)FeO3 was explored by the hydrothermal method at 240 °C, for rare earth (RE) = Nd, Sm, Gd, Ho, Er, Yb, and Y, with 0 ≤ x ≤ 1. The effect of elemental substitution on the morphological, structural, and magnetic properties of the materials was studied using high-resolution powder X-ray diffraction, energy dispersive spectroscopy (EDS) on the scanning electron microscope, Raman spectroscopy, and SQUID magnetometry. If the radius of the La3+ and the substituent ions is similar, such as for Nd3+, Sm3+, and Gd3+, homogeneous solid solutions are formed, with the orthorhombic GdFeO3-type structure, and a continuous evolution of Raman spectra with composition and distinct magnetic behavior from the end members. When the radius difference between substituents and La3+ is large, such as for Ho3+, Er3+, Yb3+, and Y3+, then instead of forming solid solutions, crystallization in separate phases is found. However, low levels of element mixing are found and intergrowths of segregated regions give composite particles. In this case, the Raman spectra and magnetic behavior are characteristic of mixtures of phases, while EDS shows distinctive elemental segregation. A-site replacement induces an evolution in the crystallite shape with an increasing amount of substituent ions and this is most evident for RE = Y from cube-shaped crystals seen for LaFeO3 to multipodal crystals for (La1–xYx)FeO3, providing evidence for a phase-separation-driven evolution of morphology.
|
Mar 2023
|
|
I19-Small Molecule Single Crystal Diffraction
|
Diamond Proposal Number(s):
[22240]
Open Access
Abstract: Hole transport materials (HTMs) based on truxene cores have emerged as promising candidates in recent years. They are noted by properties such as higher hole mobility and higher glass transition temperature than the 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenamine)-9,9′-spirobiflourene (spiro-MeOTAD), as well as good hydrophobicity and energy alignment. Truxene derivatives have been studied for application in transistors, OLEDs, lasers, supercapacitors, etc., however, there are only a few studies on their use as HTMs in perovskite solar cells (PSCs). In this study, we synthesised a novel small organic molecule HTM with a monothiatruxene (TrxS) core, namely TrxS-2MeOTAD, and characterised its basic properties and ability as an HTM in n–i–p planar PSCs. The TrxS-2MeOTAD showed suitable electrochemical, optical, structural and thermal properties for an HTM, such as a relatively high glass transition temperature (145 °C) and stable amorphous nature when deposited as films. The PSCs using TrxS-2MeOTAD achieved 18.9% power conversion efficiency (PCE) compared to the reference spiro-MeOTAD at 19.3% PCE. The unencapsulated TrxS-2MeOTAD devices showed better operational stability than spiro-MeOTAD, with a 1.5 times longer lifetime under constant AM1.5G illumination. Our results suggest that small molecules based on the TrxS core can be a promising direction for the development of alternative HTMs.
|
Mar 2023
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[16141]
Open Access
Abstract: Owing to the unique chemical and electronic properties arising from 3d-electrons, substitution with transition metal ions is one of the key routes for engineering new functionalities into materials. While this approach has been used extensively in complex metal oxide perovskites, metal halide perovskites have largely resisted facile isovalent substitution. In this work, it is demonstrated that the substitution of Co2+ into the lattice of methylammonium lead triiodide imparts magnetic behavior to the material while maintaining photovoltaic performance at low concentrations. In addition to comprehensively characterizing its magnetic properties, the Co2+ ions themselves are utilized as probes to sense the local electronic environment of Pb in the perovskite, thereby revealing the nature of their incorporation into the material. A comprehensive understanding of the effect of transition metal incorporation is provided, thereby opening the substitution gateway for developing novel functional perovskite materials and devices for future technologies.
|
Mar 2023
|
|
I07-Surface & interface diffraction
|
Yuqi
Sun
,
Lishuang
Ge
,
Linjie
Dai
,
Changsoon
Cho
,
Jordi
Ferrer Orri
,
Kangyu
Ji
,
Szymon J.
Zelewski
,
Yun
Liu
,
Alessandro J.
Mirabelli
,
Youcheng
Zhang
,
Jun-Yu
Huang
,
Yusong
Wang
,
Ke
Gong
,
May Ching
Lai
,
Lu
Zhang
,
Dan
Yang
,
Jiudong
Lin
,
Elizabeth M.
Tennyson
,
Caterina
Ducati
,
Samuel D.
Stranks
,
Lin-Song
Cui
,
Neil C.
Greenham
Diamond Proposal Number(s):
[30575]
Abstract: Perovskite light-emitting diodes (LEDs) have attracted broad attention due to their rapidly increasing external quantum efficiencies (EQEs)1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. However, most high EQEs of perovskite LEDs are reported at low current densities (<1 mA cm−2) and low brightness. Decrease in efficiency and rapid degradation at high brightness inhibit their practical applications. Here, we demonstrate perovskite LEDs with exceptional performance at high brightness, achieved by the introduction of a multifunctional molecule that simultaneously removes non-radiative regions in the perovskite films and suppresses luminescence quenching of perovskites at the interface with charge-transport layers. The resulting LEDs emit near-infrared light at 800 nm, show a peak EQE of 23.8% at 33 mA cm−2 and retain EQEs more than 10% at high current densities of up to 1,000 mA cm−2. In pulsed operation, they retain EQE of 16% at an ultrahigh current density of 4,000 mA cm−2, along with a high radiance of more than 3,200 W s−1 m−2. Notably, an operational half-lifetime of 32 h at an initial radiance of 107 W s−1 m−2 has been achieved, representing the best stability for perovskite LEDs having EQEs exceeding 20% at high brightness levels. The demonstration of efficient and stable perovskite LEDs at high brightness is an important step towards commercialization and opens up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers.
|
Mar 2023
|
|
I07-Surface & interface diffraction
|
Elena J.
Cassella
,
Emma L. K.
Spooner
,
Joel A.
Smith
,
Timothy
Thornber
,
Mary E.
O'Kane
,
Robert D. J.
Oliver
,
Thomas E.
Catley
,
Saqlain
Choudhary
,
Christopher J.
Wood
,
Deborah B.
Hammond
,
Henry J.
Snaith
,
David G.
Lidzey
Diamond Proposal Number(s):
[30612]
Open Access
Abstract: High temperature post-deposition annealing of hybrid lead halide perovskite thin films—typically lasting at least 10 min—dramatically limits the maximum roll-to-roll coating speed, which determines solar module manufacturing costs. While several approaches for “annealing-free” perovskite solar cells (PSCs) have been demonstrated, many are of limited feasibility for scalable fabrication. Here, this work has solvent-engineered a high vapor pressure solvent mixture of 2-methoxy ethanol and tetrahydrofuran to deposit highly crystalline perovskite thin-films at room temperature using gas-quenching to remove the volatile solvents. Using this approach, this work demonstrates p-i-n devices with an annealing-free MAPbI3 perovskite layer achieving stabilized power conversion efficiencies (PCEs) of up to 18.0%, compared to 18.4% for devices containing an annealed perovskite layer. This work then explores the deposition of self-assembled molecules as the hole-transporting layer without annealing. This work finally combines the methods to create fully annealing-free devices having stabilized PCEs of up to 17.1%. This represents the state-of-the-art for annealing-free fabrication of PSCs with a process fully compatible with roll-to-roll manufacture.
|
Feb 2023
|
|
