I19-Small Molecule Single Crystal Diffraction
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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.
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Mar 2023
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I10-Beamline for Advanced Dichroism
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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.
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Mar 2023
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I07-Surface & interface diffraction
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Elena J.
Cassella
,
Emma L. K.
Spooner
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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.
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Feb 2023
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Elan D. R.
Mistry
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Daphné
Lubert-Perquel
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Irena
Nevjestic
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Giuseppe
Mallia
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Pilar
Ferrer
,
Kanak
Roy
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Georg
Held
,
Tian
Tian
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Nicholas M.
Harrison
,
Sandrine
Heutz
,
Camille
Petit
Diamond Proposal Number(s):
[26511]
Open Access
Abstract: A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered. Here, using an integrated experimental and first-principles-based computational approach, we demonstrate that paramagnetic isolated OB3 states are paramount to inducing prominent red-shifted light absorption. Conversely, we highlight the diamagnetic nature of O–B–O states, which are shown to cause undesired larger band gaps and impaired photochemistry. This study elucidates the importance of paramagnetism in BNO semiconductors and provides fundamental insight into its photophysics. The work herein paves the way for tailoring of its optoelectronic and photochemical properties for solar fuel synthesis.
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Feb 2023
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B18-Core EXAFS
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Yunpeng
Zuo
,
Nikolaos
Antonatos
,
Lukáš
Děkanovský
,
Jan
Luxa
,
Joshua D.
Elliott
,
Diego
Gianolio
,
Jiří
Šturala
,
Fabrizio
Guzzetta
,
Stefanos
Mourdikoudis
,
Jakub
Regner
,
Roman
Málek
,
Zdenek
Sofer
Diamond Proposal Number(s):
[31795]
Abstract: As a fascinating innovative class of effective catalysts
for hydrogen evolution reaction (HER), transition-metal tellurides
have emerged as attractive materials, but they are still suffering
from their intrinsic activity for practical applications. Defect
engineering constitutes a promising strategy to optimize the
electronic configuration of the catalyst and further improve the
HER activity. Herein, we present the successful fabrication of
PdTe2-based catalysts with three different types of vacancies (dPdTex), including single Pd, Te defect site, and double Te defect
sites, by using a two-step method. The obtained d-PdTex
demonstrated a remarkable HER activity with an overpotential of
76 mV at 10 mA cm−2 without iR compensation, which is far lower
than that of bulk PdTe2 (259 mV). The procedure followed in this
work may be extended to generate defect sites in a range of
different two-dimensional materials, thus further expanding their potential application fields.
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Feb 2023
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[25787, 27541, 29157]
Open Access
Abstract: Single-atom catalysts (SACs) on hematite photoanodes are efficient cocatalysts to boost photoelectrochemical performance. They feature high atom utilization, remarkable activity, and distinct active sites. However, the specific role of SACs on hematite photoanodes is not fully understood yet: Do SACs behave as a catalytic site or as a spectator? By combining spectroscopic experiments and computer simulations, we demonstrate that single-atom iridium (sIr) catalysts on hematite (α-Fe2O3/sIr) photoanodes act as a true catalyst by trapping holes from hematite and providing active sites for the water oxidation reaction. In situ transient absorption spectroscopy showed a reduced number of holes and shortened hole lifetime in the presence of sIr. This was particularly evident on the second timescale, indicative of fast hole transfer and depletion toward water oxidation. Intensity-modulated photocurrent spectroscopy evidenced a faster hole transfer at the α-Fe2O3/sIr/electrolyte interface compared to that at bare α-Fe2O3. Density functional theory calculations revealed the mechanism for water oxidation using sIr as a catalytic center to be the preferred pathway as it displayed a lower onset potential than the Fe sites. X-ray photoelectron spectroscopy demonstrated that sIr introduced a mid-gap of 4d state, key to the fast hole transfer and hole depletion. These combined results provide new insights into the processes controlling solar water oxidation and the role of SACs in enhancing the catalytic performance of semiconductors in photo-assisted reactions.
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Jan 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[29757]
Open Access
Abstract: Aqueous phase reforming (APR) of waste oxygenates offers the potential for sustainable hydrogen production. However, catalyst stability remains elusive, due to the aggressive hydrothermal conditions employed. Herein, we show that the catalytic performance and stability of Pt supported on LaAlO3 catalysts for glycerol APR is strongly influenced by the phase purity of LaAlO3. Calcination of the support at 700 °C produces the LaAlO3 perovskite phase and an amorphous lanthanum carbonate phase, which can be removed by calcination at higher temperature. Catalysts comprised of phase pure LaAlO3 were notably more active, with a support calcination temperature of 1100 °C resulting in 20.4% glycerol conversion (TOF 686 h−1) in a 2 h batch reaction. Interestingly, all the catalysts, regardless of LaAlO3 phase purity, eventually transform into Pt/LaCO3OH-AlO(OH) during reaction, but only in the presence of evolved carbon dioxide, itself produced from glycerol reforming. Studies using simulated reaction products showed that organic acid products (lactic acid), in the absence of CO2, facilitated La leaching and loss of crystallinity. A carbonate source (CO2) is essential to limit La leaching and form stable Pt/LaCO3OH. Pt supported on LaCO3OH and AlO(OH) are stable and active catalysts during APR reactions. Yet, the rate of perovskite phase decomposition strongly influences the final catalyst performance, with the initially phase impure LaAlO3 decomposing too quickly to facilitate Pt redistribution. LaAlO3 calcined at higher temperatures evolved more slowly and consequently produced more active catalysts.
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Dec 2022
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B18-Core EXAFS
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Maria
Retuerto
,
Laura
Pascual
,
Jorge
Torrero
,
Mohamed Abdel
Salam
,
Alvaro
Tolosana-Moranchel
,
Diego
Gianolio
,
Pilar
Ferrer
,
Paula
Kayser
,
Vincent
Wilke
,
Svenja
Stiber
,
Veronica
Celorrio
,
Mohamed
Mokthar
,
Daniel García
Sanchez
,
Aldo Saul
Gago
,
Kaspar Andreas
Friedrich
,
Miguel Antonio
Peña
,
José Antonio
Alonso
,
Sergio
Rojas
Diamond Proposal Number(s):
[27733]
Open Access
Abstract: Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr2CaIrO6 achieves 10 mA cm−2 at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO6 octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr2CaIrO6 as anode and low Ir loading (0.4 mgIr cm−2). The cell achieves 2.40 V at 6 A cm−2 (overload) and no loss in performance at a constant 2 A cm−2 (nominal load). Thus, reducing Ir use without compromising efficiency and lifetime.
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Dec 2022
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[26730]
Open Access
Abstract: Hydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers of <10−7 was ∼50% of the pore volume and independent of the pore fluid pressure. Hydrogen recovery during secondary imbibition at a capillary number of 2.4 × 10−6 systematically decreased with pressure, with 80%, 78% and 57% of the initial hydrogen recovered at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4 × 10−6 increased hydrogen recovery. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media.
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Nov 2022
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I07-Surface & interface diffraction
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Margherita
Taddei
,
Joel A.
Smith
,
Benjamin M.
Gallant
,
Suer
Zhou
,
Robert J. E.
Westbrook
,
Yangwei
Shi
,
Jian
Wang
,
James N.
Drysdale
,
Declan P.
Mccarthy
,
Stephen
Barlow
,
Seth R.
Marder
,
Henry J.
Snaith
,
David S.
Ginger
Diamond Proposal Number(s):
[30612]
Abstract: We show that adding ethylenediamine (EDA) to perovskite precursor solutions improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1–xCsxPb(I1–yBry)3, which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol % EDA, we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V and a champion maximum-power-point-tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA+ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties.
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Nov 2022
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