I07-Surface & interface diffraction
I09-Surface and Interface Structural Analysis
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Alessandro J.
Mirabelli
,
Birgit
Kammlander
,
Yang
Lu
,
Rahul Mahavir
Varma
,
Qichun
Gu
,
Karen
Radetzky
,
Thomas A.
Selby
,
Tianjun
Liu
,
Stefania
Riva
,
Zimu
Wei
,
Tien-Lin
Lee
,
Jonathan
Rawle
,
Hakan
Rensmo
,
Miguel
Anaya
,
Ute B.
Cappel
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[30043, 32266, 30838, 33096]
Open Access
Abstract: To commercialize lead halide perovskites as light-emitting diodes (LEDs), the operational device lifetime needs to be drastically improved. For this to be achieved, an understanding of degradation behavior under bias is crucial. Herein, we perform operando measurements of the structural, chemical, and electronic changes using synchrotron-based grazing-incidence wide-angle X-ray scattering and hard X-ray photoelectron spectroscopy on full-stack deep blue mixed bromide/chloride lead halide perovskite LEDs. While a clear drop in optoelectronic performance is recorded under electrical bias, the accompanying X-ray scattering data reveals only minor changes in structural properties. However, photoelectron spectroscopy reveals substantial chemical changes at the electron-injecting interface after bias is applied, including the formation of unwanted metallic lead and a new chlorine species that is not in the perovskite structure. These operando approaches give important structural and interfacial perspectives to reveal the degradation mechanisms in these LEDs and highlight the need to address the top electron-injecting interface to realize step-changes in operational stability.
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Jun 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
I09-Surface and Interface Structural Analysis
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Nickil
Shah
,
Galo J.
Paez Fajardo
,
Hrishit
Banerjee
,
Gaurav C.
Pandey
,
Ashok S.
Menon
,
Muhammad
Ans
,
Veronika
Majherova
,
Gerard
Bree
,
Satish
Bolloju
,
David .
Grinter
,
Pilar
Ferrer
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Melanie
Loveridge
,
Andrew J.
Morris
,
Clare P.
Grey
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[30201, 33459]
Open Access
Abstract: In Ni-rich layered oxide cathodes, cycling above the oxygen-loss threshold voltage (∼4.3 V vs Li+/Li) promotes structural transformations at the cathode surface. These transformations can result in various thermodynamically favorable rocksalt-like (RSL) structures (NiO, NiOx, and/or LiyNizO) that have different Li+ transport properties. Elucidating the precise phase type in the RSL can help determine design strategies to improve Li+ kinetics and identify design rules to suppress capacity fade in Ni-rich cathodes. This study utilizes surface-sensitive X-ray absorption spectroscopy in combination with first-principles simulations and distinguishes the layered oxide spectroscopic features from those of surface-reduced layers of pure NiO and LixNi1–xO. The transport of lithium ions through this oxygen-loss-induced surface-reconstructed layer is studied with operando X-ray diffraction in a pouch cell as a function of cycling aging and constant voltage protocols.
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Feb 2025
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E02-JEM ARM 300CF
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Sangcheol
Yoon
,
Braulio
Reyes-Suárez
,
Sang T.
Pham
,
Hervé
Vezin
,
Yeny A.
Tobon
,
Myeongjae
Lee
,
Sam
Mugiraneza
,
Brian Minki
Kim
,
Mariane Yuka Tsubaki
Oide
,
Seongju
Yoo
,
Seunggu
Lee
,
Shu Hui
Wang
,
Sean M.
Collins
,
Christopher M.
Bates
,
Yongsup
Park
,
Bongsoo
Kim
,
G. N. Manjunatha
Reddy
,
Thuc-Quyen
Nguyen
Diamond Proposal Number(s):
[34607]
Abstract: Understanding efficiency–durability relationships and related mitigation strategies is an important step toward the commercialization of organic photovoltaics (OPVs). Here, we report that a photoactivated 6-bridged azide cross-linker (6Bx) improves the morphological stability by suppressing the thermally activated diffusion of (Y6) acceptor molecules in PM6:Y6 bulk-heterojunction (BHJ)-based OPVs. Cross-linked PM6:Y6 (0.05 wt % 6Bx) BHJ OPVs retain 93.4% of the initial power conversion efficiency upon thermal aging at 85 °C for 1680 h (T80 = 3290 h). Molecular origins of enhanced thermal stability are corroborated by optical spectroscopy, surface imaging, 2D solid-state nuclear magnetic resonance (ssNMR), Raman spectroscopy, scanning electron diffraction (SED) measurements, and analysis of the BHJ thin films. The facile single-step cross-linking strategy in conjugation with advanced characterization methods presented in the study paves the way toward developing durable OPVs based on non-fullerene acceptors (NFAs).
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Dec 2024
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B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Matthew
Ogley
,
Ashok S.
Menon
,
Beth J.
Johnston
,
Gaurav
Pandey
,
Innes
Mcclelland
,
Xiaoqun
Shi
,
Stefano
Agrestini
,
Veronica
Celorrio
,
Gabriel E.
Perez
,
Samuel G.
Booth
,
Jordi
Cabana
,
Serena A.
Cussen
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33292, 33173]
Open Access
Abstract: In layered lithium transition metal oxide cathodes, high-voltage operation is accompanied by the formation of oxygen dimers, which are widely used as an indicator of oxygen-redox activity. However, understanding the role that oxygen dimerization plays in facilitating charge compensation is still needed. Li2NiO3 (a 3d8L2-containing compound, where L is a ligand hole) is studied as a model system, where oxygen dimerization is shown to occur without cathode oxidation. Electrochemical cycling results in a net reduction of the cathode, accompanied by structural transformations, despite spectroscopic features of oxygen dimers arising at the top-of-charge. Here, oxygen dimerization is shown to coexist alongside a structurally transformed and electronically reduced cathode structure, thus highlighting that O dimerization is independent of bulk redox processes. This makes it clear that a thermodynamically derived transformation toward a reduced phase remains the only variable capable of generating O–O dimers in Li2NiO3.
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Aug 2024
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I13-1-Coherence
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Kieran W. P.
Orr
,
Jiecheng
Diao
,
Krishanu
Dey
,
Madsar
Hameed
,
Milos
Dubajic
,
Hayley L.
Gilbert
,
Thomas A.
Selby
,
Szymon J.
Zelewski
,
Yutong
Han
,
Melissa R.
Fitzsimmons
,
Bart
Roose
,
Peng
Li
,
Jiadong
Fan
,
Huaidong
Jiang
,
Joe
Briscoe
,
Ian K.
Robinson
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[31362]
Open Access
Abstract: Strain is an important property in halide perovskite semiconductors used for optoelectronic applications because of its ability to influence device efficiency and stability. However, descriptions of strain in these materials are generally limited to bulk averages of bare films, which miss important property-determining heterogeneities that occur on the nanoscale and at interfaces in multilayer device stacks. Here, we present three-dimensional nanoscale strain mapping using Bragg coherent diffraction imaging of individual grains in Cs0.1FA0.9Pb(I0.95Br0.05)3 and Cs0.15FA0.85SnI3 (FA = formamidinium) halide perovskite absorbers buried in full solar cell devices. We discover large local strains and striking intragrain and grain-to-grain strain heterogeneity, identifying distinct islands of tensile and compressive strain inside grains. Additionally, we directly image dislocations with surprising regularity in Cs0.15FA0.85SnI3 grains and find evidence for dislocation-induced antiphase boundary formation. Our results shine a rare light on the nanoscale strains in these materials in their technologically relevant device setting.
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May 2024
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I09-Surface and Interface Structural Analysis
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Galo J.
Paez Fajardo
,
Eleni
Fiamegkou
,
James A.
Gott
,
Heng
Wang
,
Israel
Temprano
,
Ieuan D.
Seymour
,
Matthew J. W.
Ogley
,
Ashok S.
Menon
,
Ifan E. L.
Stephens
,
Muhammad
Ans
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Wesley M.
Dose
,
Michaël F. L.
De Volder
,
Clare P.
Grey
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[30201]
Open Access
Abstract: Oxygen loss at high voltages in Ni-rich NMC//graphite Li-ion batteries promotes degradation, but increasing evidence from full cells reveals that the depth of discharge choice can further accelerate aging, i.e., synergistic degradation. In this Letter, we employ cycling protocols to examine the origin of the synergistic degradation for single crystal Ni-rich NMC//graphite pouch cells. In regimes where oxygen loss is not promoted (V < 4.3 V), a lower cutoff voltage does not affect capacity retention (after 100 cycles), despite significant graphite expansion occurring. In contrast, when NMC surface oxygen loss is induced (V > 4.3 V), deeper depth of discharge leads to pronounced faster aging. Using a combination of post-mortem analysis and density functional theory, we present a mechanistic description of surface phase densification and evolution as a function of voltage and cycling. The detrimental impact of this mechanism on lithium-ion kinetics is used to explain the observed cycling results.
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Nov 2023
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[28349, 29728]
Open Access
Abstract: Garnet solid-electrolyte-based Li-metal batteries can be used in energy storage devices with high energy densities and thermal stability. However, the tendency of garnets to form lithium hydroxide and carbonate on the surface in an ambient atmosphere poses significant processing challenges. In this work, the decomposition of surface layers under various gas environments is studied by using two surface-sensitive techniques, near-ambient-pressure X-ray photoelectron spectroscopy and grazing incidence X-ray diffraction. It is found that heating to 500 °C under an oxygen atmosphere (of 1 mbar and above) leads to a clean garnet surface, whereas low oxygen partial pressures (i.e., in argon or vacuum) lead to additional graphitic carbon deposits. The clean surface of garnets reacts directly with moisture and carbon dioxide below 400 and 500 °C, respectively. This suggests that additional CO2 concentration controls are needed for the handling of garnets. By heating under O2 along with avoiding H2O and CO2, symmetric cells with less than 10 Ωcm2 interface resistance are prepared without the use of any interlayers; plating currents of >1 mA cm–2 without dendrite initiation are demonstrated.
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Jul 2023
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I14-Hard X-ray Nanoprobe
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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.
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May 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[127494]
Abstract: Conventional cathodes for Li-ion batteries are layered transition-metal oxides that support Li+ intercalation charge-balanced by redox on the transition metals. Oxidation beyond one electron per transition metal can be achieved in Li-rich layered oxides by involving structural anions, which necessitates high voltages and complex charge compensation mechanisms convoluted by degradation reactions. We report a detailed structural and spectroscopic analysis of the multielectron material Li2Ru0.3Mn0.7O3, chosen due to its low Ru content. Ex situ and operando spectroscopic data over multiple cycles highlight the changing charge compensation mechanism. Notably, over half of the first-cycle capacity is attributed to O2 gas evolution and reversible O redox is minimal. Instead, reduced Ru and Mn species are detected in the bulk and on the surface, which then increasingly contribute to charge compensation as more metal reduction occurs with cycling. Permanent structural changes linked to metal migration are observed with EXAFS and Raman analysis.
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Dec 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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