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Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	Elucidating and mitigating degradation processes in perovskite light‐emitting diodes Zahra Andaji-Garmaroudi , Mojtaba Abdi-Jalebi , Felix U. Kosasih , Tiarnan Doherty , Stuart Macpherson , Alan R. Bowman , Gabriel J. Man , Ute B. Cappel , Hakan Rensmo , Caterina Ducati , Richard H. Friend , Samuel D. Stranks Advanced Energy Materials 11 DOI: 10.1002/aenm.202002676 Diamond Proposal Number(s): [22668] Show Abstract ▼ Abstract: Halide perovskites have attracted substantial interest for their potential as disruptive display and lighting technologies. However, perovskite light‐emitting diodes (PeLEDs) are still hindered by poor operational stability. A fundamental understanding of the degradation processes is lacking but will be key to mitigating these pathways. Here, a combination of in operando and ex situ measurements to monitor the performance degradation of (Cs0.06FA0.79MA0.15)Pb(I0.85Br0.15)3 PeLEDs over time is used. Through device, nanoscale cross‐sectional chemical mapping, and optical spectroscopy measurements, it is revealed that the degraded performance arises from an irreversible accumulation of bromide content at one interface, which leads to barriers to injection of charge carriers and thus increased nonradiative recombination. This ionic segregation is impeded by passivating the perovskite films with potassium halides, which immobilizes the excess halide species. The passivated PeLEDs show enhanced external quantum efficiency (EQE) from 0.5% to 4.5% and, importantly, show significantly enhanced stability, with minimal performance roll‐off even at high current densities (>200 mA cm−2). The decay half‐life for the devices under continuous operation at peak EQE increases from <1 to ≈15 h through passivation, and ≈200 h under pulsed operation. The results provide generalized insight into degradation pathways in PeLEDs and highlight routes to overcome these challenges.	Nov 2020
I11-High Resolution Powder Diffraction	Bulk fatigue induced by surface reconstruction in layered Ni-rich cathodes for Li-ion batteries Chao Xu , Katharina Märker , Juhan Lee , Amoghavarsha Mahadevegowda , Philip J. Reeves , Sarah J. Day , Matthias F. Groh , Steffen P. Emge , Caterina Ducati , B. Layla Mehdi , Chiu C. Tang , Clare P. Grey Nature Materials 414 DOI: 10.1038/s41563-020-0767-8 Diamond Proposal Number(s): [16733, 25186] Show Abstract ▼ Abstract: Ni-rich layered cathode materials are among the most promising candidates for high-energy-density Li-ion batteries, yet their degradation mechanisms are still poorly understood. We report a structure-driven degradation mechanism for NMC811 (LiNi0.8Mn0.1Co0.1O2), in which a proportion of the material exhibits a lowered accessible state of charge at the end of charging after repetitive cycling and becomes fatigued. Operando synchrotron long-duration X-ray diffraction enabled by a laser-thinned coin cell shows the emergence and growth in the concentration of this fatigued phase with cycle number. This degradation is structure driven and is not solely due to kinetic limitations or intergranular cracking: no bulk phase transformations, no increase in Li/Ni antisite mixing and no notable changes in the local structure or Li-ion mobility of the bulk are seen in aged NMCs. Instead, we propose that this degradation stems from the high interfacial lattice strain between the reconstructed surface and the bulk layered structure that develops when the latter is at states of charge above a distinct threshold of approximately 75%. This mechanism is expected to be universal in Ni-rich layered cathodes. Our findings provide fundamental insights into strategies to help mitigate this degradation process.	Aug 2020
E02-JEM ARM 300CF I14-Hard X-ray Nanoprobe	Performance-limiting nanoscale trap clusters at grain junctions in halide perovskites Tiarnan A. S. Doherty , Andrew J. Winchester , Stuart Macpherson , Duncan N. Johnstone , Vivek Pareek , Elizabeth M. Tennyson , Sofiia Kosar , Felix U. Kosasih , Miguel Anaya , Mojtaba Abdi-Jalebi , Zahra Andaji-Garmaroudi , E. Laine Wong , Julien Madéo , Yu-Hsien Chiang , Ji-Sang Park , Young-Kwang Jung , Christopher E. Petoukhoff , Giorgio Divitini , Michael K. l. Man , Caterina Ducati , Aron Walsh , Paul A. Midgley , Keshav M. Dani , Samuel D. Stranks Nature 580, 360 - 366 DOI: 10.1038/s41586-020-2184-1 Diamond Proposal Number(s): [19023, 19793] Show Abstract ▼ Abstract: Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices. This strong performance (albeit below the practical limits of about 30 per cent and 35 per cent, respectively) is surprising in thin films processed from solution at low-temperature, a method that generally produces abundant crystalline defects. Although point defects often induce only shallow electronic states in the perovskite bandgap that do not affect performance, perovskite devices still have many states deep within the bandgap that trap charge carriers and cause them to recombine non-radiatively. These deep trap states thus induce local variations in photoluminescence and limit the device performance. The origin and distribution of these trap states are unknown, but they have been associated with light-induced halide segregation in mixed-halide perovskite compositions and with local strain, both of which make devices less stable. Here we use photoemission electron microscopy to image the trap distribution in state-of-the-art halide perovskite films. Instead of a relatively uniform distribution within regions of poor photoluminescence efficiency, we observe discrete, nanoscale trap clusters. By correlating microscopy measurements with scanning electron analytical techniques, we find that these trap clusters appear at the interfaces between crystallographically and compositionally distinct entities. Finally, by generating time-resolved photoemission sequences of the photo-excited carrier trapping process, we reveal a hole-trapping character with the kinetics limited by diffusion of holes to the local trap clusters. Our approach shows that managing structure and composition on the nanoscale will be essential for optimal performance of halide perovskite devices.	Apr 2020
I07-Surface & interface diffraction	Controlling the growth kinetics and optoelectronic properties of 2D/3D lead–tin perovskite heterojunctions Edoardo Ruggeri , Miguel Anaya , Krzysztof Galkowski , Geraud Delport , Felix Utama Kosasih , Anna Abfalterer , Sebastian Mackowski , Caterina Ducati , Samuel D. Stranks Advanced Materials DOI: 10.1002/adma.201905247 Diamond Proposal Number(s): [17223] Open Access Show Abstract ▼ Abstract: Halide perovskites are emerging as valid alternatives to conventional photovoltaic active materials owing to their low cost and high device performances. This material family also shows exceptional tunability of properties by varying chemical components, crystal structure, and dimensionality, providing a unique set of building blocks for new structures. Here, highly stable self‐assembled lead–tin perovskite heterostructures formed between low‐bandgap 3D and higher‐bandgap 2D components are demonstrated. A combination of surface‐sensitive X‐ray diffraction, spatially resolved photoluminescence, and electron microscopy measurements is used to reveal that microstructural heterojunctions form between high‐bandgap 2D surface crystallites and lower‐bandgap 3D domains. Furthermore, in situ X‐ray diffraction measurements are used during film formation to show that an ammonium thiocyanate additive delays formation of the 3D component and thus provides a tunable lever to substantially increase the fraction of 2D surface crystallites. These novel heterostructures will find use in bottom cells for stable tandem photovoltaics with a surface 2D layer passivating the 3D material, or in energy‐transfer devices requiring controlled energy flow from localized surface crystallites to the bulk.	Nov 2019
I09-Surface and Interface Structural Analysis	Maximizing and stabilizing luminescence from halide perovskites with potassium passivation Mojtaba Abdi-jalebi , Zahra Andaji-garmaroudi , Stefania Cacovich , Camille Stavrakas , Bertrand Philippe , Johannes M. Richter , Mejd Alsari , Edward P. Booker , Eline M. Hutter , Andrew J. Pearson , Samuele Lilliu , Tom J. Savenije , Hakan Rensmo , Giorgio Divitini , Caterina Ducati , Richard H. Friend , Samuel D. Stranks Nature 555, 497 - 501 DOI: 10.1038/nature25989 Diamond Proposal Number(s): [15841] Show Abstract ▼ Abstract: Metal halide perovskites are of great interest for various high-performance optoelectronic applications. The ability to tune the perovskite bandgap continuously by modifying the chemical composition opens up applications for perovskites as coloured emitters, in building-integrated photovoltaics, and as components of tandem photovoltaics to increase the power conversion efficiency. Nevertheless, performance is limited by non-radiative losses, with luminescence yields in state-of-the-art perovskite solar cells still far from 100 per cent under standard solar illumination conditions. Furthermore, in mixed halide perovskite systems designed for continuous bandgap tunability (bandgaps of approximately 1.7 to 1.9 electronvolts), photoinduced ion segregation leads to bandgap instabilities. Here we demonstrate substantial mitigation of both non-radiative losses and photoinduced ion migration in perovskite films and interfaces by decorating the surfaces and grain boundaries with passivating potassium halide layers. We demonstrate external photoluminescence quantum yields of 66 per cent, which translate to internal yields that exceed 95 per cent. The high luminescence yields are achieved while maintaining high mobilities of more than 40 square centimetres per volt per second, providing the elusive combination of both high luminescence and excellent charge transport. When interfaced with electrodes in a solar cell device stack, the external luminescence yield—a quantity that must be maximized to obtain high efficiency—remains as high as 15 per cent, indicating very clean interfaces. We also demonstrate the inhibition of transient photoinduced ion-migration processes across a wide range of mixed halide perovskite bandgaps in materials that exhibit bandgap instabilities when unpassivated. We validate these results in fully operating solar cells. Our work represents an important advance in the construction of tunable metal halide perovskite films and interfaces that can approach the efficiency limits in tandem solar cells, coloured-light-emitting diodes and other optoelectronic applications.	Mar 2018
I15-Extreme Conditions I22-Small angle scattering & Diffraction	Hybrid glasses from strong and fragile metal-organic framework liquids Thomas Bennett , Jin-chong Tan , Yuanzheng Yue , Emma Baxter , Caterina Ducati , Nicholas Terrill , Hamish Yeung , Zhongfu Zhou , Wenlin Chen , Sebastian Henke , Anthony K. Cheetham , Neville Greaves Nature Communications 6 DOI: 10.1038/ncomms9079 PMID: 26314784 Diamond Proposal Number(s): [9691, 5692] Open Access Show Abstract ▼ Abstract: Hybrid glasses connect the emerging field of metal-organic frameworks (MOFs) with the glass formation, amorphization and melting processes of these chemically versatile systems. Though inorganic zeolites collapse around the glass transition and melt at higher temperatures, the relationship between amorphization and melting has so far not been investigated. Here we show how heating MOFs of zeolitic topology first results in a low density /`perfect/' glass, similar to those formed in ice, silicon and disaccharides. This order-order transition leads to a super-strong liquid of low fragility that dynamically controls collapse, before a subsequent order-disorder transition, which creates a more fragile high-density liquid. After crystallization to a dense phase, which can be remelted, subsequent quenching results in a bulk glass, virtually identical to the high-density phase. We provide evidence that the wide-ranging melting temperatures of zeolitic MOFs are related to their network topologies and opens up the possibility of /`melt-casting/' MOF glasses.	Aug 2015
I06-Nanoscience	Giant and reversible extrinsic magnetocaloric effects in La0.7Ca0.3MnO3 films due to strain X. Moya , L. E. Hueso , F. Maccherozzi , A. I. Tovstolytkin , D. I. Podyalovskii , C. Ducati , L. Phillips , M. Ghidini , O. Hovorka , A. Berger , M. Vickers , E. Defay , S. Dhesi , N. Mathur Nature Materials 12 (1) DOI: 10.1038/NMAT3463 Show Abstract ▼ Abstract: Large thermal changes driven by a magnetic field have been proposed for environmentally friendly energy-efficient refrigeration, but only a few materials that suffer hysteresis show these giant magnetocaloric effects. Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La0.7Ca0.3MnO3 using strain-mediated feedback from BaTiO3 substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications.	Oct 2012

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