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
,
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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I07-Surface & interface diffraction
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Margherita
Taddei
,
Joel A.
Smith
,
Benjamin M.
Gallant
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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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I11-High Resolution Powder Diffraction
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Harry C.
Sansom
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Leonardo R. V.
Buizza
,
Marco
Zanella
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James T.
Gibbon
,
Michael
Pitcher
,
Matthew S.
Dyer
,
Troy D.
Manning
,
Vinod R.
Dhanak
,
Laura M.
Herz
,
Henry J.
Snaith
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: A newly reported compound, CuAgBiI5, is synthesized as powder, crystals, and thin films. The structure consists of a 3D octahedral Ag+/Bi3+ network as in spinel, but occupancy of the tetrahedral interstitials by Cu+ differs from those in spinel. The 3D octahedral network of CuAgBiI5 allows us to identify a relationship between octahedral site occupancy (composition) and octahedral motif (structure) across the whole CuI–AgI–BiI3 phase field, giving the ability to chemically control structural dimensionality. To investigate composition–structure–property relationships, we compare the basic optoelectronic properties of CuAgBiI5 with those of Cu2AgBiI6 (which has a 2D octahedral network) and reveal a surprisingly low sensitivity to the dimensionality of the octahedral network. The absorption onset of CuAgBiI5 (2.02 eV) barely changes compared with that of Cu2AgBiI6 (2.06 eV) indicating no obvious signs of an increase in charge confinement. Such behavior contrasts with that for lead halide perovskites which show clear confinement effects upon lowering dimensionality of the octahedral network from 3D to 2D. Changes in photoluminescence spectra and lifetimes between the two compounds mostly derive from the difference in extrinsic defect densities rather than intrinsic effects. While both materials show good stability, bulk CuAgBiI5 powder samples are found to be more sensitive to degradation under solar irradiation compared to Cu2AgBiI6.
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Nov 2021
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E02-JEM ARM 300CF
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Mathias
Uller Rothmann
,
Judy S.
Kim
,
Juliane
Borchert
,
Kilian B.
Lohmann
,
Colum M.
O'Leary
,
Alex A.
Sheader
,
Laura
Clark
,
Henry J.
Snaith
,
Michael B.
Johnston
,
Peter D.
Nellist
,
Laura M.
Herz
Diamond Proposal Number(s):
[21734]
Abstract: Hybrid organic-inorganic perovskites have high potential as materials for solar energy applications, but their microscopic properties are still not well understood. Atomic-resolution scanning transmission electron microscopy has provided invaluable insights for many crystalline solar cell materials, and we used this method to successfully image formamidinium lead triiodide [CH(NH2)2PbI3] thin films with a low dose of electron irradiation. Such images reveal a highly ordered atomic arrangement of sharp grain boundaries and coherent perovskite/PbI2 interfaces, with a striking absence of long-range disorder in the crystal. We found that beam-induced degradation of the perovskite leads to an initial loss of formamidinium [CH(NH2)2+] ions, leaving behind a partially unoccupied perovskite lattice, which explains the unusual regenerative properties of these materials. We further observed aligned point defects and climb-dissociated dislocations. Our findings thus provide an atomic-level understanding of technologically important lead halide perovskites.
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Oct 2020
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Abstract: We analyse nucleation-controlled nanocrystal growth in a solution containing surface-binding molecular ligands, which can also nucleate compact layers on the crystal surfaces. We show that if the critical nucleus size for ligands is larger and the nucleation barrier is lower than those for crystal atoms, the ligands nucleate faster than the atoms on relatively wide crystal facets but much slower, if at all, on narrow facets. Such competitive nucleation of ligands and atoms results in ligands covering predominantly wider facets, thus excluding them from the growth process, and acts as a selection mechanism for the growth of crystals with narrower facets, the so-called nanoplatelets. The theory is confirmed by Monte Carlo simulations and validated experimentally for CsPbBr3 nanoplatelets grown from solution. We find that the anisotropic crystal growth is controlled by the growth temperature and the strength of surface bonding for the passivating molecular ligands.
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Jul 2020
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I09-Surface and Interface Structural Analysis
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Theodore D. C.
Hobson
,
Laurie J
Phillips
,
Oliver S
Hutter
,
Huw
Shiel
,
Jack E. N.
Swallow
,
Christopher N.
Savory
,
Pabitra K
Nayak
,
Silvia
Mariotti
,
Bhaskar
Das
,
Leon
Bowen
,
Leanne A. H.
Jones
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Mark A
Farnworth
,
Guillaume
Zoppi
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Henry J.
Snaith
,
Chris
Leighton
,
David O.
Scanlon
,
Vinod R.
Dhanak
,
Ken
Durose
,
Tim D.
Veal
,
Jonathan D
Major
Diamond Proposal Number(s):
[21431]
Open Access
Abstract: The carrier type of Sb2Se3 was evaluated for both thin films and bulk crystals via a range of complementary techniques. X-ray photoelectron spectroscopy (XPS), hot-probe, hall effect and surface photo-voltage spectroscopy showed material synthesized from Sb2Se3 granulate mate-rial to be n-type with chlorine identified as an unintentional n-type dopant via secondary ion mass spectrometry analysis. The validity of chlorine as a dopant was con-firmed by synthesis of intrinsic crystals from metallic precursors and subsequent n-type doping by the addition of MgCl2. Chlorine was also shown to be a substitutional n-type shallow dopant by density functional theory calculations. TiO2/Sb2Se3 n-n isotype heterojunction solar cells of 7.3% efficiency based are demonstrated with band alignment analyzed via XPS.
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Mar 2020
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[17223]
Abstract: Tin-lead mixed metal hybrid perovskites with tunable band gaps are attractive candidates to be used as the low-band gap cell in high efficiency tandem solar cells. Nevertheless, perovskites containing tin have a greater propensity to degrade due to the fast oxidation of Sn2+ to Sn4+, which is a restrictive factor in the development of these materials. Although significant improvements are achieved with Pb:Sn mixed-metal perovskites, in comparison to neat Sn perovskites, the intrinsic instability may still pose a threat to long-term operation. For neat Pb perovskites, two dimensional (2D) hybrid perovskites, where n layers of inorganic material are separated by a long chain organic cation, generally exhibit greater stability but have lower photovoltaic performance characteristics, motivating the study of 2D/3D mixed dimension systems to realize both high efficiency and stability. In this report we demonstrate such optimal compromise between performance and stability using formamidinium, cesium and t-butylammonium as A-site cations with Pb:Sn mixed metal low band gap perovskites. As determined by film structure measurements, the optimised 2D perovskite phases facilitate improved luminescence efficiency, which we infer to be via surface defect site passivation. Perovskite solar cells based on n = 4 and n = 5 lead-tin perovskites achieved power conversion efficiencies of up to 9.3% and 10.6%, respectively and correspondingly retained 47% and 29% of their initial efficiency during storage in nitrogen for 2000 hours. A similar stability trend for n = 4 over n = 5 was also observed for unencapsulated devices during continuous operation under combined air atmosphere and temperature for 10 hours, resulting in improved stability over the 3D lead-tin counterpart.
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Aug 2018
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[12690]
Open Access
Abstract: Hybrid metal halide perovskites are promising new materials for use in solar cells, however, their chemical stability in the presence of moisture remains a significant drawback. Quasi two-dimensional perovskites that incorporate hydrophobic organic interlayers offer improved resistance to degradation by moisture, currently still at the cost of overall cell efficiency. To elucidate the factors affecting the optoelectronic properties of these materials, we have investigated the charge transport properties and crystallographic orientation of mixed methylammonium (MA)/phenylethylammonium (PEA) lead iodide thin films as a function of MA:PEA and thus the thickness of the ‘encapsulated’ MA lead halide layers. We find that monomolecular charge-carrier recombination rates first decrease with increasing PEA fraction, most likely as a result of trap passivation, but then increase significantly as excitonic effects begin to dominate for thin confined layers. Bimolecular and Auger recombination rate constants are found to be sensitive to changes in electronic confinement, which alters the density of states for electronic transitions. We demonstrate that effective charge-carrier mobilities remain remarkably high (near 10 cm2/Vs) for intermediate PEA content and are enhanced for preferential orientation of the conducting lead-iodide layers along the probing electric field. The tradeoff between trap reduction, electronic confinement and layer orientation leads to calculated charge-carrier diffusion lengths reaching a maximum of 2.5 µm for intermediate PEA content (50%).
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Sep 2016
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I09-Surface and Interface Structural Analysis
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Abstract: Organic–inorganic halide perovskite solar cells have rapidly evolved over the last 3 years. There are still a number of issues and open questions related to the perovskite material, such as the phenomenon of anomalous hysteresis in current–voltage characteristics and long-term stability of the devices. In this work, we focus on the electron selective contact in the perovskite solar cells and physical processes occurring at that heterojunction. We developed efficient devices by replacing the commonly employed TiO2 compact layer with fullerene C60 in a regular n–i–p architecture. Detailed spectroscopic characterization allows us to present further insight into the nature of photocurrent hysteresis and charge extraction limitations arising at the n-type contact in a standard device. Furthermore, we show preliminary stability data of perovskite solar cells under working conditions, suggesting that an n-type organic charge collection layer can increase the long-term performance.
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Jun 2015
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