I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[17223]
Open Access
Abstract: Mixed 2D/3D perovskite materials are of particular interest to the photovoltaics and light- emitting diode (LED) communities due to their impressive opto-electronic properties alongside improved moisture stability compared to conventional 3D perovskite absorbers. Here, a mixed lead-tin perovskite containing distinct, self-assembled domains of either 3D structures or highly phase-pure Ruddlesden–Popper 2D structures is studied. The complex energy landscape of the material is revealed with ultrafast optical transient absorption measurements. It is shown that charge transfer between these microscale domains only occurs on nanosecond timescales, consistent with the large size of the domains. Using optical pump-terahertz probe spectroscopy, the effective charge-carrier mobility is shown to be an intermediary between analogous pure 2D and 3D perovskites. Furthermore, detailed analysis of the free carrier recombination dynamics is presented. By combining results from a range of excitation wavelengths within a full dynamic model of the photoexcited carrier population, it is shown that the 2D domains in the film exhibit remarkably similar carrier dynamics to the 3D domains, suggesting that long-range charge-transport should not be impeded by the heterogeneous structure of the material.
|
Aug 2023
|
|
DL-SAXS-Offline SAXS and Sample Environment Development
|
Diamond Proposal Number(s):
[32344]
Open Access
Abstract: The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have risen dramatically since the introduction of the “Y-series” of non-fullerene acceptors. However, the demonstration of rapid scalable deposition techniques to deposit such systems is rare. Here, for the first time, we demonstrate the deposition of a Y-series-based system using ultrasonic spray coating─a technique with the potential for significantly faster deposition speeds than most traditional meniscus-based methods. Through the use of an air-knife to rapidly remove the casting solvent, we can overcome film reticulation, allowing the drying dynamics to be controlled without the use of solvent additives, heating the substrate, or heating the casting solution. The air-knife also facilitates the use of a non-halogenated, low-toxicity solvent, resulting in industrially relevant, spray-coated PM6:DTY6 devices with PCEs of up to 14.1%. We also highlight the obstacles for scalable coating of Y-series-based solar cells, in particular the influence of slower drying times on blend morphology and crystallinity. This work demonstrates the compatibility of ultrasonic spray coating, and use of an air-knife, with high-speed, roll-to-roll OSC manufacturing techniques.
|
Jul 2023
|
|
B23-Circular Dichroism
I16-Materials and Magnetism
I22-Small angle scattering & Diffraction
|
Open Access
Abstract: The recently discovered orthorhombic liquid crystal (LC) phase of symmetry Fddd is proving to be widespread. In this work, a chiral hydroxybutyrate linkage is inserted into the molecular core of hexacatenar rodlike compounds, containing a thienylfluorenone fluorophore. In addition to more usual tools, the methods used include grazing-incidence X-ray scattering, modulated differential scanning calorimetry (DSC), flash DSC with rates up to 6000 K/s, and chiro-optical spectroscopies using Mueller matrix method, plus conformational mapping. Although pure R and S enantiomers form only a strongly chiral hexagonal columnar LC phase (Colh*), the racemic mixture forms a highly ordered Fddd phase with 4 right- and 4 left-handed twisted ribbon-like columns traversing its large unit cell. In that structure, the two enantiomers locally deracemize and self-sort into the columns of their preferred chirality. The twisted ribbons in Fddd, with a 7.54 nm pitch, consist of stacked rafts, each containing ∼2 side-by-side molecules, the successive rafts rotated by 17°. In contrast, an analogous achiral compound forms only the columnar phase. The multiple methods used gave a comprehensive picture and helped in-depth understanding not only of the Fddd phase but also of the “parachiral” Colh* in pure enantiomers with irregular helicity, whose chirality is compared to the magnetization of a paramagnet in a field. Unusual short-range ordering effects are also described. An explanation of these phenomena is proposed based on conformational analysis. Surprisingly, the isotropic–columnar transition is extremely fast, completing within ∼20 ms. A clear effect of phase on UV–vis absorption and emission is observed.
|
Jul 2023
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[26630]
Open Access
Abstract: The performance of organic solar cells is strongly governed by the properties of the photovoltaic active layer. In particular, the energetics at the donor (D)–acceptor (A) interface dictate the properties of charge transfer (CT) states and limit the open-circuit voltage. More generally, energetic landscapes in thin films are affected by intermolecular, e.g., van der Waals, dipole, and quadrupole, interactions that vary with D:A mixing ratio and impact energy levels of free charges (ionization energy, electron affinity) and excitons (singlet, CT states). Disentangling how different intermolecular interactions impact energy levels and support or hinder free charge generation is still a major challenge. In this work, we investigate interface energetics of bulk heterojunctions via sensitive external quantum efficiency measurements and by varying the D:A mixing ratios of ZnPc or its fluorinated derivatives and C60. With increasing donor fluorination, the energetic offset between FxZnPc and C60 reduces. Moving from large to low offset systems, we find qualitatively different trends in device performances with D:C60 mixing ratios. We rationalize the performance trends via changes in the energy levels that govern exciton separation and voltage losses. We do so by carefully analyzing shifts and broadening sEQE spectra on a linear and logarithmic scale. Linking this analysis with molecular properties and device performance, we comment on the impact of charge–quadrupole interactions for CT dissociation and free charge generation in our D:C60 blends. With this, our work (1) demonstrates how relatively accessible characterization techniques can be used to probe energy levels and (2) addresses ongoing discussions on future molecular design and optimal D–A pairing for efficient CT formation and dissociation.
|
Jun 2023
|
|
B21-High Throughput SAXS
I07-Surface & interface diffraction
I22-Small angle scattering & Diffraction
|
Abstract: The overall focus of this thesis is investigations into the preferential locations of biomolecules, including membrane proteins, in orientated self-assembled lipid nanostructured materials known as QII phases. The three QII phases, known as the QII G, QII D and QII P , consist of 3 dimensional periodic self-assembled surfaces over which a lipid bilayer is draped. The lipid bilayer in each QII phase consists of regions of flat or high curvature into which it has been hypothesised that guest biomolecules will preferentially partition. Research efforts focus on orientated QII phase domains as more information can be extracted from characteristic Small Angle Scattering (SAS) experiments than from polydomain samples. Different lipid mesophases including the QII phases, were prepared as orientated lipid films and an automated method of 2D Small Angle X-ray Scattering (SAXS) analysis for orientated samples was created. The addition of biomolecules to a QII phase was achieved by co-dissolving with the lipids in an organic solvent before formation of the orientated QII phase, or by addition to an already formed QII phase. Both methods are presented here and the incorporation of various biomolecules into a QII D phase bilayer was monitored in two separate fashions, via SAXS and Raman Spectroscopy. Finally, the addition of biomolecules to orientated QII phases was undertaken and any preferential partitioning into flat or highly curved regions of the bilayer was investigated. It was found via Grazing Incidence Small Angle Neutron Scattering (GISANS) that monopalmitin and cholesterol in a monoolein QII D phase, preferentially partition into the flatter regions of the bilayer. At several instances during my research, variable humidity control was required. Lipid films require particular humidity to maintain specific phase behaviour and for the neutron experiments, the host lipid was contrast matched to a D2O environment. To meet this requirement, two separate humidity control systems were designed and created: the first a low cost, portable, and chamber independent system, the second a fully automated system calibrated to a chamber at Diamond Light Source. A separate study into the relaxed curvature of four lipids, monoolein, monolinolein, phytantriol, and phytantetrol using inverse micelles is also detailed. The relaxed curvature was obtained by calculating the parameters of the neutral surface, or the surface whose area does not change due to bending within a lipid monolayer.
|
Jun 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
|
|
I07-Surface & interface diffraction
|
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.
|
Nov 2022
|
|
I16-Materials and Magnetism
|
Abstract: Materials that undergo a coupled phase transition offer a window into the relationship between electrons, nuclei, and magnetic spins in condensed matter. The development of ultrafast techniques where materials can be probed in the sub-ps time regime have provided the means to provide new insights into the exchanges of energy that occur between these systems. This can be applied to magnetocaloric, memory storage, and spintronics devices. This work investigated the dynamics of the FeRh coupled phase transition, where the magnetic ordering change from Anti-Ferromagnetic (AF) to FerroMagnetic (FM) at temperatures moderately above room temperature. The specific focus of this work is on the structural transformations and the effects of lateral confinement on the transition. An x-ray based probe of anti-parallel Fe spin lattice in the AF phase of FeRh is demonstrated experimentally. Non-resonant x-ray magnetic scattering relies upon long-range spin order being established. We demonstrate the temperature dependence of the long-range ordering and confirm that this order only disappears following complete establishment of the FM moment. As a consequence, it allows for a probe of the mixed AF/FM phase of FeRh. This technique allowed for an estimation of the AF domain size suggesting dimensions are limited by the microstructure of the thin film (~40 nm). Time-resolved X-Ray Diffraction (XRD) studies were carried out at the x-ray Free Electron Laser (x-FEL) at SACLA, Japan. We observed structural changes through the phase transition on a timescale not previously reported and show a fluence dependence that indicates the importance of considering non-equilibrated states in the growth and relaxation dynamics of FeRh. A model is presented which demonstrates that such non-equilibria states can be explained using non-trivial electron-phonon coupling. Complementary heated XRD measurements are consistent with the hypothesis that the paramagnetic phase of FeRh is accessed on ps timescales. The effects of lateral confinement were examined in FeRh nanowire arrays to determine if mesoscale magnetic interactions affect magnetisation dynamics. In order to understand the results obtained, heat dissipation was modelled using finite-element software so as to separate magnetic and thermal contributions. Pump-probe Magneto- Optical Kerr Effect (MOKE) investigations alongside static electrical measurements demonstrate that the orientation of external magnetic fields influences the transition behaviour in FeRh wires. FM stabilisation is observed when the external field is applied along the nanowire length. This orientation dependence was not observed in thin films and is ascribed to the shape anisotropy which may influence the FM domain growth mechanism - shifting the phase transition temperature by up to 10 K at applied magnetic fields of 1 T.
|
Nov 2022
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[17223]
Open Access
Abstract: Mixed-halide mixed-cation hybrid perovskites are among the most promising perovskite compositions for application in a variety of optoelectronic devices due to their high performance, low cost, and bandgap tuning capabilities. Instability pathways such as those driven by ionic migration however continue to hinder their further progress. Here, we use an operando variable-pitch synchrotron Grazing-Incidence Wide-Angle X-ray Scattering technique to track the surface and bulk structural changes in mixed-halide mixed-cation perovskite solar cells under continuous load and illumination. By monitoring the evolution of the material structure, we demonstrate that halide remixing along the electric field and illumination direction during operation hinders phase segregation and limits device instability. Correlating the evolution with directionality- and depth-dependent analyses, we propose that this halide remixing is induced by an electrostrictive effect acting along the substrate out-of-plane direction. However, this stabilizing effect is overwhelmed by competing halide demixing processes in devices exposed to humid air or with poorer starting performance. Our findings shed new light on understanding halide de- and re-mixing competitions and their impact on device longevity. These operando techniques allow real-time tracking of the structural evolution in full optoelectronic devices and unveil otherwise inaccessible insights into rapid structural evolution under external stress conditions.
|
Jul 2022
|
|