I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[8117]
Abstract: The crystallization of poly(3-hexylthiophene) (P3HT) to form nanowires has attracted considerable interest because this process significantly increases the hole mobility when compared to amorphous P3HT, leading to improved performance in photovoltaic and other organic electronic devices. However, full characterization of the crystallization self-assembly of the polymer chains in solution has not been achieved yet, due to limited use of
in−situ
not destructive techniques. Here, we investigate the ageing-driven formation and evolution of regioregular (rr) P3HT nanostructures in chlorobenzene solution using small angle neutron scattering (SANS) and UV–Vis spectroscopy. We have monitored how the shape of the rr-P3HT aggregates evolves. The initial states for rr-P3HT chains are the random coils, which straighten to form rods. These subsequently π - π stack to form 2D lamellae, which further stack to create nanowires. The formation of nanowires is promoted both by the length of ageing and by low temperatures (
4∘C
). Temperatures above
>40∘C
reverse the formation of nanowires. Additionally, atomic force microscopy (AFM) and grazing incidence wide angle x-ray scattering (GIWAXS) reveal that the nanowires can be successfully aligned during deposition by off-axis spin coating. Finally, the anisotropic conductivity of the aligned rr-P3HT nanowire films is reported. This is significant for applications such as gas sensing or organic thin film transistors, where increased conductivity and controlled nanostructure are desirable.
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Nov 2019
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[19574]
Abstract: In developing a new compositae air electrode for Solid Oxide Cells (SOCs) it is essential to fully understand the phase chemistry of all components. Ruddlesden-Popper type electrodes such as Pr2NiO4+δ have previously been proposed as attractive alternatives to conventional La0·6Sr0·4Fe0·8Co0·2O3-δ/Ce1-xGdxO2-δ compositae air electrodes for both fuel cell and electrolyser modes of operation. However, Pr2NiO4+δ have been shown to have limited stability, reacting with a Ce1-xGdxO2-δ interlayer to form a Ce1-x-yGdxPryO2-δ (CGPO) phase of unknown stoichiometry. Additionally, Pr2NiO4+δ are known to decompose to Pr4Ni3O10 ± δ under certain conditions.
In this work detailed understanding of the chemical reaction between Pr2NiO4+δ and Ce0.9Gd0.1O2-δ (CGO10) under normal solid oxide cell fabrication and operating temperatures was obtained, identifying the composition of the resulting CGPO phase reaction products. It is shown that, in addition to the unreacted CGO10 present after sintering the compositae at 1100 °C for up to 12 h, a series of CGPO chemical compositions were formed with various Ce, Gd and Pr ratios depending on the relative distance of the doped ceria phases from the Pr2NiO4+δ phases. The extent of the chemical reaction was found to depend on the sintering time and the contact area of the two phases. Further thermal treatment of the resulting products under SOC air electrode operating temperature (800 °C) resulted in the initiation of Pr2NiO4+δ decomposition, forming Pr4Ni3O10 ± δ and Pr6O11 with no detectable change in the composition of previously formed Pr-substituted ceria phases. It is apparent that the Pr2NiO4+δ/CGO10 compositae is unsuitable as an air electrode, but there is evidence that the decomposition products, Pr4Ni3O10 ± δ and Ce1-x-yGdxPryO2-δ are stable and suitable candidates for SOC electrodes.
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Nov 2019
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I07-Surface & interface diffraction
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Abstract: The nanoscale morphology within the photoactive layer of organic solar cells is critical in determining the power conversion efficiency (PCE). Here, we draw attention to the roles of molecular arrangement, and domain size in improving performance, which can be tuned by subjecting the photovoltaic materials to solvent vapor annealing (SVA). In our PTB7-Th:ITIC devices, the PCE can be improved by exposing the device to solvent vapor for 60 s after solution casting. The solvent vapor prolongs reorganizational time and increases molecular ordering and domain size/phase separation, which are sub-optimal in pristine PTB7-Th:ITIC blend films. This improved morphology results in better charge mobility, reduced recombination, and ultimately an improved PCE from 7.1% to 7.9% when using CS2 as the annealing solvent. This simple SVA technique can be applied to a range of OPV systems where the molecular ordering is inferior within the as-cast photoactive layer.
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Oct 2019
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I07-Surface & interface diffraction
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Baocai
Du
,
Renyong
Geng
,
Wei
Li
,
Donghui
Li
,
Yuchao
Mao
,
Mengxue
Chen
,
Xue
Zhang
,
Joel A.
Smith
,
Rachel C.
Kilbride
,
Mary E.
O'kane
,
Dan
Liu
,
David G.
Lidzey
,
Weihua
Tang
,
Tao
Wang
Diamond Proposal Number(s):
[22651]
Abstract: The insufficient phase separation between polymer donors and non-fullerene acceptors (NFAs) featuring with low-structural orders disrupts efficient charge transport and increases charge recombination, consequently limits the maximum achievable power conversion efficiency (PCE) of organic solar cells (OSCs). Herein, an NFA IT-M has been added as the third component into the PBDB-T:m-INPOIC OSCs, and is shown to effectively tune the phase separation between donor and acceptor molecules, although all components in the ternary system exhibit low degrees of structural orders. The incorporation of 10 wt% IT-M into a PBDB-T:m-INPOIC binary host blend appreciably increases the length scale of phase separation, creating continuous pathways which increase and balance charge transport. This leads to an enhanced photovoltaic performance from 12.8% in the binary cell to 13.9% for the ternary cell with simultaneously improved open-circuit voltage, short-circuit current and fill factor. This work highlights the beneficial role of ternary components in controlling the morphology of the active layer for high performance OSCs.
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Sep 2019
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I19-Small Molecule Single Crystal Diffraction
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Wei
Zhang
,
Yong
Hua
,
Linqin
Wang
,
Biaobiao
Zhang
,
Yuanyuan
Liu
,
Peng
Liu
,
Valentina
Leandri
,
Yu
Guo
,
Hong
Chen
,
James M.
Gardner
,
Licheng
Sun
,
Lars
Kloo
Diamond Proposal Number(s):
[15819, 20805]
Abstract: Two zinc-based coordination complexes Y3 and Y4 have been synthesized, characterized and their performance as hole-transport materials (HTMs) for perovskite solar cells (PSCs) have been investigated. The complex Y3 contains two separate ligands, and the molecular structure can be seen as a dis-connected porphyrin ring. On the other hand, Y4 consists of a porphyrin core, and therefore a more extended conjugated system as compared to Y3. The optical and redox properties of the two different molecular complexes are comparable. However, the hole-mobility and conductivity of Y4 as macroscopic material are remarkably higher than that of Y3. Furthermore, when employed as hole-transport materials in perovskite solar cells, cells containing Y4 show a power conversion efficiency (PCE) of 16.05%, comparable to the Spiro-OMeTAD based solar cells with an efficiency around 17.08%. In contrast, solar cells based on Y3 show a negligible efficiency of about 0.01%. The difference in performance of Y3 and Y4 are analyzed and can be attributed to the difference in packing of the non-planar and planar building blocks in the corresponding materials.
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Aug 2019
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I07-Surface & interface diffraction
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Wei
Li
,
Zuo
Xiao
,
Jinlong
Cai
,
Joel A.
Smith
,
Emma L. K.
Spooner
,
Rachel C.
Kilbride
,
Onkar S.
Game
,
Xianyi
Meng
,
Donghui
Li
,
Huijun
Zhang
,
Mengxue
Chen
,
Robert S.
Gurney
,
Dan
Liu
,
Richard A. L.
Jones
,
David
Lidzey
,
Liming
Ding
,
Tao
Wang
Diamond Proposal Number(s):
[120419]
Abstract: The chemical structure of non-fullerene acceptors (NFAs) affects their light-harvesting capabilities, energy levels and molecular orders, all of which play a crucial role in determining the efficiency of organic solar cells (OSCs). In this work, we have systematically investigated a series of ladder-type NFAs having different carbon-oxygen-bridged electron-donating cores, and revealed the effects of core structures and film casting conditions on molecular ordering and performance of OSCs. We found that NFAs containing the thieno [3,2-b]thiophene centered, 6 or 8 fused rings (i.e. COi6DFIC, COi8DFIC) exhibit narrower optical band gaps than NFAs containing the benzene centered, 5 or 7 fused rings (i.e. COi5DFIC, COi7DFIC). NFAs containing less fused rings in the carbon-oxygen-bridged core (i.e. COi5DFIC and COi6DFIC) exhibit edge-on molecular orientation in the blends with face-on oriented PTB7-Th donor, and result in low device efficiency. Although NFAs containing more fused rings (i.e. COi7DFIC and COi8DFIC) possess a pronounced flat-on lamellar crystalline structure in the pure state, the crystallization can be reduced when blending with PTB7-Th and under hot-substrate casting, while the lamella in COi8DFIC can be effectively suppressed to form face-on H- and J-type aggregates, leading to enhanced efficiency.
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Jul 2019
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[4022]
Abstract: Microstructures and pore systems in shales are key to understanding the role of shale in many energy applications. This study proposes a novel multi-stage upscaling procedure to comprehensively investigate the heterogeneous and complex microstructures and pore systems in a laminated and microfractured shale, utilizing 3D multi-scale imaging data. Five imaging techniques were used for characterisation from sub-nanoscale to macroscale (core-scale), spanning four orders of magnitude. Image data collected using X-ray tomography, Focused Ion Beam, and Electron Tomography techniques range in voxel size from 0.6 nm to 13 μm.
Prior to upscaling, a novel two-step analysis was performed to ensure sub-samples were representative. Following this, a three-step procedure, based on homogenising descriptors and computed volume coefficients, was used to upscale the quantified microstructure and pore system. At the highest resolution (nanoscale), four distinct pore types were identified. At the sub-micron scale equations were derived for three pore-associated phases. At the microscale, the volume coefficients were recalculated to upscale the pore system to the macroscale (millimetre). The accuracy of the upscaling methodology was verified, predicting the total porosity within 7.2% discrepancy. The results provide a unique perspective to understand heterogeneous rock types, breaking though prior scale limitations in the pore system.
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Jun 2019
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[18974]
Abstract: Ageing mechanisms in Li‐ion batteries are dependent on the operational temperature but the detailed mechanisms on what processes that takes place at what temperature is still lacking. The electrochemical performance and capacity fading of the common cell chemistry LiNi1/3Mn1/3Co1/3O2 (NMC)/Li4Ti5O12 (LTO) pouch cells is studied at the temperatures: −10 °C, 30 °C and 55 °C. The full cells are cycled with the moderate upper cut‐off potential: 4.3 V vs. Li+/Li. The electrode interfaces are characterized post‐mortem using photoelectron spectroscopy techniques (SOXPES, HAXPES, XANES). Stable cycling at 30 °C is explained by electrolyte reduction forming a stabilizing interphase, thereby preventing further degradation. This initial reaction, between LTO and the electrolyte, seems to be beneficial for the NMC‐LTO full cell. At 55 °C, continuous electrolyte reduction and capacity fading is observed. It leads to formation of a thicker surface layer of organic‐species on the LTO surface than at 30 °C, contributing to an increased voltage hysteresis. At −10 °C, large cell‐resistances are observed, caused by poor electrolyte conductivity in combination with a relatively thicker and LixPFy‐rich surface layer on LTO, which all limit the capacity. ‘Slippage’ with a reduced voltage window showing the loss of active Li+ was observed using XRD.
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May 2019
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[18974]
Abstract: Sodium-ion batteries will have an important role as a complement to lithium-ion in a future where lithium or cobalt, two critical elements for lithium-ion batteries, become scarce or prohibitively expensive. Their implementation depends on the development of high-performing electrode materials based on inexpensive precursors and scalable methods. Phosphorus is a promising candidate as an anode for sodium-ion batteries because of its low potential and high specific capacity. However, it has an extremely low electronic conductivity of 10-14 S cm-1. Furthermore, its 490% volume expansion on sodiation leads to particle pulverization, which substantially reduces the cycle life of the material. Current strategies for improving phosphorus anode performance have focused on synthesizing phosphorus-carbon composites to the exclusion of studying how to improve cycle life by controlling particle size. Here we report an inexpensive and scalable wet-milling method to reduce and tune the particle size of phosphorus to the nanoscale. Phosphorus-carbon composites prepared by ball milling the smallest phosphorus particles with graphite for 48 h delivered 1,354 mA h g-1 with high coulombic efficiency (>99%) and cyclability (88% capacity retention after 100 cycles). These results are an important step in the development of cyclable, high-capacity anodes for sodium-ion batteries.
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Apr 2019
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Abstract: Hybrid organic–inorganic halide perovskites are promising materials for thin-film solar cells. However, the toxicity and instability of best-in-class lead–halide perovskite materials make them nonideal. To combat these issues, we replaced lead with bismuth and explored the sensitivity of these new lead-free materials to the valency and bonding of their cationic organic groups. Specifically, we synthesized and characterized the materials properties and photophysical properties of hexane-1,6-diammonium bismuth pentaiodide ((HDA2+)BiI5) and compared them to an analogue containing a more volatile organic group with half the number of carbon and nitrogen atoms in the form of n-propylammonium ((PA+)xBiI3+x, where 1 < x < 3). The full crystallographic structures of (HDA2+)BiI5 and (PA+)xBiI3+x were resolved by single-crystal X-ray diffraction. (HDA2+)BiI5 was shown to be pure-phase and have a one-dimensional structure, whereas (PA+)xBiI3+x was shown to be a mix of one-dimensional and zero-dimensional phases. Structures of the materials were confirmed by synchrotron X-ray diffraction of powders. Both (HDA2+)BiI5 and (PA+)xBiI3+x exhibit steady-state photoluminescence at room temperature. Density functional theory calculations of (HDA2+)BiI5 predict electronic absorption features and a ∼2 eV bandgap that are consistent with those observed experimentally. Structure–property relationships of the materials were examined, and moisture tolerance and film quality were found to be superior for dication-containing (HDA2+)BiI5 in relation to monocation-containing (PA+)xBiI3+x. We hypothesize that these trends are in part due to a molecular bridging effect enabled by the presence of the dicationic hexanediammonium groups in (HDA2+)BiI5. Solar cells fabricated using (HDA2+)BiI5 as the photoactive layer exhibited photovoltaic action while those containing (PA+)xBiI3+x did not, suggesting that organic dicationic groups are beneficial to light-absorber morphology and ultimately solar-cell performance.
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Feb 2019
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