10 research outputs found
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Structural Aspects of P2-Type Na0.67Mn0.6Ni0.2Li0.2O2 (MNL) Stabilization by Lithium Defects as a Cathode Material for Sodium-Ion Batteries
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-Ύ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Gmb
Understanding the Effects of Primary and Secondary Doping via PostâTreatment of PâType and NâType Hybrid OrganicâInorganic Thin Film Thermoelectric Materials
Abstract Hybrid organic/inorganic materials have emerged as promising thermoelectric (TE) materials since they inherit the individual strengths of each component, enabling rational materials design with enhanced TE performance. The doping of hybrid TE materials via postâtreatment processes is used to improve their performance, but there is still an incomplete understanding of the elicited effects. Here, the impact of different doping methods on the thin film TE performance of pâtype Te/poly(3,4âethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and nâtype Ag2Te/PEDOT:PSS hybrid materials is investigated. Primary doping through acidâbase and charge transfer processes using H2SO4 and tetrakis(dimethylamino)ethylene, respectively, and the effects of secondary doping using ethylene glycol is examined. Through a combination of Hall effect measurements, hard Xâray photoelectron spectroscopy, and Raman spectroscopy, variations in the charge carrier concentration, mobility, and overall TE performance are related to the morphological and chemical structure of the hybrid materials. This study provides an improved understanding of the effects that different postâtreatments have on hybrid materials and shows that the impact of these postâtreatments on pure PEDOT:PSS does not always apply to hybrid systems. These new insights into postâtreatment effects on hybrid materials is expected to facilitate further enhancement of their performance as electronic materials in general and thermoelectric materials in particular
Fully Conjugated Graft Copolymers Comprising a PâType DonorâAcceptor Backbone and Poly(3-hexylthiophene) Side Chains Synthesized Via a âGraft Throughâ Approach
A series of fully conjugated graft
copolymers containing polyÂ(3-hexylthiophene)
(P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole (CbzDPP)
donorâacceptor backbone were synthesized via a graft through
Suzuki polymerization. The macromonomers were formed by externally
initiating P3HT growth from a boronic ester-functionalized carbazole
via Kumada catalyst transfer polycondensation. Subsequently, this
macromonomer was copolymerized with a DPP monomer via a graft through
Suzuki polymerization to yield the final graft copolymers. The graft
copolymers exhibit optical and electronic properties of both P3HT
and the CbzDPP polymers independently due to the break in conjugation
between the carbazole unit and P3HT chain. Moreover, these properties
reflect the relative proportion of P3HT and CbzDPP polymers; shorter
P3HT chain lengths lead to graft copolymers that possess more CbzDPP
character and vice versa. The macromonomers were characterized by
gel permeation chromatography, mass spectrometry, and UVâvisible
spectroscopy. The graft copolymers were further investigated using
gel permeation chromatography, UVâvisible spectroscopy, cyclic
voltammetry, differential scanning calorimetry, and atomic force microscopy.
Finally, organic field effect transistors were fabricated using the
graft copolymers and compared to an analogous linear CbzDPP copolymer.
Ultimately, the graft copolymers with the longest P3HT chains (ca.
75 repeat units) exhibited almost exclusively P3HT characteristics,
possessing a small CbzDPP internal charge transfer (ICT) peak and
only p-type conductivity (ÎŒ<sub>h</sub> ⌠6 Ă 10<sup>â4</sup> cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>). Conversely, the graft copolymers with the shortest P3HT chains
(ca. 10 repeat units) showed significant CbzDPP character, including
a strong ICT peak and ambipolar mobilities (ÎŒ<sub>h</sub> âŒ
5 Ă 10<sup>â3</sup> cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>; ÎŒ<sub>e</sub> ⌠7 Ă 10<sup>â4</sup> cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>)
Effect of Regioregularity on Charge Transport and Structural and Excitonic Coherence in Poly(3-hexylthiophene) Nanowires
This
study explores the role of very small changes in polyÂ(3-hexylthiophene-2,5-diyl)
(P3HT) regioregularity on the physical and electronic properties of
P3HT nanowires. Due to a high level of synthetic control, we are able
to isolate the effects of regioregularity from those of polymer molecular
weight and dispersity for the first time. A series of P3HTs with regioregularities
from 96 to 99%, similar molecular weights, and low dispersities are
synthesized. The charge transport properties of these polymers, along
with a Soxhlet extracted 93% regioregular P3HT purchased from Rieke
metals, are investigated in both thin film and nanowire transistors.
The resulting structural characteristics are examined by atomic force
microscopy and X-ray diffraction, and the optical characteristics
are explored by UVâvis absorption. It is found that increasing
the P3HT regioregularity results in improved charge transport characteristics,
with an increase in mobility by a factor of 4 for the regioregularities
examined. The increased mobility is shown to reflect increasing structural
coherence lengths in the (010) direction, as well as improved J-aggregate
characteristics due to greater planarity and reduced numbers of defect
sites along the polymer nanowires. Overall, this study serves to emphasize
the importance of determining and reporting even small changes in
polymer regioregularity
AnnealingâInduced Chemical Interaction at the Ag/In2O3:H Interface as Revealed by In Situ Photoelectron Spectroscopy
Abstract Hydrogenâdoped In2O3 (In2O3:H) is highly conductive while maintaining extraordinary transparency, thus making it a very attractive material for applications in optoelectronic devices such as (multijunction) solar cells or lightâemitting devices. However, the corresponding metal/In2O3:H contacts may exhibit undesirably high resistances, significantly deteriorating device performance. To gain insight into the underlying efficiencyâlimiting mechanism, hard Xâray photoelectron spectroscopy is employed to inâsitu monitor annealingâinduced changes in the chemical structure of the Ag/In2O3:H interface system that is further complemented by exâsitu electron microscopy analyses and contact resistance measurements. The observed evolution of the Agâ and Inârelated photoelectron line intensities can be explained by significant intermixing across the Ag/In2O3:H interface. The corresponding lineshape broadening of the Ag 3d spectra is attributed to the formation of Ag2O and AgO, which becomes significant at temperatures above approximately 160 °C. However, after annealing to 300 °C, instead of the formation of an insulating AgOx interfacial layer, it is found i) In to be rather homogeneously distributed in the complete Ag/In2O3:H stack, ii) Ag diffusing into the In2O3:H, and iii) an improvement of the contact resistance rather than its oftenâreported deterioration
Structural Aspects of P2âType Na 0.67 Mn 0.6 Ni 0.2 Li 0.2 O 2 (MNL) Stabilization by Lithium Defects as a Cathode Material for SodiumâIon Batteries
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-ÎŽ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded
Surface-Initiated Synthesis of Poly(3-methylthiophene) from Indium Tin Oxide and its Electrochemical Properties
PolyÂ(3-methylthiophene) (P3MT) was synthesized directly
from indium
tin oxide (ITO) electrodes modified with a phosphonic acid initiator,
using Kumada catalyst transfer polymerization (KCTP). This work represents
the first time that polymer thickness has been controlled in a surface
initiated KCTP reaction, highlighting the utility of KCTP in achieving
controlled polymerizations. Polymer film thicknesses were regulated
by the variation of the solution monomer concentration and ranged
from 30 to 265 nm. Electrochemical oxidative doping of these films
was used to manipulate their near surface composition and effective
work function. Doped states of the P3MT film are maintained even after
the sample is removed from solution and potential control confirming
the robustness of the films. Such materials with controllable thicknesses
and electronic properties have the potential to be useful as interlayer
materials for organic electronic applications