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-δ 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 Post‐Treatment of P‐Type and N‐Type Hybrid Organic–Inorganic 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 post‐treatment 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 p‐type Te/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n‐type Ag2Te/PEDOT:PSS hybrid materials is investigated. Primary doping through acid–base 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 X‐ray 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 post‐treatments have on hybrid materials and shows that the impact of these post‐treatments on pure PEDOT:PSS does not always apply to hybrid systems. These new insights into post‐treatment 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 P‑Type Donor–Acceptor Backbone and Poly(3-hexylthiophene) Side Chains Synthesized Via a “Graft Through” Approach

A series of fully conjugated graft copolymers containing poly­(3-hexylthiophene) (P3HT) side chains and a p-type carbazole-diketopyrrolopyrrole (CbzDPP) donor–acceptor 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 UV–visible spectroscopy. The graft copolymers were further investigated using gel permeation chromatography, UV–visible 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 (μ_h ∼ 6 × 10^–4 cm² V^–1 s^–1). 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 (μ_h ∼ 5 × 10^–3 cm² V^–1 s^–1; μ_e ∼ 7 × 10^–4 cm² V^–1 s^–1)

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 poly­(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 UV–vis 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

Annealing‐Induced Chemical Interaction at the Ag/In2O3:H Interface as Revealed by In Situ Photoelectron Spectroscopy

Abstract Hydrogen‐doped 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 light‐emitting devices. However, the corresponding metal/In2O3:H contacts may exhibit undesirably high resistances, significantly deteriorating device performance. To gain insight into the underlying efficiency‐limiting mechanism, hard X‐ray photoelectron spectroscopy is employed to in‐situ monitor annealing‐induced changes in the chemical structure of the Ag/In2O3:H interface system that is further complemented by ex‐situ electron microscopy analyses and contact resistance measurements. The observed evolution of the Ag‐ and In‐related 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 often‐reported deterioration

Structural Aspects of P2‐Type Na 0.67 Mn 0.6 Ni 0.2 Li 0.2 O 2 (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-δ 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

Poly­(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