Tunable Dopants with Intrinsic Counterion Separation Reveal the Effects of Electron Affinity on Dopant Intercalation and Free Carrier Production in Sequentially Doped Conjugated Polymer Films

Carrier mobility in doped conjugated polymers is limited by Coulomb interactions with dopant counterions. This complicates studying the effect of the dopant's oxidation potential on carrier generation because different dopants have different Coulomb interactions with polarons on the polymer backbone. Here, dodecaborane (DDB)‐based dopants are used, which electrostatically shield counterions from carriers and have tunable redox potentials at constant size and shape. DDB dopants produce mobile carriers due to spatial separation of the counterion, and those with greater energetic offsets produce more carriers. Neutron reflectometry indicates that dopant infiltration into conjugated polymer films is redox‐potential‐driven. Remarkably, X‐ray scattering shows that despite their large 2‐nm size, DDBs intercalate into the crystalline polymer lamellae like small molecules, indicating that this is the preferred location for dopants of any size. These findings elucidate why doping conjugated polymers usually produces integer, rather than partial charge transfer: dopant counterions effectively intercalate into the lamellae, far from the polarons on the polymer backbone. Finally, it is shown that the IR spectrum provides a simple way to determine polaron mobility. Overall, higher oxidation potentials lead to higher doping efficiencies, with values reaching 100% for driving forces sufficient to dope poorly crystalline regions of the film.     

Redox Poly-Counterion Doped Conducting Polymers for Pseudocapacitive Energy Storage

Conducting polymers (CPs) have been widely studied for electrochemical energy storage. However, the dopants in CPs are often electrochemically inactive, introducing “dead-weight” to the materials. Moreover, commercial-level electrode materials with high mass loadings (e.g., >10 mg cm⁻²) often encounter the problems of inferior electrical and ionic conductivity. Here, a redox-active poly-counterion doping concept is proposed to improve the electrochemical performance of CPs with ultra-high mass loadings. As a study prototype, heptamolybdate anion (Mo₇O₂₄⁶⁻) doped polypyrrole (PPy) is synthesized by electro-polymerization. A 2 mm thick PPy electrode with mass loading of ≈192 mg cm⁻² reaches a record-high areal capacitance of ≈47 F cm⁻², competitive gravimetric capacitance of 235 F g⁻¹, and volumetric capacitance of 235 F cm⁻³. With poly-counterion doping, the dopants also undergo redox reactions during charge/discharge processes, providing additional capacitance to the electrode. The interaction between polymer chains and the poly-counterions enhances the electrical conductivity of CPs. Besides, the poly-counterions with large steric hindrance could act as structural pillars and endow CPs with open structures for facile ion transport. The concept proposed in this work enriches the electrochemistry of CPs and promotes their practical applications.     

Doped Conductive Polymers: Modeling of Polythiophene with Explicitly Used Counterions

The effect of counterions on the properties and structure of conducting polymers was studied by using a series of Cl₃^? doped polythiophenes (PTs) as a case example. Hybrid density functional theory (DFT) with periodic boundary conditions (PBC) at the B3LYP/6–31G(d) level has been used. This is the first theoretical study of infinitely long doped PT using DFT with counterions explicitly taken into account. The balance between charge carrier states was addressed by studying the singlet and triplet state unit cells of differently doped PTs. The relative isomer energies, density of states diagrams, bond length alternation, and charge distribution patterns were analyzed. Interestingly, the position of the counterion is flexible over the polymer chain and the electronic structure of the polymer and, consequently, optical properties are sensitive to the position of the counterion. A bipolaron electronic configuration is preferred at high dopant concentrations (one dopant per six or less thiophene rings) while a polaron pairs configuration is preferred at low dopant concentrations (one dopant per ten or more thiophene rings) which is in line with many experimental observations.     

Ultrathin MoS2 Nanosheets@Metal Organic Framework‐Derived N‐Doped Carbon Nanowall Arrays as Sodium Ion Battery Anode with Superior Cycling Life and Rate Capability

This study reports the design and fabrication of ultrathin MoS₂ nanosheets@metal organic framework‐derived N‐doped carbon nanowall array hybrids on flexible carbon cloth (CC@CN@MoS₂) as a free‐standing anode for high‐performance sodium ion batteries. When evaluated as an anode for sodium ion battery, the as‐fabricated CC@CN@MoS₂ electrode exhibits a high capacity (653.9 mA h g^?1 of the second cycle and 619.2 mA h g^?1 after 100 cycles at 200 mA g^?1), excellent rate capability, and long cycling life stability (265 mA h g^?1 at 1 A g^?1 after 1000 cycles). The excellent electrochemical performance can be attributed to the unique 2D hybrid structures, in which the ultrathin MoS₂ nanosheets with expanded interlayers can provide shortened ion diffusion paths and favorable Na⁺ insertion/extraction space, and the porous N‐doped carbon nanowall arrays on flexible carbon cloth are able to improve the conductivity and maintain the structural integrity. Moreover, the N‐doping‐induced defects also make them favorable for the effective storage of sodium ions, which enables the enhanced capacity and rate performance of MoS₂.     

Optimization of Von Mises Stress Distribution in Mesoporous α‐Fe2O3/C Hollow Bowls Synergistically Boosts Gravimetric/Volumetric Capacity and High‐Rate Stability in Alkali‐Ion Batteries

Hollow structures are often used to relieve the intrinsic strain on metal oxide electrodes in alkali‐ion batteries. Nevertheless, one common drawback is that the large interior space leads to low volumetric energy density and inferior electric conductivity. Here, the von Mises stress distribution on a mesoporous hollow bowl (HB) is simulated via the finite element method, and the vital role of the porous HB structure on strain‐relaxation behavior is confirmed. Then, N‐doped‐C coated mesoporous α‐Fe₂O₃ HBs are designed and synthesized using a multistep soft/hard‐templating strategy. The material has several advantages: (i) there is space to accommodate strains without sacrificing volumetric energy density, unlike with hollow spheres; (ii) the mesoporous hollow structure shortens ion diffusion lengths and allows for high‐rate induced lithiation reactivation; and (iii) the N‐doped carbon nanolayer can enhance conductivity. As an anode in lithium‐ion batteries, the material exhibits a very high reversible capacity of 1452 mAh g^?1 at 0.1 A g^?1, excellent cycling stability of 1600 cycles (964 mAh g^?1 at 2 A g^?1), and outstanding rate performance (609 mAh g^?1 at 8 A g^?1). Notably, the volumetric specific capacity of composite electrode is 42% greater than that of hollow spheres. When used in potassium‐ion batteries, the material also shows high capacity and cycle stability.     

n‐Doping of a Low‐Electron‐Affinity Polymer Used as an Electron‐Transport Layer in Organic Light‐Emitting Diodes

n‐Doping electron‐transport layers (ETLs) increases their conductivity and improves electron injection into organic light‐emitting diodes (OLEDs). Because of the low electron affinity and large bandgaps of ETLs used in green and blue OLEDs, n‐doping has been notoriously more difficult for these materials. In this work, n‐doping of the polymer poly[(9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,7‐diyl)] (F8BT) is demonstrated via solution processing, using the air‐stable n‐dopant (pentamethylcyclopentadienyl)(1,3,5‐trimethylbenzene)ruthenium dimer [RuCp*Mes]₂. Undoped and doped F8BT films are characterized using ultraviolet and inverse photoelectron spectroscopy. The ionization energy and electron affinity of the undoped F8BT are found to be 5.8 and 2.8 eV, respectively. Upon doping F8BT with [RuCp*Mes]₂, the Fermi level shifts to within 0.25 eV of the F8BT lowest unoccupied molecular orbital, which is indicative of n‐doping. Conductivity measurements reveal a four orders of magnitude increase in the conductivity upon doping and irradiation with ultraviolet light. The [RuCp*Mes]₂‐doped F8BT films are incorporated as an ETL into phosphorescent green OLEDs, and the luminance is improved by three orders of magnitude when compared to identical devices with an undoped F8BT ETL.     

Dual‐Doped Hematite Nanorod Arrays on Carbon Cloth as a Robust and Flexible Sodium Anode

Rechargeable batteries with flexibility can find tremendous applications in wearable and bendable electronics. One central mission for the advancement of such high‐performance batteries is the exploration of flexible anodes with electrochemical and mechanical robustness. Herein reported is a robust and flexible sodium‐ion anode based on self‐supported hematite nanoarray grown on carbon cloth. The ammonia treatment that results in dual doping of both nitrogen and low‐valent iron renders surface reactivity and electric conductivity to the material. The dual‐doped hematite arrays afford a robust activity for sodium storage, exhibiting reversible capacities of 895 and 382 mAh g^?1 at current rates of 0.1 and 5 A g^?1, respectively, or 615 and 356 mAh g^?1 by removing the contribution of the substrate. They also sustain 85% of the initial capacity upon 200 cycles at 0.2 A g^?1. To demonstrate the flexibility, full cells composed of a hematite array anode and Na₃V₂(PO₄)₃/C cathode are assembled. The cell is capable of affording an energy density of 201 Wh kg^?1 and sustaining repeated bending without performance decay, demonstrating a significant potential in practical application.     

Synergy of Ion Doping and Spiral Array Architecture on Ti2Nb10O29: A New Way to Achieve High‐Power Electrodes

Ameliorating electronic/ionic transport and structural stability of electrode materials is important to the development of power‐intensive lithium ion batteries. Despite its great potential as a high‐power anode, titanium niobium oxide (Ti₂Nb₁₀O₂₉, TNO) still underperforms due to its unsatisfactory electronic/ionic conductivity. In this work, a powerful synergistic strategy by combining ion doping and spiral array architecture to boost high‐rate performance of TNO is reported. Cr³⁺ doped TNO nanoparticles (Cr‐TNO) of 5–10 nm intimately grow on a conductive vertical graphene@TiC‐C (VGTC) skeleton, forming novel Cr‐TNO@VGTC spiral arrays. The unique spiral growth of TNO is achieved due to the confinement effect of VGTC skeleton. Meanwhile, a more open TNO crystal structure with faster ion transfer paths and enhanced structural stability is realized by Cr³⁺ doping, demonstrated via density functional theory calculation and in situ synchrotron X‐ray diffraction technique. Benefiting from the superior conductive network, enhanced intrinsic electronic/ionic conductivity of Cr‐TNO and reinforced structural stability, the Cr‐TNO@VTC arrays show prominent high‐power performance with a large capacity of 220 mAh g^?1 at 40 C (power density of ≈11 kW kg^?1) and superior durability (91% retention after 500 cycles). This work provides a new path for the construction of widespread high‐power electrodes for fast energy storage.     

Influence of Doping on Structural and Thermoelectric Properties of AgSbSe<Subscript>2</Subscript>

A series of samples with nominal compositions of AgSb_1−x Sn _x Se₂ (with x = 0.0, 0.1, 0.2, and 0.3) and AgSbSe_2−y Te _y (with y = 0.0, 0.25, 0.5, 0.75, and 1.0) were prepared. The crystal structure of both single crystals and polycrystalline samples was analyzed using x-ray and neutron diffractometry. The electrical conductivity, thermal conductivity, and Seebeck coefficient were measured within the temperature range from 300 K to 700 K. In contrast to intrinsic AgSbSe₂, samples doped with Sn and Te exhibit apparent semiconducting properties (E _g = 0.3 eV to 0.5 eV), lower electrical conductivity, and higher values of the Seebeck coefficient for a small amount of Sn (x = 0.1). Further doping leads to decrease of the thermoelectric power and increase of the electrical conductivity. In order to explain electron transport behavior observed in pure and doped AgSbSe₂, electronic structure calculations were performed by the Korringa–Kohn–Rostoker method with coherent potential approximation (KKR–CPA).     

Enhancing Ultrafast Lithium Ion Storage of Li4Ti5O12 by Tailored TiC/C Core/Shell Skeleton Plus Nitrogen Doping

It is of great importance to reinforce electronic and ionic conductivity of Li₄Ti₅O₁₂ electrodes to achieve fast reaction kinetics and good high‐power capability. Herein, for the first time, a dual strategy of combing N‐doped Li₄Ti₅O₁₂ (N‐LTO) with highly conductive TiC/C skeleton to realize enhanced ultrafast Li ion storage is reported. Interlinked hydrothermal‐synthesized N‐LTO nanosheets are homogeneously decorated on the chemical vapor deposition (CVD) derived TiC/C nanowires forming binder‐free N‐LTO@TiC/C core–branch arrays. Positive advantages including large surface area, strong mechanical stability, and enhanced electronic/ionic conductivity are obtained in the designed integrated arrays and rooted upon synergistic TiC/C matrix and N doping. The above appealing features can effectively boost kinetic properties throughout the N‐LTO@TiC/C electrodes to realize outstanding high‐rate capability at different working temperatures (143 mAh g^?1/10 C at 25 °C and 122 mAh g^?1/50 C at 50 °C) and notable cycling stability with a capacity retention of 99.3% after 10 000 cycles at 10 C. Moreover, superior high‐rate cycling life is also demonstrated for the full cells with N‐LTO@TiC/C anode and LiFePO₄ cathode. The dual strategy may provoke wide interests in fast energy storage areas and motivate the further performance improvement of power‐type lithium ion batteries (LIBs).     

Electrochemically Nanostructured Polyvinylferrocene/Polypyrrole Hybrids with Synergy for Energy Storage

Unconjugated redox polymers, such as polyvinylferrocene (PVF), have rarely been used for energy storage due to their low intrinsic conductivity. Conducting polymers with conjugated backbones, though conductive, may suffer from insufficient exposure to the electrolyte due to the often formed nonporous structures. The present work overcomes this limitation via simultaneous electropolymerization of pyrrole and electroprecipitation of PVF on electrode surfaces. This synthesis method relies on the π–π stacking interactions between the aromatic pyrrole monomers and the metallocene moieties of PVF. This fabrication process results in a highly porous polymer film, which enhances the ion accessibility to polypyrrole (PPy). PPy serves as a “molecular wire,” improving the electronic conductivity of the hybrid and the utilization efficiency of ferrocene. The PVF/PPy hybrid exhibited a specific capacitance of 514.1 F g^?1 _, which significantly exceeds those of PPy (27.3 F g^?1) and PVF (79.0 F g^?1), respectively. This approach offers an alternative to nanocarbon materials for improving the electronic conductivity of polymer hybrids, and suggests a new strategy for fabricating nanostructured polymer hybrids. This strategy can potentially be applied to various polymers with π‐conjugated backbones and redox polymers with metallocene moieties for applications such as energy storage, sensing, and catalysis.     

Annealing effects on physical properties of doped CdTe thin films for photovoltaic applications

Polycrystalline Cadmium Telluride (CdTe) thin films were prepared on glass substrates by thermal evaporation at the chamber ambient temperature and then annealed for an hour in vacuum ~1×10⁻⁵ mbar at 400 °C. These annealed thin films were doped with copper (Cu) via ion exchange by immersing these films in Cu (NO₃)₂ solution (1 g/1000 ml) for 20 min. Further these films were again annealed at different temperatures for better diffusion of dopant species. The physical properties of an as doped sample and samples annealed at different temperatures after doping were determined by using energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD), Raman spectroscopy, transmission spectra analysis, photoconductivity response and hot probe for conductivity type. The optical band gap of these thermally evaporated Cu doped CdTe thin films was determined from the transmission spectra and was found to be in the range 1.42–1.75 eV. The direct energy band gap was found annealing temperatures dependent. The absorption coefficient was >10⁴ cm⁻¹ for incident photons having energy greater than the band gap energy. Optical density was observed also dependent on postdoping annealing temperature. All samples were found having p-type conductivity. These films are strong potential candidates for photovoltaic applications like solar cells.     

A comparison of two air-stable molecular n-dopants for C60

We compare two air-stable n-dopants for the fullerene C₆₀: AOB and DMBI-POH. Conductivity and Seebeck coefficient measurements were performed at various doping concentrations and the thermal activation of the conductivity was determined. A superlinear increase of conductivity upon doping was found for DMBI-POH doped C₆₀ reaching a maximum conductivity of 5.3 S/cm. In contrast to this, a linear rise of conductivity and an exponential thermal activation of mobility was observed for C₆₀ doped by AOB. This suggests a different doping mechanism for the two compounds.     

Properties of highly conducting nitrogen-plasma-doped ZnSe:N thin films

Values for the acceptor ionization energy, E_a, and compensating donor ionization energy, E_d, have been obtained from an analysis of variable-temperature photoluminescence data taken for a series of highly conducting nitrogen-plasma doped ZnSe thin films. E_awas found to be highly temperature dependent, with values ranging from E_a ~110 meV at low temperatures to ~60 meV at room temperature. The compensating donor ionization energy ranged from E_d ~31 meV at low temperatures to ~24 meVat room temperature. These results provide clear evidence of thenonhydrogenic nature of the nitrogen acceptor state in heavily doped ZnSe:N thin films and suggest that interstitial bonding of N, at two or more stable sites, may play a central role in the p-type doping and compensation of this material at high doping levels.     

On the behavior of Bi in a CdTe lattice and the compensation effect in CdTe:Bi

CdTe crystals of two types have been grown by the vertical Bridgman method: (i) crystals doped with Bi to ～10¹⁸ cm^?3 and (ii) double-doped (Bi + Cl) crystals with a Bi concentration of ～10¹⁸ cm^?3 and a Cl concentration of ～10¹⁷ cm^?3. The temperature dependences of the resistivity, photoconductivity, and low-temperature photoluminescence are investigated for the crystals grown. Analysis has shown that doping with Bi (crystals of the first type) leads to compensation of the material. The resistivity of the CdTe:Bi samples at room temperature, depending on the doping level, is varied in the range of 10⁵–10⁹ Ω cm. The hole concentration is determined by the acceptor level at E _v + 0.4 eV in lightly doped CdTe:Bi samples and by the deep center at E _v + 0.72 eV in heavily doped CdTe:Bi samples. Double doping leads to inversion of the conductivity type and reduces the resistivity to ～1 Ω cm. Heavily doped CdTe:Bi crystals and double-doped crystals exhibit the presence of acceptors with an ionization energy of 36 meV, which is atypical of CdTe.     

Activating Basal Planes of NiPS3 for Hydrogen Evolution by Nonmetal Heteroatom Doping

NiPS₃, one of the most promising catalysts among transition metal trichalcogenidophosphates (MTPs) in hydrogen evolution reaction (HER) electrocatalysis, is still inhibited by its unsatisfactory activity originating from its semiconducting nature and inert basal plane. Here, it is proposed, for the first time, to engineer the basal surface activity of NiPS₃ by nonmetal heteroatom doping, and predict that the degree to which the valance band of NiPS₃ is filled dominates not only the electrical conductivity of the catalyst, but also the strength of hydrogen adsorption at its surface. Direct experimental evidence is offered that in all the single nonmetal doping samples, C‐doped NiPS₃ exhibits the optimum activity owing to its moderate filled state of valance band and that C, N codoping even shows Pt‐like activity with an ultralow overpotential of 53.2 mV to afford 10 mA cm^?2 current density and a high exchange current density of 0.7 mA cm^?2 in 1 m KOH. The findings that less valance electrons of dopants than substitutional atoms are of pivotal importance for improving HER activity of NiPS₃ catalyst pave the way for readily designing novel MTPs of ever high performance to replace the incumbent Pt‐based catalysts.     

Investigation on the doping of Polyacetylene Films

We have investigated the oxydation and iodination of (CH)_x-films and found that iodine doped samples degrade in oxygen at a lower rate than pure samples. The iodination can be described as a diffusion process, the diffusion constant being D ≈ 10^-14 − 10⁻¹³ cm²/sec. This value for D is by many orders of magnitude smaller than those normally encountered for diffusion of gases in polymers. The insulator-metal transition, observed at high iodine concentrations, was investigated by optical transmission measurements. The results show that the forbidden gap remains roughly unaffected if the conductivity changes from the semiconducting to the metallic state. Also, below the gap a peak in absorption builds up with increasing iodine concentration but no absorption characteristic for free carriers is observed. These experimental observations are of importance for the selection of models which are to describe the insulator-metal transition and some consequences hereof are discussed.     

Enhanced Thermoelectric Properties of Cu2SnSe3 by (Ag,In)‐Co‐Doping

Dense bulk samples of (Ag,In)‐co‐doped Cu₂SnSe₃ have been prepared by a fast and one‐step method of combustion synthesis, and their thermoelectric properties have been investigated from 323 to 823 K. The experimental results show that Ag‐doping at Cu site remarkably enhances the Seebeck coefficient, reduces both electrical and thermal conductivities, and finally increases the figure of merit (ZT) value. The ZT of the Cu_1.85Ag_0.15SnSe₃ sample reaches 0.80 at 773 K, which is improved by about 70% compared with the unadulterated sample (ZT = 0.46 at 773 K). First principle calculation indicates that Ag‐doping changes the electronic structure of Cu₂SnSe₃ and results in larger effective mass of carriers, thus enhancing the Seebeck coefficient and reducing the electrical conductivity. The low electrical conductivity caused by Ag‐doping can be repaired by accompanying In‐doping at Sn site, and by (Ag,In)‐co‐doping the thermoelectric properties are further promoted. The (Ag,In)‐co‐doped sample of Cu_1.85Ag_0.15Sn_0.9In_0.1Se₃ shows the maximum ZT of 1.42 at 823 K, which is likely the best result for Cu₂SnSe₃‐based materials up to now. This work indicates that co‐doping may provide an effective solution to optimize the conflicting material properties for increasing ZT.     

Conductivity anisotropy in the doped Bi2Te3 single crystals

Temperature dependences (temperature range T = 0.5?300 K) of resistivity in the plane of layers and in the direction perpendicular to the layers, and the galvanomagnetic effects in undoped and doped Bi₂Te₃ single crystals are studied (magnetic field H < 80 kOe, T = 0.5?4.2 K). It is shown that upon doping of Bi₂Te₃ with the Group III atoms (In and B), conductivity anisotropy increases mainly due to an increase in resistivity in the direction perpendicular to the layers. This fact makes it possible to assume that the atoms of these impurities are incorporated mainly into the van der Waal gaps between the layers upon doping. It is also revealed that, upon doping of Bi₂Te₃ with In and B, the temperature dependence of conductivity becomes weaker, which indicates an increase in the role of scattering by defects in scattering mechanisms. The concentrations and mobilities of charge carriers, values of the Hall factor conditioned by the anisotropy of effective masses and orientation of ellipsoids with respect to crystallographic axes, areas of the extreme section of the Fermi surface by the plane perpendicular to the direction of the magnetic field, and the Fermi energy are evaluated.     

Studies of Functional Defects for Fast Na‐Ion Conduction in Na3−yPS4−xClx with a Combined Experimental and Computational Approach

All‐solid‐state rechargeable sodium (Na)‐ion batteries are promising for inexpensive and high‐energy‐density large‐scale energy storage. In this contribution, new Na solid electrolytes, Na_3?yPS_4?xCl_x, are synthesized with a strategic approach, which allows maximum substitution of Cl for S (x = 0.2) without significant compromise of structural integrity or Na deficiency. A maximum conductivity of 1.96 mS cm^?1 at 25 °C is achieved for Na_3.0PS_3.8Cl_0.2, which is two orders of magnitude higher compared with that of tetragonal Na₃PS₄ (t‐Na₃PS₄). The activation energy (E_a) is determined to be 0.19 eV. Ab initio molecular dynamics simulations shed light on the merit of maximizing Cl‐doping while maintaining low Na deficiency in enhanced Na‐ion conduction. Solid‐state nuclear magnetic resonance (NMR) characterizations confirm the successful substitution of Cl for S and the resulting change of P oxidation state from 5+ to 4+, which is also verified by spin moment analysis. Ion transport pathways are determined with a tracer‐exchange NMR method. The functional detects that promote Na ‐ion transport are maximized for further improvement in ionic conductivity. Full‐cell performance is demonstrated using Na/Na_3.0PS_3.8Cl_0.2/Na₃V₂(PO₄)₃ with a reversible capacity of ≈100 mAh g^‐1 at room temperature.