Synthesis and optical properties of cubic Co3O4 nanoparticles via thermal treatment of a trinuclear cobalt complex

Cubic cobalt oxide nanoparticles with the formula of Co₃O₄ were synthesized via thermal treatment in air, using [Co^II{(µ-L)(µ-OAc)Co^III(NCS)}₂]; [H₂L=salen=1,6-bis(2-hydroxyphenyl)-2,5-diazahexa-1,5-diene]; as precursor. Effect of calcination temperature and citric acid, as emulsifier, was investigated on the phase formation and particle size distribution of the products. Calcination of the precursor at 600 °C in the presence of citric acid results in the formation of Co₃O₄ nanoparticles with the average crystallite size of ∼13 nm. The presence of citric acid provides conditions for the formation of more pure Co₃O₄ crystalline phase with smaller particles. The as-prepared nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), particle size analyzer (PSA), transmission electron microscopy (TEM), UV–vis and Photoluminescence (PL) spectroscopies. The optical property studies indicate that the absorption peaks of Co₃O₄ nanoparticles, prepared in the presence of citric acid, shift towards short wavelengths. This blueshift is related to the quantum size effect.     

Monolayer WxMo1−xS2 Grown by Atmospheric Pressure Chemical Vapor Deposition: Bandgap Engineering and Field Effect Transistors

Monolayer W_x Mo_1?x S₂‐based field effect transistors are demonstrated for the first time on the monolayer W_x Mo_1?x S₂ flake, which is grown by the chemical vapor deposition method under an atmospheric pressure. Detailed material studies using Raman and photoluminescence measurements have been carried out on the as‐grown monolayer W_x Mo_1?x S₂. Electronic band structure of monolayer W_x Mo_1?x S₂ has been calculated using first‐principle theory. The thermal stability of monolayer W_x Mo_1?x S₂ has been evaluated using Raman‐temperature measurement. Carrier transport study on the fabricated W_x Mo_1?x S₂ FETs has been analyzed using temperature‐dependent current measurement, and a field effect mobility of ≈30 cm² V^?1 s^?1 at 300 K is obtained.     

Template‐Assisted Synthesis of Metallic 1T′‐Sn0.3W0.7S2 Nanosheets for Hydrogen Evolution Reaction

Crystal phase control still remains a challenge for the precise synthesis of 2D layered metal dichalcogenide (LMD) materials. The T′ phase structure has profound influences on enhancing electrical conductivity, increasing active sites, and improving intrinsic catalytic activity, which are urgently needed for enhancing hydrogen evolution reaction (HER) activity. Theoretical calculations suggest that metastable T′ phase 2D Sn_1?xW_xS₂ alloys can be formed by combining W with 1T tin disulfide (SnS₂) as a template to achieve a semiconductor‐to‐metallic transition. Herein, 2D Sn_1?xW_xS₂ alloys with varying x are prepared by adjusting the molar ratio of reactants via hydrothermal synthesis, among which Sn_0.3W_0.7S₂ displays a maximum of concentration of 81% in the metallic phase and features a distorted octahedral‐coordinated metastable 1T′ phase structure. The obtained 1T′‐Sn_0.3W_0.7S₂ has high intrinsic electrical conductivity, lattice distortion, and defects, showing a prominently improved HER catalytic performance. Metallic Sn_0.3W_0.7S₂ coupled with carbon black exhibits at least a 215‐fold improvement compared to pristine SnS₂. It has excellent long‐term durability and HER activity. This work reveals a general phase transition strategy by using T phase materials as templates and merging heteroatoms to achieve synthetic metastable phase 2D LMDs that have a significantly improved HER catalytic performance.     

Gate‐Induced Massive and Reversible Phase Transition of VO2 Channels Using Solid‐State Proton Electrolytes

The use of gate bias to control electronic phases in VO₂, an archetypical correlated oxide, offers a powerful method to probe their underlying physics, as well as for the potential to develop novel electronic devices. Up to date, purely electrostatic gating in 3‐terminal devices with correlated channel shows the limited electrostatic gating efficiency due to insufficiently induced carrier density and short electrostatic screening length. Here massive and reversible conductance modulation is shown in a VO₂ channel by applying gate bias V_G at low voltage by a solid‐state proton (H⁺) conductor. By using porous silica to modulate H⁺ concentration in VO₂, gate‐induced reversible insulator‐to‐metal (I‐to‐M) phase transition at low voltage, and unprecedented two‐step insulator‐to‐metal‐to‐insulator (I‐to‐M‐to‐I) phase transition at high voltage are shown. V_G strongly and efficiently injects H⁺ into the VO₂ channel without creating oxygen deficiencies; this H⁺‐induced electronic phase transition occurs by giant modulation (≈7%) of out‐of‐plane lattice parameters as a result of H⁺‐induced chemical expansion. The results clarify the role of H⁺ on the electronic state of the correlated phases, and demonstrate the potentials for electronic devices that use ionic/electronic coupling.     

A Giant Electrocaloric Effect in Nanoscale Antiferroelectric and Ferroelectric Phases Coexisting in a Relaxor Pb0.8Ba0.2ZrO3 Thin Film at Room Temperature

Recently, large electrocaloric effects (ECE) in antiferroelectric sol‐gel PbZr_0.95Ti_0.05O₃ thin films and in ferroelectric polymer P(VDF‐TrFE)55/45 thin films were observed near the ferroelectric Curie temperatures of these materials (495 K and 353 K, respectively). Here a giant ECE (ΔT = 45.3 K and ΔS = 46.9 J K^?1 kg^?1 at 598 kV cm^?1) is obtained in relaxor ferroelectric Pb_0.8Ba_0.2ZrO₃ (PBZ) thin films fabricated on Pt(111)/TiO_x/SiO₂/Si substrates using a sol‐gel method. Nanoscale antiferroelectric (AFE) and ferroelectric (FE) phases coexist at room temperature (290 K) rather than at the Curie temperature (408 K) of the material. The giant ECE in such a system is attributed to the coexistence of AFE and FE phases and a field‐induced nanoscale AFE to FE phase transition. The giant ECE of the thin film makes this a promising material for applications in cooling systems near room temperature.     

Bio‐inspired Synthesis of Protein‐Encapsulated CoPt Nanoparticles

The 24 subunit heat‐shock protein from Methanococcus jannaschii has been genetically altered to display a dodecapeptide on the interior surface that has a strong binding affinity to the L1₀ phase of CoPt (CP_Hsp). Reaction of Co^II and Pt^II salts at 65 °C under reducing conditions results in the formation of a stable CoPt mineral encapsulated within the protein cage. Metallic particles commensurate in size with the interior dimensions of the protein cage (6.5 ± 1.3 nm) have been imaged by transmission electron microscopy and are shown to be surrounded by the intact protein cage. Magnetic measurements performed on the encapsulated nanoparticles exhibit room‐temperature hysteresis on the order of 150 G (1 G = 10^–4 T) prior to annealing and 610 G after annealing at 650 °C.     

Photoinduced Absorption Spectroscopy of CoPi on BiVO4: The Function of CoPi during Water Oxidation

This paper employs photoinduced absorption and electrochemical techniques to analyze the charge carrier dynamics that drive photoelectrochemical water oxidation on bismuth vanadate (BiVO₄), both with and without cobalt phosphate (CoPi) co‐catalyst. These results are correlated with spectroelectrochemical measurements of Co^II oxidation to Co^III in a CoPi/FTO (fluorine doped tin oxide) electrode during dark electrocatalytic water oxidation. Electrocatalytic water oxidation exhibits a non‐linear dependence on Co^III density, with a sharp onset at 1 × 10¹⁷ Co^III cm^?2. These results are compared quantitatively with the degree of CoPi oxidation observed under conditions of photoinduced water oxidation on CoPi–BiVO₄ photoanodes. For the CoPi–BiVO₄ photoanodes studied herein, ≤5% of water oxidation proceeds from CoPi sites, making the BiVO₄ surface the predominant water oxidation site. This study highlights two key factors that limit the ability of CoPi to improve the catalytic performance of BiVO₄: 1) the kinetics of hole transfer from the BiVO₄ to the CoPi layer are too slow to effectively compete with direct water oxidation from BiVO₄; 2) the slow water oxidation kinetics of CoPi result in a large accumulation of Co^III states, causing an increase in recombination. Addressing these factors will be essential for improving the performance of CoPi on photoanodes for solar‐driven water oxidation.     

Micromachining‐Compatible,Facile Fabrication of Polymer Nanocomposite Spin Crossover Actuators

[Fe^II(Htrz)₂(trz)](BF₄) spin crossover particles of 85 nm mean size are dispersed in an SU‐8 polymer matrix and spray‐coated onto silicon microcantilevers. The subsequent photothermal treatment of the polymer resist leads to micrometer thick, smooth, and homogeneous coatings, which exhibit well‐reproducible actuation upon the thermally induced spin transition. The actuation amplitude as a function of temperature is accurately determined by combining integrated piezoresistive detection with external optical interferometry, which allows for the assessment of the associated actuation force (9.4 mN), stress (28 MPa), strain (1.0%), and work density (140 mJ cm^?3) through a stratified beam model. The dynamical mechanical characterization of the films evidences an increase of the resonance frequency and a concomitant decrease of the damping in the high‐temperature phase, which arises due to a combined effect of the thickness and mechanical property changes. The spray‐coating approach is also successfully extended to scale up the actuators for the centimeter range on a polymer substrate providing perspectives for biomimetic soft actuators.     

Searching General Sufficient‐and‐Necessary Conditions for Ultrafast Hydrogen‐Evolving Electrocatalysis

The development of cost‐effective and high‐performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non‐noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high‐spin Co³⁺ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate‐spin Co⁴⁺ sites) in RBaCo₂O_5.5+δ (δ = 1/4; R = lanthanides) can produce a near‐ideal HER reaction path to adsorb H₂O and release H₂, respectively. Experimentally, the as‐synthesized (Gd_0.5La_0.5)BaCo₂O_5.75 outperforms the state‐of‐the‐art Pt/C catalyst in many aspects. The proof‐of‐concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near‐optimal synergistic catalytic effect, which is pivotal for rational design of oxygen‐containing materials.     

Near IR Sensitization of Organic Bulk Heterojunction Solar Cells: Towards Optimization of the Spectral Response of Organic Solar Cells

The spectroscopic response of a poly(3‐hexylthiophene)/[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (P3HT/PCBM)‐based bulk heterojunction solar cell is extended into the near infrared region (NIR) of the spectrum by adding the low bandgap polymer poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b´]‐dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] [PCPDTBT] to the blend. The dominant mechanism behind the enhanced photosensitivity of the ternary blend is found to be a two‐step process: first, an ultrafast and efficient photoinduced charge transfer generates positive charges on P3HT and PCPDTBT and a negative charge on PCBM. In a second step, the positive charge on PCPDTBT is transferred to P3HT. Thus, P3HT serves two purposes. On the one hand it is involved in the generation of charge carriers by the photoinduced electron transfer to PCBM, and, on the other hand, it forms the charge transport matrix for the positive carriers transferred from PCPDTBT. Other mechanisms, such as energy transfer or photoinduced charge transfer directly between the two polymers, are found to be absent or negligible.     

Controllable Synthesis of Nanosized Amorphous MoSx Using Temporally Shaped Femtosecond Laser for Highly Efficient Electrochemical Hydrogen Production

Amorphous molybdenum sulfide (a‐MoS_x) is regarded as a promising electrocatalyst for hydrogen evolution reaction (HER) due to its disorder structures with a significant number of defect‐rich active sites. Here, a green, one‐step, and controllable method is developed to photoregulate the chemical reactions and synthesize nanosized a‐MoS_x by temporally shaped femtosecond laser ablation of ammonium tetrathiomolybdate aqueous solution. By adjusting the laser energy and pulse delay to control photoinduced and/or photothermal‐induced reduction/oxidation, the S to Mo ratio x can be modulated from 1.53 to 3.07 and the ratio of the Mo^V defect species, bridging S₂^2?, and terminal S₂^2? ligands can be controlled. The optimized a‐MoS_x catalysts (x = 2.73) exhibit high catalytic activity with a low Tafel slope of 40 mV dec^?1, high double‐layer capacitance of 74.47 mF cm^?2, and large current density of 516 mA cm^?2 at an overpotential of 250 mV. The high catalytic activity can be mainly attributed to Mo^V defect species and bridging S₂^2? ligands, or most likely dominated by the Mo^V defect species. This study not only provides an alternatively controllable method to prepare a‐MoS_x as efficient HER catalysts but also contributes to the understanding of the origin of its catalytic activity.     

Mixed‐Valence‐Driven Quasi‐1D SnIISnIVS3 with Highly Polarization‐Sensitive UV–vis–NIR Photoresponse

Mixed‐valence states can bring unexpected unique phenomena, especially novel anisotropic physics, due to structural asymmetry, which originate from the discrepant distribution of atoms with different valence. This study reports an unexploited mixed‐valence‐driven quasi‐1D Sn^IISn^IVS₃ crystal, which exhibits widely and distinctively anisotropic polarized‐light absorption reaching ≈3.4 from the deep ultraviolet to near‐infrared region (250–850 nm). The fabricated polarization‐sensitive photodetectors based on highly air‐stable Sn^IISn^IVS₃ nanowires display strong linear dichroism among the UV–vis–NIR spectrum with responsivity exceeding ≈150 A W^?1. Furthermore, the devices are further constructed onto a flexible polyethylene terephthalate (PET) substrate and the photoresponse remains roughly unchanged after repeated bending. This work based on novel mixed‐valence‐driven quasi‐1D ternary sulfide Sn^IISn^IVS₃ excites interest in low‐symmetry semiconductors for developing broadly spectral polarization‐sensitive photodetectors with environmental stability and mechanical flexibility.     

Synergistic Effects of Phase Transition and Electron-Spin Regulation on the Electrocatalysis Performance of Ternary Nitride

Transition metal nitrides (TMNs) have great potential use in energy storage and conversion owing to tunable electronic and bonding characteristics. Novel iron rich nitrides nanoparticles anchored on the N-doped porous carbon, named as (Co_xFe_1–x)₃N@NPC (0 ≤ x < 0.5) are designed here. The synergistic effects of phase transition and electron-spin regulation on oxygen electrocatalysis are testified. A core–shell structure of (Co_xFe_1–x)₃N with high dispersibility is induced by an intermediate phase transition process, which significantly suppresses coarsening of the metallic nitrides. The Co incorporation regulates d-band electrons spin polarization. The t_2g⁵e_g¹ of Fe^II with the ideal e_g electron filling boosts intrinsic activity. (Co_0.17Fe_0.83)₃N@NPC with optimal cobalt content holds electronic configuration with moderate e_g electron filling (t_2g⁵e_g¹), which balances the adsorption of *O₂ and the hydrogenation of *OH, improving bifunctional catalytic performances. Both liquid and solid-state zinc–air batteries assembled based (Co_0.17Fe_0.83)₃N@NPC cathodes substantially deliver higher peak power density and remarkable energy density.     

33% Giant Anomalous Hall Current Driven by Both Intrinsic and Extrinsic Contributions in Magnetic Weyl Semimetal Co3Sn2S2

The anomalous Hall effect (AHE) can be induced by intrinsic mechanisms due to the band Berry phase and extrinsic one arising from the impurity scattering. The recently discovered magnetic Weyl semimetal Co₃Sn₂S₂ exhibits a large intrinsic anomalous Hall conductivity (AHC) and a giant anomalous Hall angle (AHA). The predicted energy dependence of the AHC in this material exhibits a plateau at 1000 Ω^?1 cm^?1 and an energy width of 100 meV just below E_F, thereby implying that the large intrinsic AHC will not significantly change against small‐scale energy disturbances such as slight p‐doping. Here, the extrinsic contribution is successfully triggered from alien‐atom scattering in addition to the intrinsic one of the pristine material by introducing a small amount of Fe dopant to substitute Co in Co₃Sn₂S₂. The experimental results show that the AHC and AHA can be prominently enhanced up to 1850 Ω^?1 cm^?1 and 33%, respectively, owing to the synergistic contributions from the intrinsic and extrinsic mechanisms as distinguished by the TYJ model. In particular, the tuned AHA exhibits a record value among known magnetic materials in low fields. This study opens up a pathway to engineer giant AHE in magnetic Weyl semimetals, thereby potentially advancing the topological spintronics/Weyltronics.     

Novel Multi‐functional Mixed‐oxide Catalysts for Effective NOx Capture,Decomposition, and Reduction

In this paper, novel multi‐functional mixed‐oxide catalysts have been rationally designed and developed for the effective abatement of NO_x. Ca_xCo_{3 – x}Al hydrotalcite‐like compounds (where x = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0) are first synthesized by co‐precipitation and calcined at 800 °C for 4 h in air to derive the mixed oxides. The resultant mixed oxides are generally of spinel phase, where the CaO phase is segregated when x ≥ 2.5. It has subsequently been found that the derived oxides are catalytically multi‐functional for NO_x decomposition, capture, and reduction. For example, the mixed Ca₂Co₁Al₁‐oxide can decompose 55 % NO at 300 °C in 8 % oxygen, completely trap NO for 750 s, and capture 12.88 and 18.06 mg g^–1 NO within 30 and 60 min, respectively. The catalytic activities of the Ca₂Co₁Al₁‐oxide catalyst have been further improved by incorporating La to form a quaternary catalyst Ca₂Co₁La_0.1Al_0.9‐oxide. This catalyst significantly enhances the NO decomposition to 75 %, extends the complete trapping time to 1100 s, and captures more NO at 300 °C in 8 % O₂ (19.02 mg g^–1 NO within 60 min). The in‐situ IR spectra of the catalysts with adsorbed NO indicates that the major nitrogen species formed on the catalysts are various kinds of nitrites and nitrates, which can be readily reduced by H₂ within 6 min at 350 °C. Therefore, the excellent catalytic activity of layered double hydroxide (LDH)‐based mixed oxides for NO decomposition, storage, and reduction can be achieved by the elegant combination of normal transition metals.     

Hexagonal Co9S8: Experimental and Mechanistic Study of Enhanced Electrocatalytic Hydrogen Evolution of a New Crystallographic Phase

The crystallographic phase is one of the most important parameters in determining the physicochemical properties of an electrocatalyst. However, existing understanding of phase-performance relationship is still very limited, especially for unconventional phases. Herein, the experimental discovery of the hexagonal close-packed (hcp) phase of Co₉S₈ is presented. This is the first demonstration of the hexagonal phase of Co₉S₈, and through correlated experimental and computational data, the first to elucidate the origin of enhanced catalytic performance from this new phase. The synthesized Fe doped Co₉S₈-hcp (Fe@Co₉S₈-hcp) catalyst, compared to its face-centered cubic (fcc) phase, exhibits small overpotentials of 44.1 and 298 mV at 10 mA and 500 mA cm⁻² for the hydrogen evolution reaction (HER), respectively. Mass activity is enhanced by 64.9 folds compared to the conventional Co₉S₈-fcc at 300 mV, which is the best among all Co₉S₈-based catalysts ever reported. Density functional theory calculations reveal that the enhanced HER of Fe@Co₉S₈-hcp mainly occurs at the Co sites, which synergizes with the doped Fe playing the role of coordination to strengthen H₂O adsorption and dissociation. This study opens a new avenue for designing high-performance electrocatalysts with unconventional phases for energy and environmental applications.     

Efficient Electron Transfer from an Electron-Reservoir Polyoxometalate to Dual-Metal-Site Metal-Organic Frameworks for Highly Efficient Electroreduction of Nitrogen

Precise design and construction of catalysts with satisfied performance for ambient electrolytic nitrogen reduction reaction (e-NRR) is extremely challenging. By in situ integrating an electron-rich polyoxometalates (POMs) into stable metal organic frameworks (MOFs), five POMs-based MOFs formulated as [Fe_xCo_y(Pbpy)₉(ox)₆(H₂O)₆][P₂W₁₈O₆₂]·3H₂O (abbreviated as Fe_xCo_yMOF-P₂W₁₈) are created and directly used as catalysts for e-NRR. Their electrocatalytic performances are remarkably improved thanks to complementary advantages and promising possibilities of MOFs and POMs. In particular, NH₃ yield rates of 47.04 µg h⁻¹ mg_cat.⁻¹ and Faradaic efficiency of 31.56% by FeCoMOF-P₂W₁₈ for e-NRR are significantly enhanced by a factor of 4 and 3, respectively, compared to the [Fe_0.5Co_0.5(Pbpy)(ox)]₂·(Pbpy)_0.5. The cyclic voltammetry curves, density functional theory calculations and in situ Fourier-transform infrared spectroscopy confirm that there is a directional electron channel from P₂W₁₈ to the MOFs unit to accelerate the transfer of electrons. And the introduction of bimetals Fe and Co in the P₂W₁₈-based MOFs can reduce the energy of the *N₂ to *N₂H step, thereby increasing the production of NH₃. More importantly, this POM in situ embedding strategy can be extended to create other e-NRR catalysts with enhanced performances, which opens a new avenue for future NH₃ production for breakthrough in the bottleneck of e-NRR.     

Diphenylmethanofullerenes: New and Efficient Acceptors in Bulk‐Heterojunction Solar Cells

A novel fullerene derivative, 1,1‐bis(4,4′‐dodecyloxyphenyl)‐(5,6) C₆₁, diphenylmethanofullerene (DPM‐12), has been investigated as a possible electron acceptor in photovoltaic devices, in combination with two different conjugated polymers poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐para‐phenylene vinylene] (OC₁C₁₀‐PPV) and poly[3‐hexyl thiophene‐2,5‐diyl] (P3HT). High open‐circuit voltages, V_OC = 0.92 and 0.65 V, have been measured for OC₁C₁₀‐PPV:DPM‐12‐ and P3HT:DPM‐12‐based devices, respectively. In both cases, V_OC is 100 mV above the values measured on devices using another routinely used fullerene acceptor, [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM). This is somewhat unexpected when taking into account the identical redox potentials of both acceptor materials at room temperature. The temperature‐dependent V_OC reveals, however, the same effective bandgap (HOMO_Polymer–LUMO_Fullerene; HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital) of 1.15 and 0.9 eV for OC₁C₁₀‐PPV and P3HT, respectively, independent of the acceptor used. The higher V_OC at room temperature is explained by different ideality factors in the dark‐diode characteristics. Under white‐light illumination (80 mW cm^–2), photocurrent densities of 1.3 and 4.7 mA cm^–2 have been obtained in the OC₁C₁₀‐PPV:DPM‐12‐ and P3HT:DPM‐12‐based devices, respectively. Temperature‐dependent current density versus voltage characteristics reveal a thermally activated (shallow trap recombination limited) photocurrent in the case of OC₁C₁₀‐PPV:DPM‐12, and a nearly temperature‐independent current density in P3HT:DPM‐12. The latter clearly indicates that charge carriers traverse the active layer without significant recombination, which is due to the higher hole‐mobility–lifetime product in P3HT. At the same time, the field‐effect electron mobility in pure DPM‐12 has been found to be μ_e = 2 × 10^–4 cm² V^–1 s^–1, that is, forty‐times lower than the one measured in PCBM (μ_e = 8 × 10^–3 cm² V^–1 s^–1).     

Passivation of Molecular n‐Doping: Exploring the Limits of Air Stability

Molecular doping is a key technique for flexible and low‐cost organic complementary semiconductor technologies that requires both efficient and stable p‐ and n‐type doping. However, in contrast to molecular p‐dopants, highly efficient n‐type dopants are commonly sensitive to rapid degradation in air due to their low ionization energies (IEs) required for electron donation, e.g., IE = 2.4 eV for tetrakis(1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinato)ditungsten(II) (W₂(hpp)₄). Here, the air stability of various host:W₂(hpp)₄ combinations is compared by conductivity measurements and photoemission spectroscopy. A partial passivation of the n‐doping against degradation is found, with this effect identified to depend on the specific energy levels of the host material. Since host‐W₂(hpp)₄ electronic wavefunction hybridization is unlikely due to confinement of the dopant highest occupied molecular orbital (HOMO) to its molecular center, this finding is explained via stabilization of the dopant by single‐electron transfer to a host material whose energy levels are sufficiently low for avoiding further charge transfer to oxygen–water complexes. Our results show the feasibility of temporarily handling n‐doped organic thin films in air, e.g., during structuring of organic field effect transistors (OFETs) by lithography.     

Temperature‐Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers

Previous investigations of the field‐effect mobility in poly(3‐hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium‐MW: M_n = 7 200 g mol^?1; high‐MW: M_n = 27 000 g mol^?1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse‐radiolysis time‐resolved microwave conductivity (PR‐TRMC) and organic field‐effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra‐grain mobility depends only weakly on MW (being in the order of 10^?2 cm² V^?1 s^?1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature‐dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium‐MW P3HT undergo a “pre‐melting” significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short‐chain P3HT is strongly inhibited by the presence of disordered domains, while in high‐MW P3HT the low‐mobility disordered zones are bridged via inter‐crystalline molecular connections.