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Charge injection is known as the major source of dark current under an applied reverse bias, which directly influences the performance of organic photodetectors with diode architecture. However, it is unclear which of various contributions, such as electron flow through the junction, shunt leakage, thermionic emission, and tunnelling, are dominant. This study investigates the thermionic emission and tunneling models to describe the origin of experimentally measured dark current generated in an organic photodetector. To elucidate the dominant mechanism, the barrier energies at anodic contacts are set from 0.6 to 1.0 eV using photosensitive layers composed of different acceptors. A linear relation is found between the natural logarithm of the dark current density under reverse bias and the square root of the barrier height, which strongly suggests direct tunneling as dominant mechanism for dark current injection. This conclusion is strengthened by temperature dependent dark current analysis. Further knowledge of the dominant mechanism by charge injection can help devise an effective strategy to suppress dark current for effective organic photodetector device implementation. [ABSTRACT FROM AUTHOR]

Understanding the inherent charge carrier transport mechanism within carbon nanotube-organic hybrid thermoelectric (TE) materials is crucial for enhancing their TE performance. Although various carbon nanotube-organic hybrid TE materials have been developed, the influence of the barrier energy on the TE transport mechanism within these hybrids remains elusive. Our study focuses on the engineering of barrier energy between single-walled carbon nanotubes (SWCNTs) and small organic molecules (SOMs) by modulating the mesomeric effects of terminal functional groups on T-shaped SOMs. The minimization of barrier energy in an SWCNTs- BTBIN hybrid to 0.04 eV resulted in a semiconducting-dominant transport character, facilitating the energy filtering of SWCNTs- BTBIN . Consequently, SWCNTs- BTBIN achieved a higher Seebeck coefficient (65 μV K -1 ) than other hybrids (39-54 μV K -1 ) having steeper barrier energies (0.30 and 0.19 eV), enabling the highest power factor (798 μW m -1 K -2 ) and ZT value up to 0.035 at room temperature among SWCNTs- BTBI hybrid series. A TE module consisting of SWCNTs- BTBIN incorporating five-leg TE elements produced an output power exceeding 0.82 μW, suggesting that integrating barrier energy engineering with analyses of TE transport mechanisms can significantly advance the design of high-performance nanocarbon-based organic hybrid TEs.

Sulfur dioxide (SO2) and carbon dioxide (CO2) removals are of great significance for fossil fuel combustion, where they can be simultaneously captured by calcium‐based absorbents. Nevertheless, the CO2 uptake capacity declines with SO2 partial pressures. This paper aims at explaining the mechanisms of steam‐declined sulfation and steam‐enhanced carbonation by density functional theory calculations. CaO(001) surface is chosen as the absorbent, and the transition state is calculated to obtain the desorption barrier energy of the adsorbates. By analyzing the desorption of the adsorbate on pristine CaO(001) surface and the CaO(001) surface that has adsorbed other adsorbate, it can be concluded that SO2 adsorption inhibits CO2 adsorption since the barrier energy of CO2 desorption on SO2‐CaO(001) surface (24.15 kJ mol–1) is less than CO2 desorption on CaO(001) surface (129.52 kJ mol–1). By comparing the coadsorption energy of the two adsorbates with the sum of the adsorption energy of each adsorbate, it is practical that the H2O adsorption inhibits SO2 adsorption because the calculated coadsorption energy (−221.27 kJ mol–1) is larger than the sum of H2O adsorption energy (–100.00 kJ mol–1) and SO2 adsorption energy (−194.37 kJ mol–1). However, the calculated coadsorption energy of H2O and CO2 adsorption (−254.89 kJ mol–1) is less than the sum of CO2 adsorption energy (−144.23 kJ mol–1) and H2O adsorption energy (−100.00 kJ mol–1), indicating the promotion of CO2 adsorption. Steam in the adsorption process plays the roles of sulfation suppression and carbonation enhancement. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Dissociative adsorption of molecular oxygen (O2) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O2 with Al clusters using density functional theory (DFT) and atom-centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O2 and Al clusters to estimate the barrier energy of this reaction. The M06-2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06-2X functional predicts the reactivity of O2 with the Al cluster in agreement with the experimental findings, that is, singlet O2 readily reacts with Al clusters but triplet O2 is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O2 with Al clusters. The M06-2X functional is relevant for investigating chemical reactions involving Al and O2. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Although numerous thermoelectric materials based on single-walled carbon nanotubes (SWNTs) and organic semiconductors have been reported during the past decade, the correlation between energy levels of organic semiconductors and thermoelectric performances of their hybrids is still ambiguous. In this study, we demonstrate that simultaneous modulation of the bandgap and highest occupied molecular orbital levels in organic small molecules (OSMs) largely improves the Seebeck coefficient and thus maximizes the figure of merit ( ZT ) of SWNT/OSM hybrids. SWNT/ CzS with an enlarged bandgap and reduced barrier energy exhibited a synergistic increment in the Seebeck coefficient (108.7 μV K -1 ) and power factor (337.2 μW m -1 K -2 ), with the best ZT of 0.058 at room temperature among dopant-free carbon nanotube-hybridized thermoelectrics. The efficient charge carrier transport and reduced thermal conductivity of SWNT/ CzS provided enhanced thermoelectric performance. Our strategy based on energy level modulation could be broadly applied for performance enhancement of organic and hybrid thermoelectric materials.

A γ relaxation dielectric loss peak has been measured in the temperature range 113–163 K for a series of epoxy resins based on diglycidyl ether bisphenol-A (DGEBA). The network architecture of the examined systems were systematically altered using varied types of functional network modifiers featuring different functional groups. Analysis of the temperature dependence of the loss peak frequency leads to a radically new interpretation of the fundamental processes that are associated with the γ relaxation. The analysis has shown that the relaxation process can best be described in terms of a thermally assisted tunnelling displacement of a proton, termed activated tunnelling. The parameters derived not only fit the experimental data well, but have a clear physical origin that is shown to be consistent with the network topology as expressed through the glass transition temperature. The maximum temperature for which such behavior is observable has been determined and shown to be consistent with the measurements. The approach proposed here provides a new method for understanding γ relaxations in these and similar systems. Temperature T , dependence of the gamma relaxation frequency f p , for four related epoxy resin formulations. The curvature in the four data sets (◯ △ ▽ &square) is well reproduced by the activated tunnelling best fits (solid, long dash, short dash, dash dot lines), demonstrating that activated tunnelling is a better description than the traditional Arrhenius theory. [Display omitted] • New physical understanding Gamma relaxations. • Thermally assisted proton tunnelling at local sites describes Gamma relaxation. • Activated tunnelling is a better description than the traditional Arrhenius theory. • Tunnelling parameters yield a description of the relaxation site potential surface. • Tunnelling parameters can be correlated with material topological constraints. [ABSTRACT FROM AUTHOR]