Marcus Charge Transfer Theory Research Articles

Selective methanol production via CO2 reduction on Cu2O revealed by micro-kinetic study combined with constant potential model

High efficiency electrocatalysis of greenhouse gas CO2 to liquid fuel methanol attracts great attentions that allows energy transformation from renewable electric energy to storable chemical energy. Catalytically converting CO2 to methanol using green hydrogen is a promising pathway to achieve carbon neutrality. In this work, the catalytic activity and product selectivity of the electrochemical CO2 reduction reaction on Cu2O were studied using a micro-kinetic model based on Marcus charge transfer theory. The constant potential model under the grand-canonical ensemble enables the accurate description of binding energies and ground-state charge transfer upon surface adsorption as a function of electrode potential. Firstly, the potential-dependent activation energies and rate constants of all possible elementary reactions involved in CO2 reduction are calculated. Then, the surface coverage and its derivative can be obtained in a steady-state approximation. Finally, the total reaction rate and partial reaction rate can be deduced, allowing for direct comparison with catalytic activity (current density) and product selectivity (Faradaic efficiency). It is found that CH3OH is the dominant product on the Cu2O(111) surface, while CO is the main product on the Cu2O(110) surface. Based on the derived total and partial reaction rates under the steady-state approximation, it is demonstrated that Cu2O(111) exhibits the highest electrocatalytic activity and methanol selectivity at U = −0.6 V vs. SHE. This research presents a methodology for predicting apparent electrocatalytic performance from microscopic reaction energy calculations, which can be applied to other important electrocatalytic reaction mechanisms and performance predictions.

Estimation of the Charge Mobility of Phenanthroline derivatives with the view of Density Functional Theory: Reorganization Energy and Charge Transfer Integral are in play

Molecular arrangement and noncovalent interactions in organic materials greatly influence the charge mobility in organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and organic field-effect transistors (OFETs). In the light of the this argument, we examined the electronic properties of the phenanthroline derivatives by considering the charge mobility with the combination of density functional theory and Marcus Charge Transfer Theory. The drift electron mobility of the molecule 1 and 2 were determined to 21.13 cm2 V-1 s-1 and 18.00 cm2 V-1 s-1, respectively through J type π⋯π stacking interactions created by small perpendicular distances between the adjacent rings. The effective charge pathways of the molecules were generated with strong π⋯π stacking interactions consolidated by noncovalent interactions in their solid phases. The electron reorganization energy for both molecules were determined smaller than that of holes which means they have n-type semiconductor properties. The charge transfer integrals were calculated with the optimization of molecules’ dimer configurations that the theoretical results demonstrate the charge transfer integral depends on the distance between the stacking rings. High charge transfer integral and small reorganization energy give the high charge mobility fort he semiconductor molecules. Beside the mobility, energy band gap, ionization potential, electron and hole injection barriers of the molecules were interpreted to further understand their electronic properties. Due to the small LUMO values which provide n-type molecule and small electron injection barrier. From the our work both molecules can be effective n type organic semiconductor devices with the high mobility and can be modified for more efficient charge transport in phenanthroline derivatives.

Mechanism Study of Molecular Trap in All-Organic Polystyrene-Based Dielectric Composite.

It is a huge challenge to explore how charge traps affect the electric breakdown of polymer-based dielectric composites. In this paper, alkane and aromatic molecules with different substituents are investigated according to DFT theoretical method. The combination of strong electron-withdrawing groups and aromatic rings can establish high electron affinity molecules. 4'-Nitro-4-dimethylaminoazobenzene (NAABZ) with a vertical electron affinity of 1.39eV and a dipole moment of 10.15 D is introduced into polystyrene (PSt) to analyze the influence of charge traps on electric properties. Marcus charge transfer theory is applied to calculate the charge transfer rate between PSt and NAABZ. The nature of charge traps is elaborated from a dynamic perspective. The enhanced breakdown mechanism of polymers-based composites stems from the constraint of carrier mobility caused by the change in transfer rate. But the electrophile nature of high electron affinity filler can decrease the potential barriers at the metal-polymer interface. Simultaneously, the relationship between the electron affinity of fillers and the breakdown strength of polymer-based composites is nonlinear because of the presence of the inversion region. Based on the deep understanding of the molecular trap, this work provides the theoretical calculation for the design and development of high-performance polymer dielectrics.

Protein charge transfer far from equilibrium: a theoretical perspective.

Potential differences for protein-assisted electron transfer across lipid bilayers or in bio-nano setups can amount to several 100 mV; they lie far outside the range of linear response theory. We describe these situations by Pauli-master equations that are based on Marcus theory of charge transfer between self-trapped electrons and that obey Kirchhoff's current law. In addition, we take on-site blockade effects and a full non-linear response of the local potentials into account. We present analytical and numerical current-potential curves and electron populations for multi-site model systems and biological electron transfer chains. Based on these, we provide empirical rules for electron populations and chemical potentials along the chain. The Pauli-master mean-field results are validated by kinetic Monte Carlo simulations. We briefly discuss the biochemical and evolutionary aspects of our findings.

The mechanism of improving germanium metal–oxide–semiconductor field-effect transistors’ reliability by high-k dielectric and yttrium-doping: From the view of charge trapping

The application of germanium (Ge)-based transistors has long been restricted by the poor reliability of the gate dielectrics. One solution proposed in the experiment is capping the GeO2 layer with high-k dielectrics and further doping the dielectric with yttrium (Y) atoms. However, the strategy only works at a very small doping concentration window, and the underlying mechanism remains unclear. Here, we carry out first-principles calculations on a concrete Ge/GeO2/ZrO2 stack to study the structural and electronic properties of various defects before and after Y-doping and further calculate their exact charge-trapping rates by the Marcus charge transfer theory. We show that the Y atoms can effectively weaken the charge-trapping capability of vacancy defects in the ZrO2 layer, but on the other hand, they can induce some new types of active defects if the density is high. In addition, it is found that the Y atoms can have a very different effect even when doped to the same material. These results indicate that a precise control of the doping position and doping concentration is necessary to promote the reliability of Ge transistors.

Theoretical exploration of diverse electron-deficient core and terminal groups in A–DA′D–A type non-fullerene acceptors for organic solar cells

The influences triggered by the structurally diverse electron-withdrawing terminal group and fuse-ring electron-deficient core on the performance of NFAs OSCs are comprehensively investigated by using DFT, TD-DFT and Marcus charge transfer theory.

Defects Induced Charge Trapping/Detrapping and Hysteresis Phenomenon in MoS2 Field-Effect Transistors: Mechanism Revealed by Anharmonic Marcus Charge Transfer Theory

One critical problem inhibiting the application of MoS2 field-effect transistors (FETs) is the hysteresis in their transfer characteristics, which is typically associated with charge trapping (CT) and charge detrapping (CDT) induced by atomic defects at the MoS2-dielectric interface. Here, we propose a novel atomistic framework to simulate electronic processes across the MoS2-SiO2 interface, demonstrating the distinct CT/CDT behavior of different types of atomic defects and further revealing the defect type(s) that most likely cause hysteresis. An anharmonic approximation of the classical Marcus theory is developed and combined with state-of-the-art density functional theory to calculate the gate bias-dependent CT/CDT rates. All the key electronic quantities are calculated with Heyd-Scuseria-Ernzerhof hybrid functionals. The results show that single Si-dangling bond defects are active electron trapping centers. Single O-dangling bond defects are active hole trapping centers, which are more likely to be responsible for the hysteresis phenomenon due to their significant CT rate and apparent threshold voltage shift. In contrast, double Si-dangling bond defects are not active trap centers. These findings provide fundamental physical insights for understanding the hysteresis behavior of MoS2 FETs and provide vital support for understanding and solving the reliability of nanoscale devices.

Local Electric Field Controls Fluorescence Quantum Yield of Red and Far-Red Fluorescent Proteins.

Genetically encoded probes with red-shifted absorption and fluorescence are highly desirable for imaging applications because they can report from deeper tissue layers with lower background and because they provide additional colors for multicolor imaging. Unfortunately, red and especially far-red fluorescent proteins have very low quantum yields, which undermines their other advantages. Elucidating the mechanism of nonradiative relaxation in red fluorescent proteins (RFPs) could help developing ones with higher quantum yields. Here we consider two possible mechanisms of fast nonradiative relaxation of electronic excitation in RFPs. The first, known as the energy gap law, predicts a steep exponential drop of fluorescence quantum yield with a systematic red shift of fluorescence frequency. In this case the relaxation of excitation occurs in the chromophore without any significant changes of its geometry. The second mechanism is related to a twisted intramolecular charge transfer in the excited state, followed by an ultrafast internal conversion. The chromophore twisting can strongly depend on the local electric field because the field can affect the activation energy. We present a spectroscopic method of evaluating local electric fields experienced by the chromophore in the protein environment. The method is based on linear and two-photon absorption spectroscopy, as well as on quantum-mechanically calculated parameters of the isolated chromophore. Using this method, which is substantiated by our molecular dynamics simulations, we obtain the components of electric field in the chromophore plane for seven different RFPs with the same chromophore structure. We find that in five of these RFPs, the nonradiative relaxation rate increases with the strength of the field along the chromophore axis directed from the center of imidazolinone ring to the center of phenolate ring. Furthermore, this rate depends on the corresponding electrostatic energy change (calculated from the known fields and charge displacements), in quantitative agreement with the Marcus theory of charge transfer. This result supports the dominant role of the twisted intramolecular charge transfer mechanism over the energy gap law for most of the studied RFPs. It provides important guidelines of how to shift the absorption wavelength of an RFP to the red, while keeping its brightness reasonably high.

A DFT study on the electronic and photophysical properties of biphenylyl/thiophene derivatives for organic light emitting transistors

A theoretical study was carried out to understand the geometrical, electronic and optical properties of bipheylyl/thiophene based molecular system. For that, density functional theory along with classical Marcus charge transfer theory and time-dependent potentials were used. The results indicate that the structure-property relationship between the molecular parameters and ionization energy, electron affinity, reorganization energy, charge transfer integrals, mobility, energy gap, optical absorption and transition dipole moments. Low lying HOMO values and lower bandgaps of the molecules offer a higher charge transport in the systems and 5,5″-bis(4-biphenylyl)-2,2′:5′,2″-terthiophene (BP3T) molecule shows the maximum hole and electron mobility, 0.81 cm2 V−1 S−1 and 0.17 cm2 V−1 S−1, respectively. The results have shown that all the title compounds can be fabricated as ambipolar organic semiconductor materials and can be considered for the fabrication of efficient organic light emitting transistors.

Hot carriers perspective on the nature of traps in perovskites

Amongst the many spectacular properties of hybrid lead halide perovskites, their defect tolerance is regarded as the key enabler for a spectrum of high-performance optoelectronic devices that propel perovskites to prominence. However, the plateauing efficiency enhancement of perovskite devices calls into question the extent of this defect tolerance in perovskite systems; an opportunity for perovskite nanocrystals to fill. Through optical spectroscopy and phenomenological modeling based on the Marcus theory of charge transfer, we uncover the detrimental effect of hot carriers trapping in methylammonium lead iodide and bromide nanocrystals. Higher excess energies induce faster carrier trapping rates, ascribed to interactions with shallow traps and ligands, turning these into potent defects. Passivating these traps with the introduction of phosphine oxide ligands can help mitigate hot carrier trapping. Importantly, our findings extend beyond photovoltaics and are relevant for low threshold lasers, light-emitting devices and multi-exciton generation devices.

Theoretical insights on the high and differential charge transfer performance of dithienyl-diketopyrrolopyrrole-based polymers as ambipolar semiconductors

Diketopyrrolopyrrole (DPP)-containing polymers are among the highest mobility semiconductors for field-effect transistor applications. The molecular geometries, electronic structures and charge transport properties as ambipolar organic semiconductors of two series of total 24 donor–acceptor dithienyl-diketopyrrolopyrrole-based oligomers mDTDPPAr and nBDTDPPAr (m = 1–4, n = 1–2, Ar = TT, BT, BDT, TVT) are investigated theoretically through density functional theory and classical Marcus charge transfer theory. The effects of oligomer length form = 1–4, different Ar groups, and different Ar position on the structures and charge transfer properties are systematically studied. It was found that expanding π-conjugate backbone is a viable method to improve their semiconductor performance. Oligomers 4DTDPPTT, 4DTDPPBT, 4DTDPPTVT possess prominent ambipolar semiconductors properties with charge transfer mobilities of 9.62, 10.73, 12.60 cm2 V−1 s−1 for hole and of 7.54, 8.06, 15.56 cm2 V−1 s−1 for electron, respectively. 4DTDPPBDT exhibits large but unbalanced ambipolar performance with hole/electron transfer mobilities of 10.86/20.17 cm2 V−1 s−1 due to the special conjugation of BDT. Changing the order and position of donor and acceptor units has less significant influence on charge transfer mobility. Anisotropic mobilities are also studied to clarify the different charge transfer directions.

Photoexcited hot and cold electron and hole dynamics at FAPbI3 perovskite quantum dots/metal oxide heterojunctions used for stable perovskite quantum dot solar cells

Highly luminescent formamidinium lead iodide (FAPbI3) quantum dots (QDs) exhibit high stability and narrowest bandgap energy among lead halide perovskites, thus they have become one of the most promising materials for the development of perovskite QD-based light-harvesting and near infrared-emitting devices. However, little is known thus far about photoexcited carrier dynamics at the interface between FAPbI3 QDs and charge transport layers, which is very important for both fundamental studies and applications of the QD/charge transport layer heterojunctions. Here, we systematically investigate both hot and cold photoexcited carrier (electron and hole) dynamics including relaxation and transfer at the heterojunction interfaces between FAPbI3 QDs and two kinds of well used charge acceptors, i.e., TiO2 and NiOx. We find that (i) the hot carriers in the FAPbI3 QDs are cooled to cold carriers with a cooling rate in the order of 1011 s−1, and (ii) the cold-electron and -hole injection rates are size dependent and are 2.01–2.29 × 109 s−1 and 1.55–1.96 × 109 s−1 at the two types of FAPbI3 QD/MO (metal oxide) heterojunctions, respectively, which are in good agreements with Marcus theory of charge transfer. In addition, the photoexcited carrier injection efficiency at the two heterojunctions is found to be as high as over 99%, which is the most important key for achieving high photovoltaic performance of the FAPbI3 QD solar cells (QDSCs). Prototypes of the two types of heterojunction-based QDSCs, i.e., normal-structure solar cells based on FAPbI3 QD/TiO2 and inverted-structure solar cells based on FAPbI3 QD/NiOx, were developed and the power conversion efficiencies of more than 9% and 5% were obtained, respectively. Moreover, the photovoltaic performance showed a higher storage stability over 100 days. The photovoltaic performance would be improved largely by optimization of each parts in the QDSCs. Our results shed light on perovskite QD-based optoelectronic devices.

Linkage dependence of charge separated lifetime in small donor-acceptor dyads system

Fast charge separation (CS) process and slow charge recombination (CR) process are critical for effective utilization of solar energy in artificial photosynthesis, photocatalysis and organic photovoltaic devices. Here we demonstrated in a model donor-acceptor (D-A) dyad of styrene based triphenylamine derivative (MTPA) as an electron donor (D), triazine group (TRC) as an electron acceptor (A) (MTPA-TRC) that the CS and CR process can be modulated by the linker groups between donor and acceptor. We synthesized a series of flexibly linked D-A dyads MTPA-TRC-n with different length of methylene units (n = 1, 2, 3, n stands for the number of methylene units) as the spacer and lifetimes of charge-separated states ranging from nanoseconds to milliseconds were observed. According to the Marcus charge transfer theory, MTPA-TRC-n have similar reorganization energies (λ) but decreased electronic coupling matrix element (V). V value is the key factor to dominate the charge transfer rate and charge-separated lifetime in this D-A dyads system. Additionally, the decay coefficient (β) of length dependence of electron transfer rate was decreased from 0.4 Å−1 to 0.3 Å−1 in methanol compared to acetonitrile. It revealed that electronic coupling between the donor and acceptor could be enhanced by the increasing solvent polarity in the non-conjugated linked D-A system.

Optimizing electron-rich arylamine derivatives in thiophene-fused derivatives as π bridge-based hole transporting materials for perovskite solar cells.

Based on the observations of thienothiophene derivatives as π-bridged small molecule hole transporting materials (HTMs), adjusting their electron-rich arylamine derivatives is an effective approach to obtain the alternative HTMs for perovskite solar cells (PSCs). In this work, starting from a new electron-rich arylamine derivative and different π-bridged units of thienothiophene derivatives, a series of arylamine derivative-based HTMs were designed, and their properties were investigated using density functional theory combined with the Marcus charge transfer theory. Compared with the parental Z26 material, the designed H01–H04 exhibit appropriate frontier molecular orbitals, good optical properties, better solubility, good stability and higher hole mobilities. H01–H04 materials with high hole mobility (∼× 10−2) can serve as promising HTMs for improving the efficiency of PSCs. The results confirm that the design strategy of adjusting the electron-rich arylamine derivatives in thienothiophene derivatives as π-bridged HTMs is a reliable approach to obtain the promising HTMs for PSC applications.

π-Bridge modification of thiazole-bridged DPP polymers for high performance near-IR OSCs.

Thiophene-bridged and thiazole-bridged diketopyrrolopyrrole (DPP) polymers for near-infrared (near-IR) photovoltaic applications have been investigated via density functional theory (DFT) and Marcus charge transfer theory. Compared with thiophene-bridged DPP polymers, thiazole-bridged polymers have higher ionization potentials (IPs) but poorer optical absorption and worse charge transport capability. Different beneficial substituents replaced the hydrogen atoms (H) on the thiazole rings for the sake of reversing the disadvantages of thiazole-bridged DPP polymers and making these compounds better near-infrared absorbing materials. In order to gain deep insight into the impact of π-bridge modification on the photoelectronic properties of DPP polymers, their electronic structures, absorption capabilities, intramolecular charge transfer properties and charge transport performances have been analyzed. The calculated results reveal that π-bridge modification is a feasible way to improve the light-absorbing capability, electron excitation properties and charge transport performance of thiazole-bridged DPP polymers. It is expected that π-bridge modification can also work for other polymers containing π-bridge units. We hope that our research efforts will be helpful in the designing of new near-IR absorbing materials and could motivate further improvement of organic solar cells.

Theoretical insights into the 1D-charge transport properties in a series of hexaazatrinaphthylene-based discotic molecules.

Discotic liquid crystal (DLC) materials have attracted considerable attention mainly due to their high charge carrier mobilities in quasi-one-dimensional columns. In this article, five hexaazatrinaphthylene-based DLC molecules were investigated theoretically, and their frontier molecular orbital energy levels, crystal structures, and electron/hole drift mobilities were calculated by combination of density functional theory (DFT) and semiclassical Marcus charge transfer theory. The systems studied in this work include three experimentally reported molecules (1, 2, and 3) and two theoretically designed molecules (4 and 5). Compared with the 1-3 compounds, 4 and 5 have three more extended benzene rings in the π-conjugated core. The present results show that the orders of the frontier molecular orbital energy levels and electron drift mobilities agree very well with the experiment. For 4 and 5, the electron/hole reorganization energies are lower than those of compounds 1-3. Furthermore, the calculated electron/hole transfer integral of 5 is the largest among all the five systems, leading to the highest electron and hole mobilities. In addition, the hydrophobicity and solubility were also evaluated by DFT, indicating that compound 5 has good hydrophobicity and good solubility in trichloromethane. As a result, it is expected that compound 5 can be a potential charge transport material in electronic and optoelectronic devices. © 2017 Wiley Periodicals, Inc.

Density Functional Theory Studies of Hole Mobility in Picene and Pentacene Crystals

We have investigated the electronic properties and hole mobilities of picene and its isomer pentacene using the density functional theory and classical Marcus charge transfer theory. In pristine crystal with herringbone structure, pentacene and picene have drift hole mobilities of 2.147 and 0.644 cm2 V–1 s–1, respectively, which are consistent with recent experimental results. We also show that picene crystal can exhibit maximum mobility up to 2.629 cm2 V–1 s–1 along the π–π stacking direction, while the highest mobility of pentacene crystal exhibits along the herringbone stacking direction. Also the anisotropy of the mobility in the ab plane is 2.4 and 5.6 for picene and pentacene crystals, respectively. Since the air stability of picene is better than pentacene due to lower HOMO levels in picene, we suggest that picene and its homologous phenacenes series are promising candidates toward high mobility organic semiconductor devices with good air stability. This work also sheds light on the favorable or un...

Ultrafast Charge Transfer from CdSe Quantum Dots to p-Type NiO: Hole Injection vs Hole Trapping

Semiconductor quantum dot (QD) to metal oxide electron injection dynamics is well documented in the scientific literature. In contrast to that, not much is known so far about hole injection time scales in such systems. The current study fills this gap. We investigate photocathodes consisting of CdSe QDs and p-type NiO to study hole injection dynamics from the valence band of the QDs to NiO. The combination of two complementary techniques, ultrafast time-resolved absorption and fluorescence spectroscopies, enabled us to distinguish between hole trapping and injection. A kinetic component on the time scale of a few hundreds of picoseconds was identified as hole injection. By changing the size of the QDs, the driving force of the hole injection was tuned and we demonstrated that the hole injection rates are well described by the Marcus theory of charge transfer. In order to enhance the overall hole injection efficiency, we have passivated the CdSe QDs by a gradient ZnS shell. The core–shell QDs show signific...

Charge transfer kinetics at the solid–solid interface in porous electrodes

Interfacial charge transfer is widely assumed to obey the Butler-Volmer kinetics. For certain liquid-solid interfaces, the Marcus-Hush-Chidsey theory is more accurate and predictive, but it has not been applied to porous electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler-Volmer equation but fit the Marcus-Hush-Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The kinetics are thus limited by electron transfer at the solid-solid (carbon-Li(x)FePO4) interface rather than by ion transfer at the liquid-solid interface, as previously assumed. The proposed experimental method generalizes Chidsey's method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus kinetics in modelling batteries and other electrochemical systems.

The reorganization energy of intermolecular hole hopping between dyes anchored to surfaces

We measured the rate of hole hopping between dye molecules on titanium dioxide nanocrystals using cyclic voltammetry. Dyes commonly used in the field of dye sensitized solar cells exhibited efficient intermolecular charge transport, showing apparent diffusion coefficient values between 10−8 up to over 10−7 cm2 s−1 at room temperature. From temperature dependent measurements, we observed that hole transport across dye monolayers is a thermally activated process with Arrhenius activation energies between about 170 and 370 meV depending on the dye. Analysis of the data in terms of non-adiabatic Marcus theory of charge transfer enabled the estimation of the reorganization energy (740–1540 meV) and of an effective electronic coupling for the different systems. The measured reorganization energies show reasonable agreement with values obtained from density functional theory based calculations, validating our computational approach. Finally, we interpret the experimental and calculated data with reference to the chemical structure of the dyes and to the packing of the dyes on the surface of the TiO2 and suggest that delocalization of the HOMO and rigidity of the conjugated molecular structure result respectively in lower outer and inner sphere reorganization energies.