Fractional and Integer Charge Transfer at Semiconductor/Organic Interfaces: The Role of Hybridization and Metallicity

Erker, Simon; Hofmann, Oliver

doi:10.1021/acs.jpclett.8b03857

Cited by 17 publications

(17 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the dilute case, the LUMO is partially occupied by 0.3 e , whereas the partially occupied LUMO orbitals of the two nonequivalent molecules in the densely packed case are not equally charged, i.e., we find that one molecule presents a partial occupation of 0.25 e on its partially filled LUMO and the other 0.1 e . The fractional charge transfer observed here (including the disproportional CT for two molecules in the unit cell) obtained with a range‐separated hybrid functional, in contrast to the experimental evidence of integer charge transfer, is likely a consequence of the remaining electron delocalization error present in this functional, allied to the need of much larger supercells that are not computationally feasible to simulate integer CT. [ 30,31 ] With this static description (i.e., without temperature‐induced effects from nuclear motion) of the vdW heterostructure we obtain adequate qualitative agreement between experiment and theory. In the following, we continue by including quantum zero‐point motion and temperature‐dependent effects in our calculations.…”

Section: Resultsmentioning

confidence: 65%

Temperature‐Dependent Electronic Ground‐State Charge Transfer in van der Waals Heterostructures

et al. 2021

View full text Add to dashboard Cite

A single layer of a 2D material may be insulating (e.g., hexagonal boron nitride), semiconducting (e.g., MoS 2 ), or conducting (e.g., graphene), and thus all electrical material properties required for the construction of an electronic or optoelectronic device are available in the monolayer limit. [3][4][5][6] Stacks of such mono layers are typically bound by weak van der Waals (vdW) interlayer interactions, and vdW heterostructures have emerged as prime candidates for realizing electronic and optoelectronic functions in the smallest possible volume. The type and efficiency of the functionality that can be achieved depends critically on the electronic energy level alignment across the heterostructure, [7] and substantial charge density rearrangement upon contact can occur, depending on the electronic structure of each component. Consequently, charge rearrangement and also charge transfer (CT) phenomena that define the electronic ground state of vdW heterostructures must be thoroughly understood Electronic charge rearrangement between components of a heterostructure is the fundamental principle to reach the electronic ground state. It is acknowledged that the density of state distribution of the components governs the amount of charge transfer, but a notable dependence on temperature is not yet considered, particularly for weakly interacting systems. Here, it is experimentally observed that the amount of ground-state charge transfer in a van der Waals heterostructure formed by monolayer MoS 2 sandwiched between graphite and a molecular electron acceptor layer increases by a factor of 3 when going from 7 K to room temperature. State-of-the-art electronic structure calculations of the full heterostructure that accounts for nuclear thermal fluctuations reveal intracomponent electron-phonon coupling and intercomponent electronic coupling as the key factors determining the amount of charge transfer. This conclusion is rationalized by a model applicable to multicomponent van der Waals heterostructures.

show abstract

Section: Resultsmentioning

confidence: 65%

Temperature‐Dependent Electronic Ground‐State Charge Transfer in van der Waals Heterostructures

et al. 2021

View full text Add to dashboard Cite

show abstract

“…There, FCT due to the bonding of the CN groups to the Zn atoms at the surface (affecting all molecules in Figure 12d) coexists with ICT into the π-system of only a fraction of the adsorbed molecules (molecule 1 in Figure 12d). [251] Whether charge transfer occurs at all for a specific material combination, again depends on the adiabatic ionization energies or electron affinities of the adsorbate layer, but also on the structure and density of the molecular overlayer, as well as on the thickness of the dielectric layer. [250] Whether the charge localizes or not (i.e., whether FCT or ICT occurs) depends on the degree of hybridization and the strength of the lattice relaxation.…”

Section: The Integer Charge-transfer (Ict) Situationmentioning

confidence: 99%

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

Zojer

Taucher

Hofmann

2019

Adv Materials Inter

Self Cite

138

168

View full text Add to dashboard Cite

The presence of dipolar layers determines the functionality of most technologically relevant interfaces. The present contribution reviews how periodic dipole assemblies modify the properties of such interfaces through so‐called collective electrostatic effects. They impact the ionization energies and electron affinities of thin films, change the work function of metallic and semiconducting substrates, and determine the alignment of electronic states at interfaces. Dipolar layers originate either from the assembly of polar molecules or they arise from interfacial charge rearrangements triggered by the deposition of an adsorbate layer. Such charge rearrangements result from the omnipresent Pauli pushback caused by exchange interaction, from covalent bonds, or from charge transfer following the deposition of particularly electron rich (donors) or electron poor molecules (acceptors). A peculiarity of charge‐transfer interfaces is that they enter the realm of Fermi‐level pinning, where the sample work function becomes independent of the substrate and is solely determined by the electronic properties of the adsorbate. Beyond changing work functions and injection barriers, the presence of polar layers also modifies various other physical observables, like core‐level binding energies or tunneling currents in monolayer junctions. All these aspects suggest that polar layers can also be exploited for electrostatically designing the electronic properties of materials.

show abstract

“…An example is an integer charge transfer model whereby the addition of strongly electron donating n-type (reducing agent) or strongly electron withdrawing p-type (oxidising) molecule can inject or withdraw electrons respectively from the host material. [130][131][132][133] Modelling a p-type dopant as an oxidising agent, it can be employed to a semiconductor to remove an electron from the highest occupied molecular orbital (HOMO) of the host material. Consequently, this would introduce some quantity of positively charged species (holes) across the conjugated backbone in the polymer.…”

Section: Doping In Organic Semiconductorsmentioning

confidence: 99%

“…Other models such as hybrid charge integer have been posited as being more comprehensive. 131,[142][143][144] The hybrid charge transfer model explains doping of conducting molecules through the formation of charge transfer states induced from orbital mixing between donor and acceptor orbitals. This accounts for when the dopant remains in the materials (post doping).…”

Section: Doping In Organic Semiconductorsmentioning

confidence: 99%

“…This hybrid charger transfer model can be used to explore charged counter ions and anions to the charged transfer states which the dopant itself may act as a stabilizer. 131 Other doping strategies may include the imbedding of conductive nanomaterials within the polymer matrix. 145,146 This approach would take the unique electronic qualities of the guest material into account and therefore by tuning the concentration of the guest material relative to the host matrix, it is possible to improve the Seebeck coefficient for example.…”

Section: Doping In Organic Semiconductorsmentioning

confidence: 99%

See 1 more Smart Citation

Improvement to the thermoelectric properties of PEDOT:PSS

Atoyo¹

View full text Add to dashboard Cite

Thermoelectric materials can convert waste heat to electricity without moving parts. Extensive research into improving the efficiency of inorganic thermoelectric materials has allowed some materials such as bismuth tellurides to be commercialized. These materials, however, contain materials in low abundance on earth such as tellurium therefore their use and scaled production would be limited. Organic and hybrid thermoelectric materials can meet the gap for niche markets as well as be synthesized on mass, due to utilization of earth abundant elements such as carbon, sulphur, and nitrogen. The thermoelectric generators require several n and p-type materials connected for optimal efficiency. There are many ways to create inorganic thermoelectric n and p-types. However, for the organic thermoelectric materials the efficiency lags because of their lower electrical conductivity and Seebeck coefficient as well as the lack of effective strategies in the development of n-type materials. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most successful and researched p-type organic thermoelectric material and thus, the thesis will explore effective strategies for decoupling the apparent trade-offs observed when improving either the electrical conductivity or Seebeck coefficient. The first major contribution to knowledge discussed in this study is the utilization of a reducing agent treatment on PEDOT-ionic liquid composites (reader is advised to refer to chapter 5). Another significant finding was the successful development of a novel route to an n-type single walled carbon nanotube, PEDOT:PSS composite (please refer to chapter 6). The final and most significant contribution to knowledge in this research project was the development of a set of novel single walled carbon nanotube, ionic liquid, PEDOT:PSS composites whereby after a post treatment with a guanidinium iodide in ethylene glycol solution allowed for improvement of the electrical conductivity from 3.4 S cm -1 to 3665 S cm-1 and Seebeck coefficient from 12 μV K-1 to 27 μV K-1 thereby leading to an optimised power factor of 236 μW m-1 K-1 at 140 °C (please refer to chapter 7).

show abstract

Fractional and Integer Charge Transfer at Semiconductor/Organic Interfaces: The Role of Hybridization and Metallicity

Cited by 17 publications

References 56 publications

Temperature‐Dependent Electronic Ground‐State Charge Transfer in van der Waals Heterostructures

Temperature‐Dependent Electronic Ground‐State Charge Transfer in van der Waals Heterostructures

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

Improvement to the thermoelectric properties of PEDOT:PSS

Contact Info

Product

Resources

About