Hopping charge transport in amorphous semiconductors with the spatially correlated exponential density of states

Novikov, S. V.

doi:10.1063/1.4973824

Cited by 4 publications

(16 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In general, the exact origin of trap states at any given depth is not known. It is typical for the sub-bandgap DOS profile to appear exponential over a range of energies [9,11,45] although without any clear physical reason. In the case of conjugated polymers, one important source of site energy distribution is conformational disorder due to variation in intrachain torsion and the resulting variations in the extent of π-conjugation along the polymer backbone.…”

Section: Introductionmentioning

confidence: 99%

Relating Chain Conformation to the Density of States and Charge Transport in Conjugated Polymers: The Role of the β -phase in Poly(9,9-dioctylfluorene)

et al. 2019

View full text Add to dashboard Cite

Charge transport in π-conjugated polymers is characterized by a strong degree of disorder in both the energy of conjugated segments and the electronic coupling between adjacent sites. This disorder arises from variations in the structure and conformation of molecular units, as well as the weak intermolecular binding interactions. Although disorder in molecular conformation can be expected to influence the density of states (DOS) distribution-and hence, optoelectronic properties of the material-until now, there has been no direct study of the relationship between a distinct conformational defect and the charge transport properties of a conjugated polymer. Here, we investigate the impact of introducing an extended, planarized chain geometry, known as the "β-phase," on hole transport through otherwise amorphous films of poly(9,9dioctylfluorene) (PFO). We show that while β-phase introduces a striking drop of about a hundredfold in time-of-flight (TOF) hole mobility (μ h ) at room temperature, it reduces the steady-state μ h measured from hole-only devices by a factor of less than about 5. In order to reconcile these observations, we combine high-dynamic-range TOF photocurrent spectroscopy and energy-resolved electrochemical impedance spectroscopy to extract the hole DOS of the conjugated polymer. Both methods show that the effect of the β-phase content is to introduce a sharp sub-bandgap feature into the DOS of glassy PFO lying about 0.3 eV above the highest occupied molecular orbital. The observed energy of the conformational trap is consistent with electronic structure calculations using a tight-binding approach. Using the obtained DOS with a driftdiffusion model capable of resolving charge carriers in both time and energy, we show how the seemingly contradictory transport phenomena obtained via the time-resolved, frequency-resolved, and steady-state methods are reconciled. The results highlight the significance of energetic redistribution of charge carriers in affecting transport behavior. This work demonstrates how charge-carrier mobility in organic semiconductors can be controlled via molecular conformation, and it resolves a long-standing debate over how different (equilibrium versus nonequilibrium) transport techniques reveal electronic properties of disordered solids in a unified manner.

show abstract

Section: Introductionmentioning

confidence: 99%

Relating Chain Conformation to the Density of States and Charge Transport in Conjugated Polymers: The Role of the β -phase in Poly(9,9-dioctylfluorene)

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Nontrivial approximate value of ∆D could be calculated by the saddle point method for κ → 1 in close analogy with the calculation of v in Ref. 22 but, unfortunately, this region is unphysical due to the divergence of Z 4 (x, y, z). It is interesting to note that Eq.…”

Section: A General Considerationmentioning

confidence: 95%

“…A suitable method to introduce spatial correlation in the exponentially distributed random energy landscape has been suggested in Ref. 22. There is a well known representation for the exponentially distributed random variable which employs two auxiliary independent identically distributed random Gaussian variables X and Y having zero mean and unit variance σ 2 = 1.…”

Section: Random Energy U (X)mentioning

confidence: 99%

“…for κ < 1, here and later we consider the simplest case c X (x) = c Y (x) = c(x), possible generalizations may be found in Ref. 22. We assume also that our system is isotropic, so c(x) = c(−x).…”

Section: Random Energy U (X)mentioning

confidence: 99%

“…For the approximately exponential DOS considered in Ref 26. we should expect c U (x) ∝ 1/x 5 and c(x) ∝ 1/x 5/2[22], though parameter U 0 is typically very small and the resulting total DOS in amorphous organic semiconductors is mostly formed by other contributions.…”

mentioning

confidence: 97%

See 2 more Smart Citations

Diffusion of a particle in the spatially correlated exponential random energy landscape: Transition from normal to anomalous diffusion

Novikov

2018

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

Diffusive transport of a particle in a spatially correlated random energy landscape having exponential density of states has been considered. We exactly calculate the diffusivity in the nondispersive quasi-equilibrium transport regime for the 1D transport model and found that for slow decaying correlation functions the diffusivity becomes singular at some particular temperature higher than the temperature of the transition to the true non-equilibrium dispersive transport regime. It means that the diffusion becomes anomalous and does not follow the usual ∝ t law. In such situation, the fully developed non-equilibrium regime emerges in two stages: first, at some temperature there is the transition from the normal to anomalous diffusion, and then at lower temperature the average velocity for the infinite medium goes to zero, thus indicating the development of the true dispersive regime. Validity of the Einstein relation is discussed for the situation where the diffusivity does exist. We provide also some arguments in favor of conservation of the major features of the new transition scenario in higher dimensions.

show abstract

Charge transport in the spatially correlated exponential random energy landscape: effect of the nonpositive correlation function

Novikov

2022

Phys. Chem. Chem. Phys.

Self Cite

View full text Add to dashboard Cite

show abstract

Hopping charge transport in amorphous semiconductors with the spatially correlated exponential density of states

Cited by 4 publications

References 40 publications

Relating Chain Conformation to the Density of States and Charge Transport in Conjugated Polymers: The Role of the β -phase in Poly(9,9-dioctylfluorene)

Relating Chain Conformation to the Density of States and Charge Transport in Conjugated Polymers: The Role of the β -phase in Poly(9,9-dioctylfluorene)

Diffusion of a particle in the spatially correlated exponential random energy landscape: Transition from normal to anomalous diffusion

Charge transport in the spatially correlated exponential random energy landscape: effect of the nonpositive correlation function

Contact Info

Product

Resources

About