Temperature dependence of exciton and charge carrier dynamics in organic thin films

Platt, Andrew; Kendrick, M. J.; Loth, Marsha A.; Anthony, John E.; Ostroverkhova, Oksana

doi:10.1103/physrevb.84.235209

Cited by 53 publications

(111 citation statements)

References 94 publications

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“…2). In the D/A composite films, our previous work 27,47,58 suggests the existence of yet additional channel of charge carrier photogeneration due to dissociation of the CT exciton created by a Coulombically bound hole on the donor molecule and an electron on the acceptor molecule (path 4 in Fig. 2).…”

Section: A Charge Photogenerationmentioning

confidence: 98%

“…2), with relative contribution of each pathway to the overall charge photogeneration being electric field dependent. Since the exact pathway of the CT state formation is unknown, 26,58 we did not impose restrictions on the relative values of c SSC ; c FE , and c CT in Eq. (11).…”

Section: B D/a Compositesmentioning

confidence: 99%

“…In keeping with our previous studies of temperature dependent photocurrents in ADT-TES-F films and their D/A composites, we consider a Poole-Frenkel electric field dependence for these mobilities. 58 Charge carrier trapping effects are incorporated in the model via trapping parameters B p (B n ) for holes (electrons) and total available hole (electron) trap densities of N p (N n ). In ADT-TES-F films, holes are the majority carrier and are assumed to encounter shallower traps than electrons.…”

Section: B Charge Transportmentioning

confidence: 99%

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Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

Johnson

Kendrick

Ostroverkhova

2013

Journal of Applied Physics

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We present a model that describes nanosecond (ns) time-scale photocurrent dynamics in functionalized anthradithiophene (ADT) films and ADT-based donor-acceptor (D/A) composites. By fitting numerically simulated photocurrents to experimental data, we quantify contributions of multiple pathways of charge carrier photogeneration to the photocurrent, as well as extract parameters that characterize charge transport (CT) in organic films including charge carrier mobilities, trap densities, hole trap depth, and trapping and recombination rates. In pristine ADT films, simulations revealed two competing charge photogeneration pathways: fast, occurring on picosecond (ps) or sub-ps time scales with efficiencies below 10%, and slow, which proceeds at the time scale of tens of nanoseconds, with efficiencies of about 11%–12%, at the applied electric fields of 40–80 kV/cm. The relative contribution of these pathways to the photocurrent was electric field dependent, with the contribution of the fast process increasing with applied electric field. However, the total charge photogeneration efficiency was weakly electric field dependent exhibiting values of 14%–20% of the absorbed photons. The remaining 80%–86% of the photoexcitation did not contribute to charge carrier generation at these time scales. In ADT-based D/A composites with 2 wt.% acceptor concentration, an additional pathway of charge photogeneration that proceeds via CT exciton dissociation contributed to the total charge photogeneration. In the composite with the functionalized pentacene (Pn) acceptor, which exhibits strong exciplex emission from a tightly bound D/A CT exciton, the contribution of the CT state to charge generation was small, ∼8%–12% of the total number of photogenerated charge carriers, dependent on the electric field. In contrast, in the composite with PCBM acceptor, the CT state contributed about a half of all photogenerated charge carriers. In both D/A composites, the charge carrier mobilities were reduced and trap densities and average trap depths were increased, as compared to a pristine ADT donor film. A considerably slower recombination of free holes with trapped electrons was found in the composite with the PCBM acceptor, which led to slower decays of the transient photocurrent and considerably higher charge retention, as compared to a pristine ADT donor film and the composite with the functionalized Pn acceptor.

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Section: A Charge Photogenerationmentioning

confidence: 98%

Section: B D/a Compositesmentioning

confidence: 99%

Section: B Charge Transportmentioning

confidence: 99%

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Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

Johnson

Kendrick

Ostroverkhova

2013

Journal of Applied Physics

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“…Spectralon 50 and 100 % reflectance standards from LabSphere, Inc. were used as references with known diffuse reflectance properties. Fluorescence in the vanes was excited with a UV part of solar AM 1.5G radiation (280-400 nm) (solar simulator with AM1.5G filter, dichroic mirror Oriel 81045 and a UV band-pass filter Oriel 81046) and measured in the same geometry as reflectance (Platt et al 2009(Platt et al , 2011Paudel et al 2014). Similar measurements of fluorescence were performed using UV lamp (360-400 nm) and outdoor sunlight with a UV band-pass filter (Oriel 81046) as excitation sources and yielded identical emission spectra.…”

Section: Measurements Of Optical Properties Of Trapsmentioning

confidence: 99%

Visual outdoor response of multiple wild bee species: highly selective stimulation of a single photoreceptor type by sunlight-induced fluorescence

Rao

Ostroverkhova

2015

J Comp Physiol A

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Bees have ultraviolet (UV), blue and green photoreceptor types in their compound eyes with which they locate food sources in landscapes that change continuously in cues emanating from plants and backgrounds against which they are perceived. The complexity of bee vision has been elucidated through studies examining individual species under laboratory conditions. Here, we used a bee-attractive fluorescent blue trap as a model for analyzing visual signals in operation outdoors, and across bee species. We manipulated trap color (appearance to humans under light with weak UV component) and UV-induced fluorescence emission, and aligned field capture results with bee vision models. Our studies show that the bees were attracted to traps that under solar illumination exhibited strong fluorescence emission exclusively in the blue spectral region. Through quantitative analysis, we established that strong spectral overlap of trap emittance with the photosensitivity characteristic of the blue receptor type and minimal overlap with those of the other two receptor types is the most critical property of attractive traps. A parameter has been identified which predicts the degree of attractiveness of the traps and which captures trends in the field data across wild bee species and for a diversity of backgrounds.

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“…For example, by different treatments, the calculated mobility can be either sensitive [7] or insensitive [44] to the dynamic disorder. While some preliminary experimental results appear to not be favorable towards the effect of dynamic disorder [46], further theoretical and experimental studies are certainly needed to clarify its role.…”

Section: Other Theoretical Treatmentsmentioning

confidence: 99%

Charge transport in organic semiconductors: From incoherent to coherent

Yao

Yang

et al. 2013

Chin. Sci. Bull.

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Quantum decoherence in organic charge transport is a complicated but crucial topic. In this paper, several theoretical approaches corresponding to it, from incoherent to coherent, are comprehensively reviewed. We mainly focus on the physical insight provided by each theory and extent of its validity. The aim of this review is to clarify some contentious issues and elaborate on the promising perspectives provided by different approaches. The device model approaches based on both continuous and discretized treatments of the transporting layer will be first discussed. The prominent focus of this review will be devoted to the dynamic disorder model and its variants considering that it is the most promising approach to tackle charge transport problems in organic materials. We will also address other theories such as the variational method. As in all other molecular systems, the electronic coherence is an important aspect in the transport in organic semiconductors (OSCs). The phonon spectrum, consisting of both the intra-and inter-molecular ones, covers an extensive regime and makes almost all the theories about coherence inefficient. As opposed to the biomolecular systems in which the regime of interest is where the long-lived coherence exists and is thus typically specific [1], a very wide range of issues for organic semiconductors spanning completely incoherent (classical) to completely coherent (quantum) exist [2,3]. For example, to study the mobility in a given molecular system, one can utilize classical (device model [4] or kinetic Monte Carlo simulation [5]), semiclassical (surface hopping algorithm [6]), mixed quantum classical (dynamic disorder model [7] and Ehrenfest method [8]), and quantum (variational ansatz) theories. The diverse theoretical treatments make the problems obscure for experimentalists and theoreticians alike. In this review, we will briefly introduce each of these approaches and attempt to provide insights related to their applicability. The charge carriers in OSCs are recognized to be (positively or negatively) charged polarons, due to the strong self-trapping effect from lattice distortion and vibration. Polarons could be small or large, depending on the relative scales of intra-and inter-molecular interactions [9]. In a lattice model, these interactions could be described by diagonal and off-diagonal electron-phonon couplings. A typical single-carrier Hamiltonian then should be as follows [10]

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Temperature dependence of exciton and charge carrier dynamics in organic thin films

Cited by 53 publications

References 94 publications

Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

Visual outdoor response of multiple wild bee species: highly selective stimulation of a single photoreceptor type by sunlight-induced fluorescence

Charge transport in organic semiconductors: From incoherent to coherent

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