Sano–Tachiya–Noolandi–Hong versus Onsager modelling of charge photogeneration in organic solids

Falkowski, Karol; Stampor, Waldemar; Grygiel, Piotr; Tomaszewicz, W.

doi:10.1016/j.chemphys.2011.10.032

Cited by 26 publications

(14 citation statements)

References 46 publications

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“…Commonly used models of exciton dissociation, such as the Onsager-Braun model, consider the rate of dissociation k diss electric field dependent, whereas the primary yield of geminate pair formation (n FE ) is typically assumed to be electric field independent; this assumption has been challenged in several studies. [60][61][62] We found that our data are more consistent with an electric field-dependent competition among pathways 1, 2, and, in composites, 4 of charge carrier photogeneration, which suggests field dependent parameters n SSC ; n FE , and n CT . Since the analytical function describing such competition is not known, in order to extract quantitative information about relative contributions of these different charge generation pathways to the photocurrent at various applied electric fields, we used the simplest possible linear model for the electric field dependence of these parameters, specifically…”

Section: Modelsupporting

confidence: 72%

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: Modelsupporting

confidence: 72%

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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“…(7) show that at a = 0.5 -1 nm, e 1 = 6, T eff = 500 K À 1500 K, and F = 10 7 -10 8 V/m the value of f a eq ðaÞ typically lies in the range between 0.6 Â 10 9 and 2 Â 10 10 1/m. Using parameter k a % 0.02 m/s found from the study of the 3D geminate recombination in some organic photoconductors [46], we obtain J 0 (a,t) < k a f a eq ðaÞ < 4 Â 10 8 1/s. Both flux J 0 (a,t) and flux J 0 (b,t) are seen to be far less than the presumed rate of trapping t À1 0 that justifies assumption (i) made above.…”

Section: Kinetics Of the Diffusive Barrier Crossing Of Pretrapped Chamentioning

confidence: 98%

Photogeneration of charge carriers in a weakly disordered π-conjugated polymer at high photon energies of exciting light

Lukin¹

2015

Synthetic Metals

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“…Here, k B is the Boltzmann constant, r 0 -the mean intrapair distance, r c = 187 Å (for a temperature T = 298 K and relative electric permittivity of an organic solid ε r = 3)-the Onsager radius, i.e., the distance at which the Coulombic electron-hole interaction in a pair is equal to the energy of k B T. The symbol P(m, x) stands for the incomplete gamma function of the integral order m. Note that the calculations of the dissociation probability based on Equation (10) are relatively simple, usually yielding satisfactory results in a wide range of electric field strengths. Nevertheless, the Ω(F) can also be determined using the Sano-Tachiya-Noolandi-Hong approximation [26,27], in which, contrary to the Onsager one, the final recombination of carriers proceeds with a finite velocity and on a sphere of a finite radius, but at the expense of fairly sophisticated and tedious mathematical manipulations (examples of calculations comparing both formalisms are given in our previous paper [28]).…”

Section: Resultsmentioning

confidence: 99%

The Quantum Efficiency Roll-Off Effect in Near-Infrared Organic Electroluminescent Devices with Iridium Complexes Emitters

Mróz

Kesarkar²,

Bossi³

et al. 2020

Materials

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The electroluminescence quantum efficiency roll-off in iridium(III)-based complexes, namely Ir(iqbt) 2 (dpm) and Ir(iqbt) 3 (iqbt = 1 (benzo[b]thiophen-2-yl)-isoquinolinate, dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) utilized as near-infrared emitters in organic light emitting diodes with remarkable external quantum efficiencies, up to circa 3%, 1.5% and 1%, are measured and analyzed. With a 5-6 weight% of emitters embedded in a host matrix, the double-layer solution-processed structure as well as analogous three-layer one extended by a hole-conducting film are investigated. The triplet-polaron, the Onsager electron-hole pair dissociation and the triplet-triplet annihilation approaches were used to reproduce the experimental data. The mutual annihilation of triplets in iridium emitters was identified as prevailingly controlling the moderate roll-off, with the interaction between those of iridium emitters and host matrixes found as being less probable. Following the fitting procedure, the relevant rate constant was estimated to be (0.5 − 12) × 10 −12 cm 3 /s, values considered to be rather too high for disordered organic systems, which was assigned to the simplicity of the applied model. A coexistence of some other mechanisms is therefore inferred, ones, however, with a less significant contribution to the overall emission quenching.

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Sano–Tachiya–Noolandi–Hong versus Onsager modelling of charge photogeneration in organic solids

Cited by 26 publications

References 46 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

Photogeneration of charge carriers in a weakly disordered π-conjugated polymer at high photon energies of exciting light

The Quantum Efficiency Roll-Off Effect in Near-Infrared Organic Electroluminescent Devices with Iridium Complexes Emitters

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