Charge Transport in Molecular Materials: An Assessment of Computational Methods

Oberhofer, Harald; Reuter, Karsten; Blumberger, Jochen

doi:10.1021/acs.chemrev.7b00086

Cited by 355 publications

(446 citation statements)

References 386 publications

(939 reference statements)

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“…Their scattering rate decreases monotonically with phonon energy (and thus with mode number, since the modes are numbered in order of increasing energy). Similar to simple metals and nonpolar inorganic semiconductors, the main source of scattering is acoustic modes, with smaller contributions from other molecular rigid vibrations and librations (modes [4][5][6][7][8][9][10][11][12]. This result is further illustrated in Fig.…”

Section: Resultsmentioning

confidence: 92%

“…3(b) for selected intramolecular phonons. Note that the intermolecular phonons have either zero or very small minimum frequency since they correspond to transverse acoustic (TA) and longitudinal acoustic (LA) vibrations (modes 1-3) or other rigid vibrations or librations of the molecules (modes [4][5][6][7][8][9][10][11][12]. By contrast, the intramolecular modes 20-90 in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

et al. 2018

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Predicting charge transport in organic molecular crystals is notoriously challenging. Carrier mobility calculations in organic semiconductors are dominated by quantum chemistry methods based on charge hopping, which are laborious and only moderately accurate. We compute from first principles the electron-phonon scattering and the phonon-limited hole mobility of naphthalene crystal in the framework of ab initio band theory. Our calculations combine GW electronic bandstructures, ab initio electron-phonon scattering, and the Boltzmann transport equation. The calculated hole mobility is in very good agreement with experiment between 100-300 K, and we can predict its temperature dependence with high accuracy. We show that scattering between intermolecular phonons and holes regulates the mobility, though intramolecular phonons possess the strongest coupling with holes. We revisit the common belief that only rigid molecular motions affect carrier dynamics in organic molecular crystals. Our paper provides a quantitative and rigorous framework to compute charge transport in organic crystals and is a first step toward reconciling band theory and carrier hopping computational methods.

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Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

et al. 2018

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“…IP is an important parameter of a donor molecule as it is associated with the energy of HOMO which in turn correlates with the donor valence band edge energies and the V OC . [25] It has already been used in previous highthroughput virtual screening for high carrier mobility in organic semiconductors. A large polarizability of organic molecules is expected to reduce the exciton binding energy by stabilizing the charge separated states.…”

Section: Descriptors For Machine Learning Modelsmentioning

confidence: 99%

“…[23,24] Therefore, the accurate simulating of OPVs requires high-level theoretical methods in quantum chemistry, quantum dynamics and statistical mechanics, and in recent years there have been substantial progress for the theoretical understanding of many microscopic processes such as charge transport, [25] exciton dissociation, [26,27] singlet fission, [28][29][30] etc. [23,24] Therefore, the accurate simulating of OPVs requires high-level theoretical methods in quantum chemistry, quantum dynamics and statistical mechanics, and in recent years there have been substantial progress for the theoretical understanding of many microscopic processes such as charge transport, [25] exciton dissociation, [26,27] singlet fission, [28][29][30] etc.…”

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confidence: 99%

Toward Predicting Efficiency of Organic Solar Cells via Machine Learning and Improved Descriptors

Sahu

Rao

Troisi

et al. 2018

Advanced Energy Materials

196

220

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include the strong electron-electron interactions and strong electron-phonon couplings as well as the complicated donor/ acceptor (D/A) interface morphology, which are fundamentally different from inorganic semiconductors. [23,24] Therefore, the accurate simulating of OPVs requires high-level theoretical methods in quantum chemistry, quantum dynamics and statistical mechanics, and in recent years there have been substantial progress for the theoretical understanding of many microscopic processes such as charge transport, [25] exciton dissociation, [26,27] singlet fission, [28][29][30] etc. These methods are useful for few benchmark systems but cannot be used to explore the chemical space, i.e., screen a large number of candidate materials.The predictive power of a theoretical model by high-throughput virtual screening has been explored in the recent years. [31][32][33][34][35][36][37][38][39][40] For example, in the Harvard Clean Energy Project (CEP), [41] Aspuru-Guzik and co-workers have screened ≈2.3 million compounds by employing the Scharber model [42,43] to find out efficient new donor molecules for OPVs. Here, the computed energies of the highest occupied molecular orbital (HOMO)/the lowest unoccupied molecular orbital (LUMO) of organic molecules are calibrated to experimentally determined values, and then employing an averaging scheme, energies of HOMO/LUMO are estimated to use them as input in the Scharber model. However, the prediction of PCE of an OPV is much more challenging compared to the energies of orbitals. Very recently, the same research team [44] noticed that the Scharber model, widely used in these virtual screening works, is not accurate enough for the prediction of PCE, and calibration of PCE by considering molecular similarity, molecular weight and band gap energy leads to improvement in correlation between experimental (49 OPVs) and calculated PCE (Pearson's coefficient (r) is increased from 0.30 to 0.43). Further, the Scharber model is only optimized for the PC 61 BM acceptor [42] and a more general model is desired to take account of nonfullerene molecules.In an OPV, energy conversion is accomplished by four consecutive steps: i) absorption of photons and exciton formation, ii) exciton diffusion to D/A interface, iii) exciton dissociation, and iv) transport of holes/electrons to the respective electrode. Taking account of all these processes, the efficiency of a device depends on many microscopic properties of the organic material such as optical gap, charge-carrier mobility, ionization To design efficient materials for organic photovoltaics (OPVs), it is essential to identify the largest number of parameters that control their properties and build a model using these parameters (known as descriptors) for the prediction of the power conversion efficiency (PCE). By constructing a dataset for 280 small molecule OPV systems, it is found that for all high-performing devices, frontier molecular orbitals of donor molecules are nearly degenerated and in such cases, orbitals other than just high...

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“…The rate of electron transfer is described in the framework of the Fermi's Golden Rule; assuming the Franck-Condon www.advmatinterfaces.de approximation and the high-temperature regime (when the vibrational modes can be treated classically), the charge-transfer rate is given by the semiclassical Marcus expression [34][35][36][37][38] …”

Section: Charge-transfer Parametersmentioning

confidence: 99%

Structure and Charge Transport Properties of Cycloparaphenylene Monolayers on Graphite

Pérez-Guardiola

Pérez-Jiménez

Muccioli³

et al. 2019

Adv Materials Inter

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The synthesis of CPPs has been experimentally challenging due to the strain energy needed to close the ring. [7] Vögtle and co-workers [8,9] attempted to synthesize CPPs from macrocycles formed by arene and cyclohexane units to therefore reduce the strain energy of the system. However, the first synthesis of CPPs was afforded only by Jasti et al. [10] in 2008, followed by the first selective synthesis of CPPs by Itami and co-workers [11,12] using a modular approach to build [n]CPPs with n ⩾ 12. Other successfully strategies (Yamago et al. [13] ) use a square-shaped tetra platinum biphenyl complex as an intermediate to selectively synthesize the [8]CPP molecule. In the above mentioned works, it was possible to obtain CPPs in the milligram-scale, with Jasti and co-workers [6,14] producing the first gram-scale synthesis. The smallest CPP synthesized up to date is [5]CPP, [15] which shows the great success achieved so far in overcoming the strain energy.Concerning the supramolecular packing, the solid-state (3D) structure of CPPs has been characterized in several works by means of X-ray diffraction. [16,17] The molecules self-assemble in a herringbone (HB) pattern independently of their size, as it often happens for other π-conjugated systems. An exception is the [6]CPP case, for which three different polymorphs have been found up to date. The first solid-state characterization of [6]CPP revealed a tubular-like structure, [14] but a recent study revealed that the crystallographic structure might depend on the crystallization conditions, also finding a herringbone configuration a few kcal mol −1 more stable than the tubular one. [18] More recently, another polymorph of [6]CPP has been found when the crystallization is carried out by sublimation at 220 °C. In these conditions, no solvent molecules are occluded inside the [6]CPP cavity, and thus, a concave-convex structure appears (i.e., molecules tightly packed in a T-like shape minimizing the internal space inside the cavities). [19] These findings clearly reveal the subtle yet dominant effect of the weak intermolecular interactions driving the supra molecular self-assembly of these systems. Motivated by this, some of us investigated in a previous theoretical work the adsorption energies of [8]CPP on small carbon nanoflakes (circumcirmcumcoronene) and how these through-space weak forces can serve to immobilize the systems in energetically favored configuration. [20] In the present study, we wish to go a step further and employ a tailored force field and molecular dynamics (MD) simulations to predict the supramolecular structure of thin films of CPPs on graphite surfaces. The systematic exploration of the adsorption The nanoscale organization of cycloparaphenylene molecules when physisorbed on a graphite surface is theoretically investigated by means of atomistic molecular dynamics simulations employing a tailored and benchmarked force field. The landing of a single molecule is first considered, to progressively deposit more molecules to finally reach the full coverage...

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Charge Transport in Molecular Materials: An Assessment of Computational Methods

Cited by 355 publications

References 386 publications

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

Charge transport in organic molecular semiconductors from first principles: The bandlike hole mobility in a naphthalene crystal

Toward Predicting Efficiency of Organic Solar Cells via Machine Learning and Improved Descriptors

Structure and Charge Transport Properties of Cycloparaphenylene Monolayers on Graphite

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