On the Largest Possible Mobility of Molecular Semiconductors and How to Achieve It

Abstract

We use a large database of known molecular semiconductors to define a plausible physical limit to the charge carrier mobility achievable within this materials class, and a clear path toward this limit. From a detailed study of the desirable properties in a large dataset, it is possible to establish whether such properties can be optimized independently and what would be a reasonably achievable optimum for each of them, regardless of the transport mechanism considered. We compute all relevant parameters from a set of almost five thousand known molecular semiconductors, finding that the best known materials are not ideal with respect to all properties. These parameters in decreasing order of importance are realized to be the molecular area, the non-local electron-phonon coupling, the two-dimensional nature of transport, the local electron-phonon coupling and the highest transfer integral. We also find that the key properties related to the charge transport are either uncorrelated or 'constructively' correlated (i.e. they improve together) concluding that a ten-fold increase in mobility is within reach in a statistical sense, on the basis of the available data. We demonstrate that high throughput screenings, when coupled with physical models of transport produce not only specific target materials, as it is done also here, but a more general physical understanding of the materials space and the opportunities of further development.

High-throughput virtual screening for organic electronics: a comparative study of alternative strategies

“…Relying on this strategy and applying the transient localisation theory, which is among the advanced theories that consider all transport parameters on the same footing, the CSD was screened for high mobility materials. 50 The absolute values of calculated mobilities in the framework of TLT are within B35% of experimental data, and the relative values are well reproduced in families of homogenous compounds. 265,288 Furthermore, as shown in a recent study, this theory is also able to reproduce electromechanical responses.…”

“…Another HTVS effort based on the CSD focused on the limit of coherent transport and included the effect of non-local electron phonon coupling. 50 This required the evaluation of the local vibration of molecules embedded in their crystalline environment. Molecular arrangements in the crystal are also needed to study excitonic properties, as illustrated in a recent survey of ∼2200 crystals formed by molecules with bright lowest excited states for which the lowest excitonic band was characterised.…”

A general charge transport picture for organic semiconductors with nonlocal electron-phonon couplings

“…1 g). We note that it is possible to integrate Holstein coupling in the transient localization theory if the intramolecular vibration frequency is much smaller than the transfer integral 33 , 41 , however such scheme is not employed in this work because in most cases ω m is at the same order with V . We believe it is suitable to ascribe the V = 90 meV and Δ V = 40 meV case as TL, because although the TL theory with relaxation time approximation may not correctly produce the correlation function for realistic materials with Holstein coupling, the picture provided by the theory serves as a nice starting point for further analysis.…”

Quantitative Prediction of the Electro‐Mechanical Response in Organic Crystals

“…Charge carrier mobility is evaluated in the framework of the Transient Localization Theory (TLT) developed by Fratini and Ciuchi [ 18,19 ] which has shown a high level of predictive power, [ 17,20,21 ] leading to results in agreement with other theoretical methods [ 22–24 ] at a much lower computational cost. The TLT builds up on the widely accepted evidence [ 25 ] that, in organic materials, the transfer integrals J ij between two neighboring molecules i and j undergo large fluctuations , giving rise to a dynamic disorder which causes a localization of the instantaneous eigenstates of the lattice.…”