Molecular π-conjugated semiconductors are used as active materials enabling charge transport for a variety of applications in organic electronics. However, the lack of long-range order in these amorphous systems hinders the formulation of structure-properties and the systematic improvement of device performances. The use of molecular dynamics (MD) simulations, combined with the estimation (at ab initioor semi-empirical level) of electronic couplings between molecular neighbors, represents a promising strategy to gain insight on the possible charge transport pathways and their dimensionality. In this respect, recent efforts have sought to adapt concepts and algorithms from graph theory and classical resistor theory to define molecular networks made of “electronically connected” units within a bulk amorphous molecular solid. In this representation, every molecule is a node of the graph, and electronic couplings represent the edges connecting the nodes. However, the impact of previous results is limited by the lack of accessibility of the code, no consideration of periodic boundary conditions resulting in finite size effects, and poor computational scaling. In this contribution we present an entirely new implementation and extension of these molecular network concepts. Our code is the first open source software for the analysis of molecular networks, it overcomes the above-mentioned limitations and shows a &gt;100x speedup compared to previously published benchmarks. These improvements have made it possible to extend the original concepts to analyze the dynamical properties of the charge transport networks, such as their lifetime and robustness. As a case study, we consider the impact of alkyl side chain length on the electronic connectivity, thin film morphology and photovoltaic performance of a series of non-fullerene acceptors, derivatives of ITIC. These results can eventually be used to build a macroscopic transport model (ie Kinetic Monte Carlo) including dynamic disorder, similarly to what is being done for crystalline systems.

Charge transport networks in amorphous organic semiconductors

2019 Fall National Meeting

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