Abstract
We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic field-effect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves.
Highlights
We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic fieldeffect transistors
This corresponds to a standard modified neglect of diatomic overlap (MNDO)-like linear combination of atomic orbitals (LCAOs) approximation for the construction of charge carriers from basis functions centered at different locations, as implicit in Equation (3), βμν
Visualizations of the spatial charge distribution provide an intuitive understanding of OFET operation and are in agreement with different methods and with experimental and theoretical descriptions of material properties
Summary
Charge transport in organic semiconductors (OSCs) with an amorphous structure is usually described using the concept of hopping-transport. Depending on the amount of disorder in the structure, the concept of band-like transport is discussed as a borderline case in the limit to band structures in well-ordered crystalline systems. For higher temperatures and strong electron-phonon-coupling, the hopping rate or frequency is derived from Marcus theory, for lower temperatures and weak electron-phonon-coupling from the MillerAbrahams model. these approaches can be quite successful, they suffer, for instance, from ambiguities in the definition of the attempt-to-hop rate in the Miller-Abrahams model and the transfer integral in Marcus theory. Some approaches model the transport of only single charge carriers, making it difficult to describe changes in transport characteristics caused by trapping. Multi-agent modeling has become a useful tool for investigating systems consisting of entities with defined or definable characteristics Key to this concept is that the entities act autonomously based on diverging interests and/or different information. We present here a charge-transport model based on a Monte Carlo approach, in which charge carriers are represented by multiple quantum mechanical agents on a local energy hypersurface This model does not require a specific charge-transport mechanism as prerequisite, but rather delivers the mechanism as a result of its application. It is capable of describing the spatial distribution of multiple charge carriers during conduction of electric current in complete devices and covers both static and dynamic disorders by design
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