Effect of site energy fluctuation on charge transport in disordered organic molecules

What is it about?

In this work, we explore the structural dynamics and its correlated effect on charge transport in organic semiconductors with the aid of electronic structure calculations, molecular dynamics, and kinetic Monte-Carlo simulations. In this paper, we have proposed the differential entropy dependent charge density and diffusion equations to explore the physics of deviation in original Einstein relation (via ideality factor) for disordered solids. In addition, we have modeled the momentum-energy redistribution functions to analysis the drift-diffusion transport in molecular semiconducting devices.

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Why is it important?

Key Observation: The present study clearly shows the dynamic to static disorder conversion mechanism when the value of site energy difference increases. Main implication of this study on device performance is that the applied field (or bias condition) enhances the charge transport for dynamical system of a few stacked units only (or limited hopping sites). But, at zero bias (or zero electric field), the self-diffusion (or trap-free diffusion) is the primary mechanism for charge transport in extended hopping systems. Our theoretical study concludes three important corollaries are as follows, (1) The Langevin transport is anticipated for zero (or small) energy disordered dynamical systems, and Shockley-Read-Hall charge transport is expected in the large energy disordered systems. (2) With bias conditions, a significant loss in charge transfer rate is observed at each hopping site of the dynamical system of extended units, which leads to incoherent transport. (3) On the other hand, at zero bias, the self-diffusion transport (rather than drift-diffusion) is occurred and it dominantly follows the coherent mixed hopping transport due to negligible dispersion.

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