First-principles modeling of exciton and charge carrier transport in organic semiconductors is essential tool in studying organic solar cells, light emitting devices, field-effect transistors. Though the theory gives qualitatively correct description of the transport phenomena, the accuracy of the calculated exciton diffusion length or charge carrier mobility is rather uncertain because of a number of uncontrolled approximations made in the course of the modeling. An important contribution to this uncertainty is the choice of the quantum chemistry method. We perform ab-initio, semiempirical, and force field calculations to study the method dependence of the geometry, electronic structure, transfer integrals, and vibronic couplings for 'archetypal' organic semiconductors (oligo-phenylene-vinylene) and representative donors in small-molecule bulk-heterojunction solar cells (based on dithieno-silole, thiadiazolo-pyridine, and thiophene units). Our study shows that for crystalline materials, where the geometry can be provided by the experiment, the main error is in the estimation of the so called spectral overlap: commonly used B3LYP density functional may underestimate it in several times. For amorphous materials the main error is in the geometry: inaccurate geometry produces spurious traps and fast-transfer channels for charge transport.

First-principles modeling of exciton and charge transport in organic semiconductors: Dependence on the quantum chemistry method

244th National Meeting (2012)

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