We develop a general computational procedure to compute the photoexcited electronic mobility in semiconductor slabs using a combined density matrix theory and electronic band structure treatment. This method has been applied to 6x4 Si(111):H slabs for varying thickness (from 4-12 layers) both with and with out adsorbed silver clusters. Electronic band states were generated for 10 k-points in the Γ→Χ direction in an orthorhombic supercell using density functional theory in a plane wave basis using PBE exchange and correlation density functionals. Steady state reduced density matrix methods including dissipative effects were used to compute the photoexcited populations of each electronic band in response to the absorption of photons in the visible and near visible range. We find that the absorption of small silver clusters to the surface of the Si(111) slab enhances photoexcited electronic mobility by limiting the recombination of photoexcited electrons and holes. With increasing slab thickness this effect is reduced as the states contributed to the bandgap by the silver cluster become delocalized into the silicon slab. Increasing the size of the silver cluster on the thicker slabs appears to restore the effect photoexcited electronic mobility seen in the smaller slabs. This effect is important in the development of future photovoltaic materials where photoexcited electronic populations and photoexcited electronic mobilities both affect the efficiency of conversion of light into electrical energy.

Modeling the effect of varying surface thickness on the photomobilities of Si slabs

251st National Meeting (2016)

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