Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 34: Poster: Surface Dynamics & Electron-Driven Processes

O 34.6: Poster

Tuesday, March 19, 2024, 18:00–20:00, Poster C

Defect assisted charge transfer across silicon-related heterojunctions — •Marvin Krenz, Wolf Gero Schmidt, and Uwe Gerstmann — Paderborn University, Warburger Str. 100, 33098 Paderborn

Charge transfer is highly relevant for many physical, chemical, and biological processes. The transfer of triplet excitons across the tetracene (Tc)-silicon interface in sensitized solar cells is a recent example. Another one is the active a-Si:H/c-Si interface of silicon-based solar cells. In both cases, the presence of dangling bond (db) defects are often considered detrimental to material performance. While the atomistic details of the interfaces are decisive for maximizing the charge transfer, the transfer mechanism and related dynamics are essentially unknown.

Here, we present ab initio molecular dynamics calculations that provide a microscopic understanding of the charge and exciton transfers across the above mentioned interfaces. The related electron hopping at level crossings in the band structure of the 2D periodic structures is described by c-DFT based surface hopping algorithms [1]. The transfer characteristics are found to depend in fact strongly on the presence of Si dangling bonds at the interfaces. At the Tc-Si(111):H interface they are even required to enable the excitation transfer. Defect induced states close to the valence band directly assist the hole transfer into Si bulk, and the exciton's electron is found to follow the hole within a few femtoseconds.

[1] M. Krenz, U. Gerstmann, W.G. Schmidt, ACS Omega 5, 24057 (2020).

Keywords: MD simulations; charge transfer; heterojuntions; surface hopping; defects