Quantitative Femtosecond Charge Transfer Dynamics at Organic/Electrode Interfaces Studied by Core‐Hole Clock Spectroscopy

Abstract

Organic semiconductor materials have important applications in organic electronics and other novel hybrid devices. In these devices, the transport of charge carriers across the interfaces between organic molecules and electrodes plays an important role in determining the device performance. Charge transfer dynamics at the organic/electrode interface usually occurs at the several femtoseconds timescale, and quantitative charge transfer dynamics data can been inferred using synchrotron-based core-hole clock (CHC) spectroscopy. In this research news, we have reviewed recent progress in the applications of CHC spectroscopy on the quantitative characterization of charge transfer dynamics at organic/electrode interfaces. By examining charge transfer dynamics at different types of interface, from weakly interacting van der Waals-type interfaces to interfaces with strong covalent bonds, we discuss a few factors that have been found to affect the charge transfer dynamics. We also review the application of CHC spectroscopy to quantify through-bonds and through-space charge transport in organic molecules.

Ways to Spin Resolved Core-Hole-Clock Measurements

“…the empty conduction band of a solid (Fig. 1b) and 1h final states result [1][2][3][4]. If core decay and charge delocalization occur on similar time scales, the spectrum shows a mixture of both (Fig.…”

“…If core decay and charge delocalization occur on similar time scales, the spectrum shows a mixture of both (Fig. 1b) [1][2][3][4]. Apart from a reduced spectator shift by different extra-atomic screening of the 2h and the effective one hole states ( Fig.…”

“…The core-hole-clock (CHC) method is an approach to measure delocalization times of electrons utilizing the lifetime of inner-shell vacancies-the core holes-as an internal time standard [1][2][3][4]. It has been used for investigations of charge transfer times from adsorbates to their substrates, e.g.…”

“…It has been used for investigations of charge transfer times from adsorbates to their substrates, e.g. for physisorbates on metals [5][6][7] and semiconductors [8], but also for chemisorbates on metals [1][2][3][4][9][10][11][12], including strongly chemisorbed radicals with charge transfer times in the sub-femtosecond range [10][11][12]. It was also used to determine charge transit times through thin dielectric layers [13] and through monolayers of graphene on different substrates [14], and it was extensively applied in studies of charge transport dynamics in hybrid systems containing larger organic molecules [3,4,15].…”

“…For many systems the 1h and 2h1e, and the 2h contributions to the combined spectrum-often labeled as "coherent" and "incoherent" contributions, because the coherence of the wave function is lost upon charge transfer-can be untangled, either because the spectator shift is large enough, or because parts with constant kinetic or constant binding energy can be discerned. With the intensities I of the different contributions to the decay spectrum and the known lifetime of the core hole τ core [28,29], the charge transfer time τ ct can be calculated [1][2][3][4]:…”