Quantitative femtosecond charge transfer dynamics at organic/electrode interfaces studied by core-hole clock spectroscopy

Organic semiconductors have important applications in organic electronics and other novel hybrid devices. The transport of charge carriers across the interfaces between organic molecules and electrodes plays an important role in determining the device performance.

Understanding the charge transfer dynamics and quantifying the relevant timescale at relevant organic/electrode interfaces, which are intimately linked to the device performance and functionalities, provide fundamental insights into the electronic processes in organic molecules and their interfaces. They also serve as an important gauge for the rationale design and engineering of organic interfaces at the molecular scale. Charge transfer dynamics at these interfaces usually occurs at the several femtoseconds timescale which presents tremendous challenges to conventional pump-probe based time-resolved techniques.

Synchrotron-based core-hole clock (CHC) spectroscopy, which uses the intrinsic core-hole lifetime of a few fs as an internal reference clock to time charge transfer dynamic processes, provides sub-fs temporal information on charge transfer processes with elemental and orbital specificity. We have used the CHC technique to quantitatively study charge transfer dynamics in several model organic/electrode systems. Combined with other soft x-ray spectroscopies, it enables us to identify critical factors affecting the charge transfer dynamics at organic/electrode interfaces.