We use pump-probe spectroscopies to characterize the exciton dynamics in organic semiconductors and hybrid organic-inorganic heterojunctions. Organic semiconductors combine the electronic properties of traditional semiconductors with the mechanical flexibility and chemical tunability of molecular precursors. These materials already demonstrated their relevance in prototypical optoelectronic devices such as light-emitting diodes (LEDs) and photovoltaic cells, but a more complete understanding of the mechanisms governing charge generation, transport, and recombination in these materials is critical for improving their efficiency and unlocking new functionalities. Studying these systems at the microscopic level allow us to uncover how energy levels align at donor-acceptor interfaces, how excitons are separated into free carriers, and how we can modify the molecular film in order to gain control over the heterojunction electronic properties.
In our laboratory, we exploit a pulsed laser and synchrotron radiation to perform time-resolved X-ray spectroscopies in the sub-nanosecond time scale. Compared to conventional laser-based spectroscopies, X-rays allow accessing the core levels of the system, which enables element-selective tracking of the excited state dynamics. This advantage can provide crucial insights in complex heterojunctions, which can help disentangle the contribution of the different materials to the charge transfer mechanisms.