Development and assessment of novel ultrafast spectroscopy detection methods to characterize excited state electron and energy transfer in molecular electronic devices

This application is for a joint project of the Laboratory of Photochemistry and Spectroscopy at KULeuven and the Laboratory of Quantum Optics at the University of Nova Gorica (Slovenia). Organic photovoltaic cells and organic light emitting diodes consist of thin films of carbon based molecules and convert light into a voltage or vice versa. While their fabrication is cheaper than inorganic devices their efficiency is still much below the theoretical limit. Their improvement requires the knowledge of the yield and rate of formation and decay of intermediate species such as excited states, holes and electrons e.g. by monitoring the light they absorb. As this requires a high concentration of those species and hence a large power density of the laser pulses, artifacts can easily occur. We will develop and test two alternative methods to monitor those species. In a first one a first laser pulse creates an excited state which is ionized by a second pulse, impinging after a chosen time delay. The ejected electrons are collected in function of the time delay and their energy. In the second one the second pulse creates scattered light with a frequency shifted by the vibration frequency of the excited species which is very specific and depends on the bond strengths. These methods can probe the total number of excited species rather than their concentration. They provide direct information on the relevant energy levels in and on the strength of the bonds of the excited species.