Dresden 2020 – scientific programme

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DS: Fachverband Dünne Schichten

DS 30: Poster: Organic Thin Films and Thin Oxides

DS 30.2: Poster

Wednesday, March 18, 2020, 15:00–18:00, P1A

Exploring charge transfer in a Protoporphyrin IX - Semiconductor Model System — •Ken Lim, Felix Eckmann, and Martin Stutzmann — Walter Schottky Institut, Technische Universität München, 85748, Garching, Germany

Photocatalytic reduction of CO₂ into carbon neutral solar fuels that can be easily stored are to date typically achieved by either homogeneous (in solution) or heterogeneous (on metal and semiconductors) catalysis techniques. This work investigates a simple model system of semiconductor substrates covered with Protoporphyrin IX (PPIX) monolayers in order to explore the possibility of combining heterogeneous and homogeneous catalysis approaches, benefiting from the advantages of both. To that end, PPIX monolayers were deposited onto various semiconductor substrates via the Langmuir-Blodgett process. Monolayer morphology was studied using atomic force microscopy revealing closely packed molecules on the surface with a tilted orientation. Fluorescence spectroscopy was used to evaluate the model system whereby quenching of monolayer fluorescence due to charge transport to the substrate suggests a decrease in efficiency for a photo-catalytically reducing device. Our data shows a dependence of fluorescence peak position and intensity on the excitation wavelength and underlying substrate, especially when exciting at the Soret Band for AlN and GaN. Additionally, experiments with AlGaN substrates demonstrate a positive correlation between substrate bandgap and PL intensity, indicating fluorescence quenching due to electron transfer between excited S2 states and conduction band of the semiconductor.