I am working on transport properties of small polarons and excitons in novel functional solid materials, like polymeric carbon nitrides, and tantalum oxide nitride. These materials are currently investigated for their photocatalytic application, e.g., in solar water splitting. Further applications include all-organic electronics, photovoltaics and solid-state lighting. Since these materials usually come in powder form, or as rough films, their (opto-)electronic properties cannot be determined by standard methods, like conductivity or Hall measurements. Therefore, we apply transient optical spectroscopy to obtain absorption changes and photoluminescence. From these quantities, excitation, transport and relaxation routes of photoinduced excitons and polarons can be deduced.
Recently, we could reveal the existence of long-lived transient states in polymeric carbon nitrides via time-resolved photoluminescence (TRPL). In a new project funded by the Deutsche Forschungsgemeinschaft, we are currently building up a novel setup for femtosecond transient absorption (TA) spectroscopy, based in the Joint Ultrafast Dynamics Laboratory at the FU Berlin. This setup is capable of recording TA spectra in standard transmission geometry, as well as in diffuse transmission and reflection. We will thus be able to detect transient species in highly scattering samples. We are looking forward to exciting new insights in the near future :-)
Fig. 1: Schematics of excitation, transport, and relaxation in a heterogeneous photocatalyst.
Fig. 2: Photocatalytically active polymeric carbon nitride powder.