Project Details
Projekt
Polaronic charge transport in novel solid-state photocatalysts for solar-fuel production
Applicant
Dr. Christoph Merschjann
Subject Area
Experimental Condensed Matter Physics
Term
from 2014 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 259681461
The proposed project is aimed at quantitative investigations of light-induced charge-transport processes in novel materials for heterogeneous photocatalysis. It is expected that this charge transport is of hopping type rather than band-like for a substantial number of these novel materials. This assumption is founded on experimental findings documented in the literature for some materials recently used in heterogeneous photocatalysis. The material classes under study are polymers and metal oxynitrides, respectively, of which two prototypical materials are in the focus of the proposed investigations. The former class will be substitutionary investigated on polymeric carbon nitride, for which recent publications by the applicant point to a hopping transport of photo-induced molecular excitons. The second material will be tantalum oxynitride, TaON. The optical properties of TaON exhibit strong similarities to those found in related materials like lithium niobate or lithium tantalate, for which a hopping charge transport via small polarons could be verified. It is therefore expected that the charge transport for TaON is also of polaronic nature. In the course of the project the light-induced charge transport will be investigated via ultrafast time-resolved optical spectroscopy. Therefore a combination of transient absorption and luminescence measurements is envisaged. From the obtained quantitative data, the spatial density and temporal development of light-induced charge carriers is deduced. Herein, the nature of the charge transport determines in a characteristic way the duration and shape of the transient absorption and luminescence, such that the transport mechanism can be deduced from the measured quantities. This will lead to the determination of important quantities like carrier density, electrical photo- and dark conductivity, as well as the lifetime of separated carriers in the bulk and on the surface of the photocatalyst. All these quantities are crucial to the performance of the catalyst. Since the materials under study are in powder form, a new optical setup for the quantitative determination of transient optical properties has to be developed and evaluated. Obtaining the underlying phenomena (e.g., charge transport) from the measured transient data is not a trivial process. Therefore, computer simulations of possible transport models will be pursued parallel to the measurements. The above named quantities will be determined by comparison of experimental and simulational results. It is to be expected that for both linear and nonlinear optical processes, quantum yields will thus be determinable, thus facilitating an assessment of the materials under study.
DFG Programme
Research Grants
International Connection
France
Major Instrumentation
Czerny-Turner imaging spectrograph
Instrumentation Group
1800 Spektralphotometer (UV, VIS), Spektrographen (außer Monochromatoren 565)
