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THz time-domain spectroscopy of unconventional photonic and charge transport systems

English title THz time-domain spectroscopy of unconventional photonic and charge transport systems
Applicant Moser Jacques-Edouard
Number 122149
Funding scheme Project funding (Div. I-III)
Research institution Institut des sciences et ingénierie chimiques EPFL - SB - ISIC
Institution of higher education EPF Lausanne - EPFL
Main discipline Physical Chemistry
Start/End 01.10.2008 - 30.09.2010
Approved amount 153'775.00
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Keywords (10)

terahertz spectroscopy; ionic liquids; charge carrier transport; holetransporting materials; transient conductivity; organic electronics; complex conductivity; organic charge-transport materials; ultrafast laser spectroscopy; unconventional photoactive systems

Lay Summary (English)

Lay summary
The conducting and semiconducting properties of organic charge-transport materials, and hybrid inorganic-organic distributed junction systems attract considerable attention, due to several important applications in unconventional photoactive systems and organic electronics, such as light emitting diodes and photovoltaic cells. This project plans the use of a systematic technique to accurately measure the charge transport parameters and understand the carrier dynamics in these disordered systems. Terahertz time-domain spectroscopy (THz-TDS) is a very powerful technique for material studies, which covers the spectral range ~0.2-10 meV, bridging the gap between microwave and infrared experimental methods. Linear THz-TDS as a contact-less, coherent optical technique allows for direct determination of the complex conductivity of materials. Both the absorption and the dispersion of the sample can be measured directly, allowing for yielding much more accurate values of the charge transport parameters with respect to other methods. By combining THz-TDS with synchronous optical excitation, one has optical-pump THz-probe spectroscopy (OPTP) available as a powerful tool with the ability to temporally resolve phenomena at the fundamental timescales of nuclear and electronic motion. The objective of this project is to use THz spectrometry for ultrafast time-resolved conductivity studies of various materials as a function of frequency, temperature and pressure. We shall use THz-TDS and OPTP spectroscopies to study photogenerated charge carriers transport and dynamics in nanocrystalline inorganic, organic charge transport materials and nanocomposite hybrid systems. Redox-active ionic liquids, such as imidazolium iodide, hole transporting molecular liquids, such as alkoxylated triarylamines, amorphous solid hole-conducting materials, such as spiro-MeOTAD, as well as cyanine dye layers will be more particularly scrutinized. The effect of the crystallinity of the materials upon the mobility and trapping of charge carriers, as well as the influence of nanostructuring will be in the focus of this research. Charge transport in oxide nanoparticle networks of importance for dye-sensitized photovoltaic solar cells will be studied in the absence and in the presence of organic hole transporting materials filling the pores. Important results regarding the correlation of electron and holes on both sides of the distributed interface are expected to be gained through the use of THz spectroscopy.Finally, low frequency vibrations that are associated with the self trapping of charges in small polarons can as well be observed in the frequency range 0.2 - 3 THz. Application of OPTP spectroscopy is thus expected to provide invaluable information on the detailed mechanism of interfacial light-induced electron transfer and charge transport processes in dye-sensitized photoactive hybrid devices.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
132457 THz time-domain spectroscopy of unconventional photonic and charge transport systems 01.10.2010 Project funding (Div. I-III)