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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 132457
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 01.10.2010 - 30.04.2012
Approved amount 136'675.00
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Keywords (8)

Terahertz time-domain spectroscopy; Complex conductivity; Hole-transporting materials; Organic electronics; Ultrafast laser spectroscopy; Electron transfer dynamics; Charge carrier dynamics; Charge transport

Lay Summary (English)

Lead
Lay summary
Organic bulk-heterojunction photovoltaic cells rely on conductive organic polymers, organic solids or small organic molecules for light absorption and charge transport. The interest in organic solar cells has recently increased due to their advantages over conventional photovoltaics: they have a low impact on the environment, manufacturing is easy, and because they can be attached to flexible materials they can be put on many things (like plastic ID or bank cards, clothing, mobile phones and laptops). They are even sufficiently cheap for being associated with disposable objects. So far, these devices have shown rather modest power conversion efficiencies which could be related to inefficient charge transport or morphology problems resulting in fast charge recombination. The objective of this project is to study charge transport properties of unconventional photonic and charge transport materials, such as nanocrystalline inorganic, organic charge transport materials and nanocomposite hybrid systems and to identify the limiting factors in solar cell performance. 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. Electron transfer dynamics at the junction between such materials will also be in the focus of this research.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, and this is expected to give 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. 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.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Conduction through Viscoelastic Phase in a Redox-Active Ionic Liquid at Reduced Temperatures
Thorsmølle Verner K., Topgaard Daniel, Brauer Jan C., Zakeeruddin Shaik M., Grätzel Michael, Moser Jacques-E. (2012), Conduction through Viscoelastic Phase in a Redox-Active Ionic Liquid at Reduced Temperatures, in Advanced Materials, 24, 781-784.
Synthesis and characterization of high-photoactivity electrodeposited Cu2O solar absorber by photoelectrochemistry and ultrafast spectroscopy
Paracchino Adriana, Brauer Jan Cornelius, Moser Jacques-Edouard, Thimsen Elijah, Grätzel Michael (2012), Synthesis and characterization of high-photoactivity electrodeposited Cu2O solar absorber by photoelectrochemistry and ultrafast spectroscopy, in J. Phys. Chem. C, 116, 7341-7350.
Temperature-dependent ordering phenomena of a polyiodide system in a redox-active ionic liquid
Thorsmølle Verner K., Brauer Jan Cornelius, Zakeeruddin Shaik M., Grätzel Michael, Moser Jacques-E. (2012), Temperature-dependent ordering phenomena of a polyiodide system in a redox-active ionic liquid, in J. Phys. Chem. C, 116, 7989-7992.
Extraordinarily Efficient Conduction in a Redox-Active Ionic Liquid
Thorsmolle VK, Rothenberger G, Topgaard D, Brauer JC, Kuang DB, Zakeeruddin SM, Lindman B, Gratzel M, Moser JE (2011), Extraordinarily Efficient Conduction in a Redox-Active Ionic Liquid, in CHEMPHYSCHEM, 12(1), 145-149.
Photoinduced Interfacial Electron Transfer and Lateral Charge Transport in Molecular Donor-Acceptor Photovoltaic Systems
Punzi A, Brauer JC, Marchioro A, Ghadiri E, de Jonghe J, Moser JE (2011), Photoinduced Interfacial Electron Transfer and Lateral Charge Transport in Molecular Donor-Acceptor Photovoltaic Systems, in CHIMIA, 65(5), 353-355.
Transient photoconductivity of dye-sensitized TiO2 nanocrystalline films probed by optical pump-THz probe spectroscopy
Brauer Jan C., Teuscher Joël, Punzi Angela, Moser Jacques-E. (2011), Transient photoconductivity of dye-sensitized TiO2 nanocrystalline films probed by optical pump-THz probe spectroscopy, in Chergui M. (ed.), Oxford University Press, New York, 358-360.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Swiss Photonics and Laser Network Workshop on Femtosecond Energy Harvesting and Storage Talk given at a conference Third-generation photovoltaic cells: Beyond the present state-of-the-art 13.06.2012 Lausanne, Switzerland Moser Jacques-Edouard;
Hybrid and Organic Photovoltaics Conference (HOPV12) Talk given at a conference Dynamics of interfacial charge transfer excitons at dye-sensitized donor/acceptor hybrid heterojunction 06.05.2012 Uppsala, Sweden Moser Jacques-Edouard;
SLS-PSI Seminar Individual talk Dynamics of interfacial electron transfer and charge transport processes in nanostructured bulk heterojunction solar cells 23.03.2012 PSI Villigen, Switzerland Moser Jacques-Edouard;
NCCR MUST Annual meeting Talk given at a conference Dynamics of Electron Transfer Processes in Third generation Solar Cells 14.01.2011 Lenk, Switzerland Moser Jacques-Edouard;


Self-organised

Title Date Place

Communication with the public

Communication Title Media Place Year
New media (web, blogs, podcasts, news feeds etc.) A breakthrough in our understanding of ionic liquids YouTube International 2011

Associated projects

Number Title Start Funding scheme
122149 THz time-domain spectroscopy of unconventional photonic and charge transport systems 01.10.2008 Project funding (Div. I-III)
125760 NCCR MUST: Molecular Ultrafast Science and Technology (phase I) 01.07.2010 National Centres of Competence in Research (NCCRs)

Abstract

The conducting and semiconducting properties of organic charge-transport materials, and hybrid inorganic-organic distributed heterojunction systems have attracted considerable attention over the past decade due to several important applications in unconventional photoactive systems and organic electronics, such as light emitting diodes and photovoltaic cells. A systematic technique to accurately measure the charge transport parameters, and to understand the carrier dynamics in these disordered systems is yet to be fully developed. 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 in particular to discriminate between free charge carrier and excitonic transport. Optical-pump THz-probe spectroscopy (OPTP) is a powerful tool to temporally resolve phenomena at the fundamental timescales of nuclear and electronic motion. This method probes charge transport over nano-scale distances, allowing for the determination of the intrinsic mobility of charge carriers in a material.The objective of the present project is to use THz spectrometry for ultrafast time-resolved conductivity studies of various materials as a function of frequency, temperature and pressure. We will utilize 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, hole transporting molecular liquids, such as alkoxylated triarylamines, amorphous solid hole-conducting materials, such as spiro-MeOTAD, cyanine dye and DPP 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 - 4 THz. Application of OPTP spectroscopy will thus provide invaluable information on the detailed mechanism of interfacial light-induced electron transfer and charge transport processes in dye-sensitized photoactive hybrid devices.
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