Prof. Natalie Banerji : Charge Carriers in Organic Semiconductors
Abstract : Doping of organic semiconductor films (chemically, electrochemically or by light absorption) enhances their conductivity for applications in organic electronics, photovoltaics, thermoelectrics and bioelectronics. However, much remains to be learnt about the properties of the conductive charges in order to optimize the design of the materials. We use ultrafast spectroscopic techniques, such as transient absorption (TA) and time-domain terahertz (TD-THz) spectroscopies, to investigate charge carriers in organic semiconductors. While femtosecond TA measurements bring insights to the nature and evolution of photoexcited species, we use TD-THz spectroscopy to gain information about the charge transport properties at the nanoscale. Processes of interest include charge generation in organic photovoltaics (OPVs), electrochemical doping in organic electrochemical transistors (OECTs) and generation of highly conductive polymer films by chemical doping. Recently, anion-exchange doping, whereby the dopant counterion is replaced by inorganic anions by exposure of a p-doped film
to an electrolyte, has been demonstrated as an effective way to overcome the limitations of chemical dopants in terms of bulkiness, stability and energetics. In parallel, the success of OECTs has fostered the development of better organic mixed ionic-electronic conductors, notably by replacing the commonly used alkyl sidechains of conjugated polymers with more polar oligoether sidechains. Inspired by the similar counterion nature of organic thin films doped either electrochemically or by anion exchange, we combine here the two concepts and find that anion exchange leads to enhanced conductivity in polythiophene and thienothiophene polymers with oligoether side chains (over 2000 S cm-1). To elucidate the origin of this high conductivity, we combine spectroscopic characterization with long-range (fourpoint-probe) and short-range (terahertz) conductivity measurements. We show that the highly
conductive samples sustain high charge densities without any drop in conductivity and without any compromise on charge mobility. Moreover, no loss in conductivity occurs when going from nanometer to millimeter distances, demonstrating highly effective charge transport over multiple length scales.
Bio : Professor Natalie Banerji is currently a Full Professor of Physical Chemistry at the University of Bern. Her research interests include the study of organic and hybrid materials
using ultrafast spectroscopic techniques, in view of solar cell and bioelectronic applications. She studied Chemistry at the University of Geneva and obtained her Ph.D. in Physical Chemistry in 2009, under the supervision of Prof. Eric Vauthey. She then moved to the University of California in Santa Barbara (USA), to work on organic solar cells during a post-doctoral stay with Nobel Laureate Prof. Alan J. Heeger (2009-2011). In 2011, she started her independent research career in Switzerland at the Ecole Polytechnique Férérale de Lausanne (EPFL) with an Ambizione Fellowship by the Swiss National Science Foundation (SNSF). She obtained an SNSF-Professorship at the University of Fribourg (Switzerland) in 2014, and was subsequently nominated tenured Associate Professor in 2015. She was President of the Chemistry Department in Fribourg form 2016-2017 and moved to Bern in 2017. In 2015, she obtained the Grammaticakis-Neumann Prize (Swiss Chemical Society) and in 2016, she was awarded an ERC Starting Grant. She is currently also part of the Swiss Research Council (Chair of Project Funding Committee) and Associate Editor of ACS Materials Letters.
to an electrolyte, has been demonstrated as an effective way to overcome the limitations of chemical dopants in terms of bulkiness, stability and energetics. In parallel, the success of OECTs has fostered the development of better organic mixed ionic-electronic conductors, notably by replacing the commonly used alkyl sidechains of conjugated polymers with more polar oligoether sidechains. Inspired by the similar counterion nature of organic thin films doped either electrochemically or by anion exchange, we combine here the two concepts and find that anion exchange leads to enhanced conductivity in polythiophene and thienothiophene polymers with oligoether side chains (over 2000 S cm-1). To elucidate the origin of this high conductivity, we combine spectroscopic characterization with long-range (fourpoint-probe) and short-range (terahertz) conductivity measurements. We show that the highly
conductive samples sustain high charge densities without any drop in conductivity and without any compromise on charge mobility. Moreover, no loss in conductivity occurs when going from nanometer to millimeter distances, demonstrating highly effective charge transport over multiple length scales.
Bio : Professor Natalie Banerji is currently a Full Professor of Physical Chemistry at the University of Bern. Her research interests include the study of organic and hybrid materials
using ultrafast spectroscopic techniques, in view of solar cell and bioelectronic applications. She studied Chemistry at the University of Geneva and obtained her Ph.D. in Physical Chemistry in 2009, under the supervision of Prof. Eric Vauthey. She then moved to the University of California in Santa Barbara (USA), to work on organic solar cells during a post-doctoral stay with Nobel Laureate Prof. Alan J. Heeger (2009-2011). In 2011, she started her independent research career in Switzerland at the Ecole Polytechnique Férérale de Lausanne (EPFL) with an Ambizione Fellowship by the Swiss National Science Foundation (SNSF). She obtained an SNSF-Professorship at the University of Fribourg (Switzerland) in 2014, and was subsequently nominated tenured Associate Professor in 2015. She was President of the Chemistry Department in Fribourg form 2016-2017 and moved to Bern in 2017. In 2015, she obtained the Grammaticakis-Neumann Prize (Swiss Chemical Society) and in 2016, she was awarded an ERC Starting Grant. She is currently also part of the Swiss Research Council (Chair of Project Funding Committee) and Associate Editor of ACS Materials Letters.
Practical information
- Informed public
- Free
Organizer
- Institute of Chemical Sciences and Engineering
Contact
- Wendy Queen
[email protected]