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Conjugated Donor-Acceptor Copolymers: Understanding Their Optoelectronic Functioning in Organic Solar Cells

Applicant Banerji Natalie
Number 136853
Funding scheme Ambizione
Research institution Institut des sciences et ingénierie chimiques EPFL - SB - ISIC
Institution of higher education EPF Lausanne - EPFL
Main discipline Physical Chemistry
Start/End 01.01.2012 - 31.12.2014
Approved amount 585'705.00
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All Disciplines (3)

Discipline
Physical Chemistry
Condensed Matter Physics
Material Sciences

Keywords (8)

Conjugated polymers; Optoelectronic properties; Donor-acceptor copolymers; Organic (bulk heterojunction) solar cells; Ultrafast spectroscopy; Photoconductivity; Photoinduced electron transfer; Photophysics

Lay Summary (French)

Lead
Nous vivons dans un monde qui a besoin d'énergie. Le soleil représente une source inépuisable mais qui n'est pas toujours facile à récolter. Le développent de cellules solaires qui permettent de convertir la lumière en électricité, est donc essentiel.
Lay summary

Contenu et objectifs du travail de recherche

Les cellules solaires généralement trouvées dans le commerce sont à base de silicone inorganique. Leur production est couteuse en argent et énergie. De nouvelles générations de cellules solaires ont donc été développées. On y compte celles dites plastiques. Elles sont principalement constituées de composés organiques (polymères conjugués, fullerènes) et sont fabriquées selon des procédés peu chers. Elles sont aussi légères et flexibles.

L’efficacité des cellules solaires plastiques frôle aujourd'hui les 10 %. Elles deviennent donc commercialement intéressantes, mais doivent encore être améliorées. Pour cela, l'interaction entre les composés photovoltaïques et la lumière, ainsi que la génération de courant électrique, doivent être mieux compris.

Dans ce projet, nous utilisons la spectroscopie résolue dans le temps et des mesures de photocourant pour mieux comprendre les cellules solaires plastiques. Il y trois principales parties à cette recherche: 1) Polymères conjugués seuls, en solution ou à l'état solide. A fin de mieux comprendre l'état excité (qui résulte de l'absorption de lumière) et son évolution dans le temps, des séries chimiques de polymères et des composés modèles sont étudiés. 2) Polymères conjugués mélangés à des fullerènes à l'état solide. Il se forme une matière qui permet la conversion de lumière en charges électriques, mais le mécanisme n'est pas bien compris. Nous utilisons la spectroscopie extrêmement rapide (femtoseconde). Des informations complémentaires sont obtenues dans différentes régions spectrales (visible, infrarouge, terahertz). 3) Etude spectroscopique de cellules solaires en marche. Cela permet d'étudier le photocorant macroscopique et l'évolution des charges à échelle femtoseconde, en parallèle.

Contexte scientifique et social du projet de recherche 

Les résultats de cette recherche vont contribuer au développement ciblé de nouveaux matériaux pour des cellules solaires organiques de plus grande efficacité.

Direct link to Lay Summary Last update: 03.01.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Importance of Unpaired Electrons in Organic Electronics
Yuen Jonathan, Wang Mingfeng, Fan Jian, Sheberla Dennis, Kemei Moureen, Banerji Natalie, Scarongella Mariateresa, Valouch Sebastian, Pho Toan, Kumar Rajeev, Chesnut Eneida, Bendikov Michael, Wudl Fred (2015), Importance of Unpaired Electrons in Organic Electronics, in Journal of Polymer Science A , 53, 287.
Spectroscopy of Charge Carrier Dynamics- From Generation to Collection
Cowan Sarah, Banerji Natalie (2015), Spectroscopy of Charge Carrier Dynamics- From Generation to Collection, in Richter Henning, Rand Barry P. (ed.), Pan Stanford Publishing, Singapore, 431.
Charge Separation Pathways in a Highly Efficient Polymer: Fullerene Solar Cell Material
Paraecattil Arun Aby, Banerji Natalie (2014), Charge Separation Pathways in a Highly Efficient Polymer: Fullerene Solar Cell Material, in Journal of the American Chemical Society, 136, 1472-1482.
Physical Chemistry of Interfaces and Nanomaterials XIII
Hayes Sophia, Silva Carlos, Banerji Natalie (ed.) (2014), Physical Chemistry of Interfaces and Nanomaterials XIII.
The Influence of Microstructure on Charge Separation Dynamics in Organic Bulk Heterojunction Materials for Solar Cell Applications
M. Scarongella, A. A. Paraecattil, E. Buchaca-Domingo, J. D. Douglas, S. Beaupré, T. McCarthy-Ward, M. Heeney, J.-E. Moser, M. Leclerc, J. M. J. Fréchet, N. Stingelin, N. Banerji (2014), The Influence of Microstructure on Charge Separation Dynamics in Organic Bulk Heterojunction Materials for Solar Cell Applications, in Journal of Materials Chemistry A, 2, 6218.
Charge Transfer Relaxation in Donor-Acceptor Type Conjugated Materials
Scarongella Mariateresa, Laktionov Andrey, Rothlisberger Ursula, Banerji Natalie (2013), Charge Transfer Relaxation in Donor-Acceptor Type Conjugated Materials, in Journal of Materials Chemistry C, 1, 2308-2319.
Physical Chemistry of Interfaces and Nanomaterials XII
Physical Chemistry of Interfaces and Nanomaterials XII, (2013), Physical Chemistry of Interfaces and Nanomaterials XII, SPIE Press, San Diego.
Sub-Picosecond Delocalization in the Excited State of Conjugated Homopolymers and Donor-Acceptor Copolymers
Banerji Natalie (2013), Sub-Picosecond Delocalization in the Excited State of Conjugated Homopolymers and Donor-Acceptor Copolymers, in Journal of Materials Chemistry C, 1, 3052-3066.
Intensity Dependent Femtosecond Dynamics in a PBDTTPD-Based Solar Cell Material
Paraecattil Arun Aby, Beaupre Serge, Leclerc Mario, Moser Jacques-E., Banerji Natalie (2012), Intensity Dependent Femtosecond Dynamics in a PBDTTPD-Based Solar Cell Material, in Journal of Physical Chemistry Letters, 3, 2952-2958.
Sensitization of fullerenes by covalent attachment of a diketopyrrolopyrrole chromophore
Banerji Natalie, Wang Mingfend, Fan Jiang, Chesnut Eneida S., Wudl Fred, Moser Jacques-E. (2012), Sensitization of fullerenes by covalent attachment of a diketopyrrolopyrrole chromophore, in Journal of Materials Chemistry, 22(26), 13286-13294.
A Close Look at Charge Generation in Polymer:Fullerene Blends with Microstructure Control
Scarongella Mariateresa, De Jonghe-Risse Jelissa, Buchaca-Domingo Ester, Causa’ Martina, Fei Zhuping, Heeney Martin, Moser Jacques-E., Stingelin Natalie, Banerji Natalie, A Close Look at Charge Generation in Polymer:Fullerene Blends with Microstructure Control, in Journal of the American Chemical Society, Just Accepted.

Collaboration

Group / person Country
Types of collaboration
Prof. Ursula Röthlisberger, ISIC, EPFL Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Walter Caseri, ETH Zürich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Mario Leclerc, Université Laval, Québec City Canada (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Clémence Corminboeuf, ISIC, EPFL Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Prof. Alan J. Heeger, Center for Polymers & Organic Solids, University of California, Santa Barbara United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Peter Hamm, Physical Chemistry Institute, University of Zürich Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Prof. Eric Vauthey, University of Geneva Switzerland (Europe)
- Research Infrastructure
Prof. Sophia Hayes, University of Cyprus Cyprus (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Prof. Andreas Hauser, University of Geneva Switzerland (Europe)
- Research Infrastructure
Prof. Kevin Sivula, ISIC, EPFL Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Prof. Yong Cao, SCUT China (Asia)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Holger Frauenrath, Materials Department, EPFL Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Prof. Jean Fréchet, King Abdullah University of Science and Technology Saudi Arabia (Asia)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Fred Wudl, Center for Polymers & Organic Solids, University of California, Santa Barbara United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Dr. Natalie Stingelin, Imperial College Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Excitonic Photovoltaics (XPV) 2014 Talk given at a conference Ultrafast Stark Spectroscopy in OPV Devices with Microstructure Control 15.08.2014 Telluride, United States of America Banerji Natalie;
Next Generation Solar, Photovoltaics Canada, National Scientific Conference Talk given at a conference The Effect of Bulk Heterojunction Structure On Charge Separation in Organic Solar Cells 15.05.2014 Montréal, Canada Banerji Natalie;
6th International Conference on Hybrid and Organic Photovoltaics (HOPV) Talk given at a conference The Effect of Microstructure and Charge Separation Pathway on Carrier Generation in Organic Solar Cells 12.05.2014 Lausanne, Switzerland Banerji Natalie;
Seminar Series on Photoinduced Dynamics of Molecular Aggregates Individual talk The Effect of Microstructure on Charge Generation in Organic Solar Cells 06.02.2014 Würzburg, Germany Banerji Natalie;
Annual NCCR-MUST Assembly Meeting Poster THz Time Domain Spectroscopy and Transient Absorption Spectroscopy of Charge Carrier Dynamics in Conjugated Polymer 08.01.2014 Engelberg, Switzerland Scarongella Mariateresa;
5th International Symposium on Emergence of Highly Elaborated π-­Space and Its Function Talk given at a conference Short-­Lived Delocalization and Charge Transfer Relaxation in Conjugated Donor-­Acceptor Copolymers 24.10.2013 Nagoya, Japan Banerji Natalie;
Structure-­Property Relationships of Molecular Precursors to Organic Electronics, CECAM Talk given at a conference Organic Solar Cell Materials Visited by Ultrafast Spectroscopy from the Building Blocks to Working Devices 22.10.2013 Lausanne, Switzerland Banerji Natalie;
Fall Meetings of the Swiss Chemical Society Poster THz Time Domain Spectroscopy and Transient Absorption Spectroscopy of Charge Carrier Dynamics in Conjugated Polymers 06.09.2013 Lausanne, Switzerland Scarongella Mariateresa;
European Conference on Molecular Electronics, ECME Talk given at a conference Conjugated Polymer:Fullerene Blends Visited by Transient Absorption Spectroscopy from the Visible to Terahertz Range 03.09.2013 London, Great Britain and Northern Ireland Banerji Natalie;
Physical Chemstry of Interfaces and Nanomaterials XII Talk given at a conference THz Time Domain Spectroscopy of Charge Carrier Dynamics in Conjugated Polymers 25.08.2013 San Diego, United States of America Scarongella Mariateresa;
NCCR-­MUST Site Visit Poster Ultrafast Processes in Organic Solar Cells 20.06.2013 Zürich, Switzerland Banerji Natalie;
Young Faculty Meeting 2013 Talk given at a conference Ultrafast Processes in Conjugated Materials 06.06.2013 Bern, Switzerland Banerji Natalie;
Annual NCCR-MUST Assembly Meeting Talk given at a conference Women in Science 08.01.2013 Engelberg, Switzerland Banerji Natalie;
Materials Research Society (MRS) Fall Meeting Talk given at a conference Ultrafast Excited-­‐State Dynamics of PBDTTPD and PBDTTPD:PCBM Thin Films Probed by Transient Absorption Spectroscopy 25.12.2012 Boston, United States of America Banerji Natalie;
Materials Research Society (MRS) Fall Meeting Poster Delocalization versus Charge Transfer Character in the Optical Transitions of Donor-­Acceptor Copolymers 25.12.2012 Boston, United States of America Banerji Natalie;
EPFL Photonics Day Poster THz Time Domain Spectroscopy of Charge Carriers in Conjugated Donor-­‐Acceptor Copolymers 26.11.2012 Lausanne, Switzerland Scarongella Mariateresa;
Black Forest Focus on Soft Matter 8 Poster Ultrafast Excited-­State Dynamics of PBDTTPD and PBDTTPD:PCBM Thin Films 10.10.2012 Schluchsee, Germany Banerji Natalie;
Swiss Physical Society (SPS) Annual Meeting Talk given at a conference Breaking Down the Problem to Understand the Photophysics of Conjugated Polymers 22.06.2012 Zürich, Switzerland Banerji Natalie; Scarongella Mariateresa;
Visit to Imperial College (Centre for Plastic Electronics) Individual talk Delocalization versus Charge Transfer Character in the Optical Transitions of Conjugated Donor-­Acceptor Copolymers 14.06.2012 London, Great Britain and Northern Ireland Banerji Natalie;
Gordon Research Conference “Electronic Processes in Organic Materials” Poster Delocalization versus Charge Transfer Character in the Optical Transitions of Conjugated Donor-­Acceptor Copolymers 03.06.2012 Lucca, Italy Banerji Natalie;
Annual NCCR-MUST Assembly Meeting Poster Implications of Ultrafast Relaxation in Conjugated Polymers on the Functioning of Organic Solar Cells 08.01.2012 Lenk, Switzerland Banerji Natalie;


Self-organised

Title Date Place
“Physical Chemistry of Interfaces and Nanomaterials XIII” symposium at the SPIE Nanoscience and Engineering conference 17.08.2014 San Diego, United States of America
“Physical Chemistry of Interfaces and Nanomaterials XII” symposium at the SPIE Nanoscience and Engineering conference 25.08.2013 San Diego, United States of America
Department seminar given by Prof. Michel Schott 10.12.2012 Lausanne, Switzerland
Department seminar given by Dr. Natalie Stingelin 16.11.2012 Lausanne, Switzerland
Organic Photovoltaic Seminars (weekly) 27.06.2012 Lausanne, Switzerland

Communication with the public

Communication Title Media Place Year
Talks/events/exhibitions Cérémonie des Diplômes 2012 de la Section de chimie et biochimie, Université de Genève Western Switzerland 2012

Awards

Title Year
Grammaticakis-Neumann Prize (par SCS) 2015

Abstract

Conjugated polymers combine semiconducting electronic behavior with high optical absorption in the visible, plastic-like mechanical properties and easy solution processing. This carbon-based class of materials has therefore emerged over the last few decades as an organic alternative to expensive inorganic semiconductors in optoelectronic applications. Conjugated polymers have been successfully used in light emitting devices, transistors, photo-detectors and organic solar cells. In the solar cells, the solid thin film active layer is typically a blend of the polymer with a fullerene derivative. Spontaneous phase separation leads to the formation of a nanoscale bulk heterojunction (BHJ) material in which there is an interpenetrating polymer:fullerene morphology. Ultrafast photoinduced charge separation (CS) between the polymer donor and the fullerene acceptor is the initial step in the generation of mobile charge carriers and this is favored by the high donor-acceptor interfacial area in the BHJ. The mobile charge carriers can then travel to the electrodes along phase-separated fullerene and polymer networks. The power conversion efficiency in polymer photovoltaic devices has enjoyed a leap form 3% to 8.3% over the last ten years. This rise can largely be attributed to the development of novel donor-acceptor copolymers of an electron-rich unit and an electron-poor unit. The objective of the currently proposed research is not to develop or optimize any applications, but rather to understand why and how solar cells containing conjugated donor-acceptor copolymers work. Indeed, the fundamental Science of the processes underlying the photovoltaic functioning clearly lags behind the rapid advances in device efficiency. The latter are therefore often achieved by trial and error, which involves time-consuming synthesis and laborious device testing/optimization with a large number of materials, only few of which will be successful. Feedback from a fundamental optoelectronic understanding contributes to planned strategy in both the synthesis and solar cell applications, so that higher efficiency can be achieved and this faster. Important questions that need to be addressed to that aim include:• How does the strength of the internal charge transfer character influence the optoelectronic properties of donor-acceptor copolymers?• How can CS in BHJ blends occur in <100 fs when the polymer photoexcitation has to travel by up to 10 nm to reach a fullerene interface?• How does charge recombination (a loss mechanism that reduces efficiency) occur in working solar cells under applied voltage bias?The persisting lack of clarity about the optoelectronic properties and photophysics of polymer solar cell, in spite of ongoing research efforts in the field, arises from various factors. Those include the complexity of conjugated polymers and particularly donor-acceptor copolymers, the limited availability of the non-commercial materials to many photophysically specialized groups, the limited availability of versatile spectroscopic tools to groups who have access to the materials and develop applications, and the difficulty to compare and reproduce results if the experimental conditions (polymer quality, processing, excitation intensity) are not carefully controlled. I therefore suggest a very systematic investigation of the optoelectronic functioning of polymer solar cells, using purely optical spectroscopic techniques as well as more electrical measurements. In order to answer the above and related questions, I plan to lead the investigation from an understanding of the “simplest” systems (the pristine conjugated polymers and even their isolated repeat units), via polymer:fullerene BHJ blends, to working photovoltaic devices. The proposed research relies on the use of a large variety of experimental tools to yield complementary information under well-controlled conditions. Where time-resolved optical measurements are concerned, I will go beyond the most-commonly employed visible transient absorption experiments and will apply very specialized techniques: Time-resolved fluorescence with very high time resolution (<50fs), femtosecond optical-pump terahertz-probe spectroscopy, femtosecond transient absorption with mid-infrared probing, and transient reflectivity (femtosecond and nanosecond resolution) on working solar cells. All apparatuses will be at my disposal at the host institution (École Polytechnique Fédérale de Lausanne, EPFL) in the group of Prof. Jacques Moser, except for the transient infrared setup which will be used in collaboration with the recognized group of Prof. Peter Hamm (University of Zürich), linked to EPFL through the NCCR MUST network. Electrical steady-state photoconductivity measurements, with an apparatus that will be developed if possible by a PhD student, will complement the purely optical methods. Furthermore, the spectroscopic results obtained with working devices can be related to their current-voltage characteristics, since I will have access to the photovoltaic cell characterization equipment in the group of Prof. Michael Grätzel (EPFL, Lausanne). Strength of the project also arises through the often exclusive availability of novel donor-acceptor copolymers through collaborations with internationally leading groups in polymer synthesis: Prof. Fred Wudl (University of California, Santa Barbara) and Prof. Mario Leclerc (Université Laval, Québec City). I will also have access to materials and optimized solar cell devices through collaboration with Nobel Laureate Prof. Alan J. Heeger (University of California, Santa Barbara), pioneer in the Science and applications of conjugated polymers. Moreover, assistance with polymer processing can be obtained from the group of Dr Frank Nüesch (Laboratory for Functional Polymers, Empa, Switzerland), an active collaborator of the Moser group. The majority of investigated compounds (examples are shown in Fig. 11 of the project proposal) have never been studied from a photophysical point of view, especially not with the proposed array of experimental tools. This access to novel materials, combined with a complete set of pertinent measurement techniques and my personal experience with ultrafast spectroscopy and conjugated polymers, promises success an innovation in the proposed research.
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