Monitoring photochemical processes and their consequences in conjugated polymers used in organic solar cells

A. Tournebize^a^,^b, P-O Bussièrea^a^,^b, Agnes Rivaton^a^,^b, I. Fraga Domínguez^a^,^b^,^c, P.D. Topham^c, D. Bégué^d, Silvad H. Santos ^d^,^e^,^f, R.C. Hiorns^e^,^f, B. Pepin-Donat^g^,^h^,ⁱ, C. Lombart^g^,^h^,ⁱ

^aClermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand, France, France

^bCNRS, Université de Rennes 1, Campus de Beaulieu, Rennes, 35000, France

^cChemical Engineering and Applied Chemistry, Aston University, Birmingham B4 7ET

^dUniversité de Pau et des Pays de l’Adour, IPREM (ECP, CNRS-UMR 5254), 2 Avenue Président Angot, 64053 Pau, France, France

^eUniversité de Pau et des Pays de l’Adour, IPREM (EPCP, CNRS-UMR 5254), 2 Avenue Président Angot, 64053 Pau, France, France

^fCNRS, IPREM (EPCP, CNRS-UMR 5254), Hélioparc, 2 Avenue Président Angot, 64053 Pau, France, France

^gUniv. Grenoble Alpes, INAC-SPRAM, F-38000 Grenoble, France, France

^hCNRS, INAC-SPRAM, F-38000 Grenoble, France, France

ⁱCEA, INAC-SPRAM, F-38000 Grenoble, France, France

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Agnes Rivaton, presentation 034
Publication date: 5th February 2015

Polymer solar cells (PSCs) have the potential to become a highly marketable renewable energy technology if the requirements of low cost, high efficiency, and prolonged lifetimes are simultaneously fulfilled. The preservation of organic polymer solar cell (PSC) performances over time is of significant concern for their commercial development. The stability of most PSCs reported to date is limited by several factors, such asthe instability of the device electrodes and interfaces, or the morphology of the active layer. Another important PSC degradation pathway is due to inherently photo-unstable conjugated polymers in the photo-active layer, which bear continuous illumination. Photo-instability is drastically increased in the presence of atmospheric oxygen that can diffuse across the encapsulation layers to the whole device. Making long lifetime solar cells with polymers that are susceptible to degrade under light exposure could be an unrealistic challenge. Therefore, elucidating the mechanism of polymer photodegradation is a key point to develop strategies to decrease or prevent the loss of the functional properties of the material. Photobleaching is often used to evaluate and compare the photodegradation rate of conjugated polymers by measuring the decrease in the intensity of the absorption band of the material. But, photobleachingi) is only one possible consequence of the various processes responsible for the instability of the polymer, ii) is not the only criterion that can be used to give a prediction of the lifetimeiii) does not allow to elucidate the photochemical behaviour of the polymer. Thechemical reactions resulting from light exposure wo/w oxygeninclude rearrangements of the chemical structure, formation of oxidation products, cross-linking and chain scissions. Therefore, the precise identification and quantification of the photodegradation products is essential for the understanding of the degradation mechanism.Based on recent publications,we present a panel of techniques which allow to elucidate the photodegradation mechanism of the polymer, and to correlate the evolution of the chemical structure with those of the macroscopic properties of the deposits. Experimental data combined with DFT calculationsallow to establishstructure / photostability relationshipsfor conjugated polymers,paving therefore the way for the design of more resistant materials to photodegradation. Acknowledgments The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/2011 under grant agreement ESTABLIS n° 290022).

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