HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 164
C48 - Light induced effects in PCBM:P3HT blend films
Andrzej Dzwilewski, Ana Sofia Anselmo, Krister Svensson, Ellen Moons
Karlstad University, Universitetsgatan 2, Karlstad, 65188, SE
Blends of poly(3-hexylthiophene) (P3HT), and phenyl-C61-butyric acid methyl ester (PCBM)
are model systems for studies of active material for organic bulk hetero-junction solar cells.
Recently we have observed light induced changes in transport properties in the active
materials based on P3HT:PCBM blends measured in field-effect transistors [1]. The Fullerene
component of the blends isknown to form dimers under exposure to visible laser light [2].
Additionally light exposure of PCBM:P3HT blends affects the morphology of the blend films,
increasing the degree of already present polymer enrichment at the free surface. Polymer
enrichment has also been seen in non illuminated films of similar systems [3,4,5]. Light
induced morphology changes are of great interest for understandingthe long-term
performance of organic solar cells as they may affect their lifetime.
Here we present the results of a systematic Near Edge X-ray Absorption Fine Structure
(NEXAFS) spectroscopy study on thin films of P3HT and PCBM (both in pure form and in blends
of the two) under different conditions: as cast films, films illuminated in air and films
illuminated under UHV conditions. We have observed clear changes in the NEXAFS spectra of
PCBM and PCBM:P3HT blends, while pure P3HT was not affected by visible laser-light
exposure. Our data suggest that oxygen plays an important role in photo-dimerization of PCBM
as films illuminated in UHV were much less affected by light, than films illuminated in air.
Observed changes in NEXAFS spectra suggest a reorganization of the molecules caused by light
illumination for PCBM, both in pure form and in blends. Light induced changes in film
morphology are of key importance for understanding light induced degradation effects in
organic solar cells.
References
[1] A. Dzwilewski, P. Matyba, L. Edman J. Phys. Chem. B 2010, 114, 135
[2] A. Dzwilewski, T. Wågberg, L. Edman J. Am. Chem. Soc. 2009, 131, 4006
[3] B. Xue, B. Vaughan, C.-H. Poh, K. B. Burke, L. Thomsen, A. Stapleton, X. Zhou, G.W. Bryant, W. Belcher, P. C.
Dastoor J. Phys. Chem. 2010, 114, 1
[4] A. S. Anselmo, L. Lindgren, J. Rysz, A. Bernasik, A. Budkowski, M. R. Andersson, K. Svensson, J. van Stam, E.
Moons Chem. Mater. 2011, 23, 2295
[5] Germack, D. S.; Chan, C. K.; Hamadani, B. H.; Richter, L. J.; Fischer, D. A.; Gundlach, D. J.; DeLongchamp, D. M.
Appl. Phys. Lett. 2009, 94, 233303.
© SEFIN 2012