Dresden 2011 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 12: Organic Semiconductors II: Solar Cells B (jointly with HL, DS)
CPP 12.7: Talk
Tuesday, March 15, 2011, 12:15–12:30, ZEU 222
Towards Ideal Morphology of Polymer Bulk Heterojunction Solar Cells — •Chetan Raj Singh1, Michael Sommer2,3, Marcel Himmerlich1, André Wicklein3, Stefan Krischok1, Mukundan Thelakkat3, and Harald Hoppe1 — 1Institute of Physics, Ilmenau University of Technology, Germany — 2Department of Chemistry, University of Cambridge, United Kingdom — 3Applied Functional Polymers, University of Bayreuth, Germany
We present the thorough optimization of block copolymer (BCP) based polymer solar cells utilizing a blend of a self-assembling P3HT-b-PPerAcr BCP and an PPerAcr acceptor homopolymer. As an effect of increasing acceptor content in the block copolymer/homopolymer blend, we observe a continuous rise in the open circuit voltage (Voc) and the short circuit current (Isc) leading to an overall improved photovoltaic performance. The improved performance with increasing acceptor content is attributed to (a) an increase of the acceptor domain size leading to improved charge transport and to (b) a reduced recombination of charge carriers at the cathode interface due to the surface segregation of the acceptor. The surface segregation of the acceptor is identified by atomic force microscopy and X-ray photoelectron spectroscopy. Furthermore we show that by deliberately introducing an acceptor buffer layer at the cathode interface, we are able to control Voc at relatively high values (~ 640 mV), independently of the bulk heterojunction morphology underneath.