Raman spectroscopic identification of fullerene inclusions in polymer/fullerene blends

Thin films of the conjugated polymer poly(3-hexylthiophene) (P3HT) and blends of the soluble fullerenederivative[6,6]-phenyl C-61-butyric acid methyl ester (PCBM) with P3HT - a well studied but not completely understood donor-acceptor system for organic solar cells - have been studied by means of UV-visible absorption and resonant Raman spectroscopy. Additionally, we have employed atomic force microscopy phase imaging to characterize the nanomorphology of the P3HT : PCBM thin film, revealing a close intermixing of two phases with domain sizes ranging from a few to several tens of nanometers. A systematic analysis of pristine polymer and blend Raman spectra provides evidence that features attributable to PCBM, possibly even depending on the charge state of the fullerene molecule, can be observed. Hence our results suggest that fullerene inclusions in polymer/fullerene blends can be identified via Raman spectroscopy. Copyright (C) 2011 John Wiley & Sons, Ltd.