© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim phys. stat. sol. (RRL) 1, No. 5, 193– 195 (2007) / DOI 10.1002/pssr.200701131 www.pss-rapid.com pss Correlation of atomic force microscopy detecting local conductivity and micro-Raman spectroscopy on polymer–fullerene composite films Jan C ˇ ermák *, 1 , Bohuslav Rezek 1 , Věra Cimrová 2 , Drahomír Výprachtický 2 , Martin Ledinský 1 , Tomáš Mates 1 , Antonín Fejfar 1 , and Jan Kočka 1 1 Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i., Cukrovarnická 10, 16253 Prague 6, Czech Republic 2 Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Heyrovského náměstí 2, 16206 Prague 6, Czech Republic Received 13 July 2007, revised 10 August 2007, accepted 13 August 2007 Published online 17 August 2007 PACS 68.37.Ps, 68.55.Nq, 73.50.Pz, 78.30.Na, 81.05.Qk, 81.05.Tp * Corresponding author: e-mail cermakj@fzu.cz © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Organic photovoltaic devices [1, 2] are still not able to compete with conventional inorganic solar cells mainly due to the lower power conversion effi- ciency (~ 5% [3]). Improvements can be achieved by better understanding the generation and transport of photogener- ated charge carriers. In the past the current-sensing atomic force microscopy (CS-AFM) [4, 5] has been used for the study of microscopic morphology and local electronic transport properties of heterostructural silicon thin films, leading to remarkable results [6, 7]. In the CS-AFM, a DC voltage between the sample and the AFM tip is applied when scanning in contact regime and the electric current is detected. Therefore, both microscopic morphology and lo- cal conductivity can be characterized simultaneously. Ap- plying this technique to heterostructural organic thin films faces the problem of establishing mechanical and electrical contact to the soft organic materials without compromising their integrity. So far, CS-AFM has been used for a few types of organic materials. Ni-implanted polyethylene terephthalate films needed to be cooled to low tempera- tures (down to 160 K) for obtaining reliable and reproduci- ble contact-AFM measurements [8]. The study of electro- deposited polypyrrole films by CS-AFM revealed a sig- nificant dependence of film conductivity on electrolyte composition [9]. Alexeev et al. studied the electronic and structural properties of a blend of two semiconducting polymers (donor – acceptor system) by CS-AFM [10] al- lowing only indirect deduction of microscopic material composition and hence relevant electronic properties. In this work, we report on a successful use of CS-AFM at ambient conditions to obtain reproducible microscopic maps of local conductivity on soft heterostructural organic thin films without any damage. Furthermore, we correlate this data with microscopic morphology measured by tap- ping mode AFM (TM-AFM), local electron work functions deduced from Kelvin force microscopy (KFM) and mate- rial composition detected by micro-Raman spectroscopy. We show that combination of all these techniques enables significantly enhanced insight into the properties of het- erostructural composite films. Thin hetero-junction composite films of polymer (electron donor) and fullerene (electron acceptor) are prepared on in- dium-tin-oxide coated glass by spin-coating from solution in dichlorobenzene. Optimized atomic force microscopy (AFM) parameters allowed us to scan these soft composite films in contact mode and to measure their local conductivity with high lateral resolution by current-sensing AFM. The mor- phology and local conductivity data are correlated with Kel- vin force microscopy and micro-Raman mapping and dis- cussed with view to their photovoltaic properties. Regions with both compounds present are compared to areas where the components segregated, acting as shunts of the junction.