Direct influence of morphology on current generation in conjugated polymer:methanofullerene solar cells measured by near-field scanning photocurrent microscopy

We present near-field scanning photocurrent microscopy (NSPM) images of MEH-PPV:PCBM bulk heterojunction solar cells prepared by spin-coating from toluene and chlorobenzene. By utilising the NSPM technique, we demonstrate directly the influence of nano-scale phase-segregation features on local current generation. In particular, by using 100 nm aperture tips we show that the 500 nm diameter phase-segregated island features in toluene prepared films contribute significantly less to the overall current than the surrounding regions. Chlorobenzene prepared films show more uniform current generation on the length scale of 100 nm, with the photocurrent varying by only 5%. (C) 2004 Elsevier B.V. All rights reserved.