Nanoscale morphology in bulk-heterojunction solar cells

Recently the research interest in plastic solar cells using the bulk heterojunction concept [1-5] has been increasing. Here we report results on conjugated polymer/fullerene blends based solar cells, which exhibit a dramatic increase in solar power conversion efficiency to more than 3% in the last few years [6-8]. A key parameter for the device efficiency is the nanoscale morphology of the distribution of donor and acceptor species within the photoactive layer. A suitable morphology must provide proximity of the blended compounds for an efficient charge transfer [9] and conducting percolation pathways for electrons and holes to their respective electrodes. To meet these requirements it is necessary to understand the formation of the active layers cast from solution. In this paper we report on complementary AFM, SEM, TEM and photoluminescence measurements enabling us to differentiate between donor and acceptor phases.