Tracing charge transfer states in polymer: fullerene bulk-heterojunctions

Charge transfer state emission in organic bulk-heterojunctions has been demonstrated to be an important loss mechanism for this reason a better understanding of the nature and origin of the charge transfer state is fundamental for the improvement of organic solar cells. Here, the relationship between photophysical and morphological features of a prototypical organic bulk-heterojunction is investigated in blends with different donor-acceptor ratios. By correlating imaging with photoluminescence spectra measured in different areas of the blends, the charge transfer state emission is unambiguously assigned to microscopical regions in which the intermixing of the two organic semiconductors is higher.