In scientific papers on organic solar cells, all kinds of efficiencies are reported. The aim of this paper is to discuss some of the valuable as well as some of the less valuable efficiencies. However, the main aim of this discussion is to get a deeper insight in the efficiency limiting processes of state of the art molecular organic solar cells. As an example our three layer cell made from 20 nm N, N＇-Dimethyl-3,4:9, 10-perylenbis (carboximid) (MPP), 30 nm Zinc-phthalocyanine (ZnPc) containing 50% C-60 and 50 nm ZnPc is used. It is shown that here for the first time the efficiency of a purely organic solar cell is not limited anymore mainly by the achieved current efficiency but rather the obtained open-circuit voltage and the fill factor. (C) 2000 Elsevier Science B.V. All rights reserved.