We show that the performance of organic solar cells can be strongly improved using PIN structures with doped wide-gap transport layers and a phthalocyanine-fullerene blend as a photoactive layer. Such cells only absorb light in the photoactive region and thus avoid recombination losses at the contacts and make optimum use of the light reflected at the top contact. They reach approximately 1.9% power efficiency at simulated AM 1.5 illumination, nearly 100% internal quantum efficiency and a fill factor of approximately 50%. We show that it is possible to stack two or more of these optically thin PIN cells into one sandwich structure without significant losses. This principle should soon enable us to prepare organic solar cells with outstandingly high efficiency. In the solar cells, a new technique of n-doping by cationic dyes is used. Using fullerene or perylene derivatives as a matrix, it yields thermally very stable layers with high conductivity. (C) 2003 Elsevier B.V. All rights reserved.