NOVELTY - A terrylene compound is new.    USE - As electron donor material in organic solar cells e.g. tandem cell (claimed).    ADVANTAGE - The semiconductive organic absorber material (I) has long-wave absorption, which in combination with fullerenes or fullerene derivatives, provides tandem cells with high open-circuit voltage and acceptable short-circuit current. The terrylene compounds are suitable for production of functioning solar cells by vapor deposition processes. In the course of vaporization, there is no decomposition to a degree which prevents use in solar cells. The compound (I) allows a new generation of solar cells which are much less expensive than solar cells made from silicon or other inorganic semiconductors, such as cadmium indium selenide or cadmium telluride.    DETAILED DESCRIPTION - A terrylene compound of formula (I) is new.    R1-R4=H, or optionally substituted alkyl, aryl, thiophenyl or oligothiophenyl;or    at least two adjacent radicals selected from R1-R4 radicals, together with the carbon atoms of the benzene ring to which they are bonded=a fused ring system having 1-8 further rings;    A with the carbon atoms to which it is bonded=a fused monocyclic, dicyclic, tricyclic, tetracyclic, pentacyclic or hexacyclic ring system (which optionally bears at least one substituent) (preferably a compound selected from 6 compounds of formulae as given in the specification e.g. compound of formula -C(=O)-N(R23)-C(=O)-, or cyclic compound of formula (XVIc) or (XVId));    R23=H, alkyl, aryl, alkaryl or aralkyl;    R27-R29=alkyl, aryl, aralkyl or alkaryl (all optionally substituted);or    two R27 and/or R28 radicals or two R29 radicals bonded to adjacent carbon atoms=a fused benzene ring;    p,q and r=0-2 .    INDEPENDENT CLAIMS are included for the following:    (1) an organic solar cell with a photoactive region comprising at least one organic donor material in contact with at least one organic acceptor material, where the donor material and acceptor material forming a donor-acceptor heterojunction, and the photoactive region comprising at least one terrylene compound (I); and    (2) preparation of terrylene compound of formula (I).