NOVELTY - Photoactive material comprising a donor substance and an acceptor substance, is new, where the donor substance comprises or consists of at least one heteropolycyclic compound (I), or the acceptor substance comprises or consists of at least one (I), or the donor substance comprises or consists of a first heteropolycyclic compound (I) and the acceptor substance comprises a second heteropolycyclic compound (I), where the first and second compounds (I) are not the same.    USE - The photoactive material is useful in an organic solar cell or photodetector, where the organic solar cell is useful in a photoelectric conversion device and arranged as tandem cells (multi-junction solar cells) or as inverted tandem cells in the photoelectric conversion device (all claimed).    ADVANTAGE - The photoactive material: utilizes the donor and acceptor substances comprising (I) that have long-wave absorption and exhibit high open-circuit voltage in combination with the fullerene compound, thus exhibiting improved efficiency; exhibits maximum light absorption, while ensuring good charge transport.    DETAILED DESCRIPTION - Photoactive material comprising a donor substance and an acceptor substance, is new, where the donor substance comprises or consists of at least one heteropolycyclic compound of formula (I), or the acceptor substance comprises or consists of at least one (I), or the donor substance comprises or consists of a first heteropolycyclic compound (I) and the acceptor substance comprises a second heteropolycyclic compound (I), where the first and second compounds (I) are not the same.    A1, B1 = 5- or 6-membered ring that includes C atoms marked with asterisk respectively, where each ring A1 and B1 is aromatic or heteroaromatic and optionally substituted, and optionally annealed with at least one further ring not including C atoms marked with asterisk, respectively, or connected with at least one further ring by single common atom to give a spiro compound;    X1, X2 = H or substituent;    Y1, Y2 = O, S, NR1, PR1, Se or Te; and    R1 = 1-24C alkyl, 2-18C alkenyl, 2-18C alkynyl, 3-8C cycloalkyl, aryl, heteroaryl (all optionally substituted) or H.