received by the International Bureau on 20 March 2015 (20.03.2015) 1. A photoactive material comprising a donor substance and an acceptor substance, wherein a. the donor substance comprises or consists of one or more compounds of formula (I), or b. the acceptor substance comprises or consists of one or more compounds of formula (I), or c. the donor substance comprises or consists of a first compound of formula (I) and the acceptor substance comprises or consists of a second compound of formula (I) with the proviso that the first and second compound are not the same, wherein the compound of formula (I) is selected from the group consisting of:

wherein Alk in each case is independently of each other either linear alkyl having 1 to 20 carbon atoms or branched alkyl having 1 to 20 carbon atoms.

2. The photoactive material according to claim 1 , wherein the compound of formula (I) is selected from the group of compounds of formulae 1 to 51 :

3. The photoactive material according to claim 1 or 2, wherein the donor substance comprises or consists of one or more compounds of formula (I) as defined in claim 1 or 2, and wherein the acceptor substance comprises or consists of one or more compounds selected from the group consisting of

(i) fullerenes and fullerene derivatives, preferably selected from the group consisting of C₆₀, C₇₀ and [6,6]-phenyl-C₆₁-butyric acid methyl ester, and

(ii) 3,4,9,10-perylenetetracarboxyl-bisbenzimidazole (PTCBI). 4. A solar cell or a sensor, the solar cell or sensor comprising a photoactive material according to any of claims 1 to 3.

5. Use of a compound of formula (I) as defined in claim 1 or 2 as donor substance or as acceptor substance in a photoactive material, wherein preferably the photoactive material is part of a layer of a donor-acceptor bilayer or part of a donor- acceptor mixed layer (bulkheterojunct!on, BHJ). 6. Use according to claim 5, wherein the photoactive material is part of a solar cell or sensor. 7. A photoelectric conversion device comprising or consisting of two or more solar cells according to claim 4, wherein the solar cells are arranged as tandem cells (multi-junction solar cells). 8. A photoelectric conversion device according to claim 7, wherein the organic solar cells are arranged as inverted tandem cells. 9. A compound of formula (I) as defined in claim 1 or 2 for use as donor substance or as acceptor substance in a photoactive material, wherein preferably the photoactive material is part of a layer of a donor-acceptor bilayer or part of a donor- acceptor mixed layer (bulkheterojunction, BHJ),