TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The fullerene is not phenyl-C61-butyric-acid-methyl-ester (PC61 BM). The conjugated polymer comprises repeating units of the following formula 1, where the conjugated polymer is not poly (3-hexylthiophene-2, 5-diyl) (P3HT).Y'=independently selected from N, C-H, and C-R1;R1=selected from 1-30C straight-chain and branched alkyl groups;X1=independently selected from S and Se;R=independently selected from straight-chain, branched, and cyclic alkyl with 2-40C atoms, where non-adjacent C atoms are optionally replaced by -O-, -S-, -C (O) -, -C (O-) -O-, -O-C (O) -, -O-C (O) -O-, -CR0=CR00-, or -CC-, and where H atoms are optionally replaced by F, Cl, Br, I, or CN or denote aryl, heteroaryl, aryloxy, heteroaryloxy, arylcarbonyl, heteroarylcarbonyl, arylcarbonyloxy, heteroarylcarbonyloxy, aryloxycarbonyl, or heteroaryloxycarbonyl having 4-30 ring atoms unsubstituted or substituted by non-aromatic groups;R0 and R00=independently a straight-chain, branched, or cyclic alkyl group; andAr1 and Ar2=independently selected from unsubstituted or substituted monocyclic, bicyclic, and polycyclic arylene, and monocyclic, bicyclic, and polycyclic heteroarylene, where each Ar1 and Ar2 may contain one to five of the arylene or heteroarylene each of which may be fused or linked.The fullerene is selected from but not limited to group of formula (i) and (ia).n=1-6;Ar'=independently selected from monocyclic, bicyclic, and polycyclic arylene, and monocyclic, bicyclic, and polycyclic heteroarylene, where each Ar' may contain one to five of the arylene or heteroarylene each of which may be fused or linked;Rx=independently selected from Ar', straight-chain, branched, and cyclic alkyl with 2-40 C atoms, where non-adjacent C atoms are optionally replaced by -O-, -S-, -C (O) -, -C (O-) -O-, -O-C (O) -, -O-C (O) -O-, -CR0=CR00-, or -CC-, and where H atoms are optionally replaced by F, Cl, Br, I, or CN or denote aryl, heteroaryl, aryloxy, heteroaryloxy, arylcarbonyl, heteroarylcarbonyl, arylcarbonyloxy, heteroarylcarbonyloxy, aryloxycarbonyl, or heteroaryloxycarbonyl having 4-30 ring atoms unsubstituted or substituted by non-aromatic groups;R0 and R00=independently a straight-chain, branched, or cyclic alkyl group;R1=independently selected from straight-chain, branched, and cyclic alkyl with 2-40 C atoms, where non-adjacent C atoms are optionally replaced by -O-, -S-, -C (O) -, -C (O-) -O-, -O-C (O) -, -O-C (O) -O-, -CR0=CR00-, or -CC-, and where H atoms are optionally replaced by F, Cl, Br, I, or CN or denote aryl, heteroaryl, aryloxy, heteroaryloxy, arylcarbonyl, heteroarylcarbonyl, arylcarbonyloxy, heteroarylcarbonyloxy, aryloxycarbonyl, or heteroaryloxycarbonyl having 4-30 ring atoms unsubstituted or substituted by non-aromatic groups, where the number of carbon that R1 contains is larger than 1;R0 and R00=independently a straight-chain, branched, or cyclic alkyl group;Ar1=independently selected from monocyclic, bicyclic and polycyclic heteroaryl groups, where each Ar1 may contain one to five of the heteroaryl groups each of which may be fused or linked; andAr2=independently selected from aryl groups containing more than 6 atoms excluding H; where the fullerene ball represents a fullerene selected from C60, C70, C84, and other fullerenes.The conjugated polymer comprises repeating units selected from group of formula (ii), for example (iia).X2=independently selected from S, Se, O, and N-R2;R2=selected from 1-30C straight-chain or branched alkyl groups;X3=independently selected from F, Cl, H, and Br; andAr2=independently selected from monocyclic, bicyclic, and polycyclic arylene, and monocyclic, bicyclic, and polycyclic heteroarylene, where each Ar2 may contain one to five of the arylene or heteroarylene each of which may be fused or linked.Preferably, the conjugated polymer comprises repeating units selected from group (iii), for example (iiia).X1=independently selected from S and Se;X3=independently selected from Cl and F;R=independently selected from 8-23C branched alkyl groups; andAr2=independently selected from substituted and unsubstituted bithiophene.The conjugated polymer comprises repeating units of formula 2 or 3.X2=independently selected from S and O;X3=independently selected from Cl and F;R=independently selected from 17-23C branched alkyl groups; andAr2=independently selected from substituted and unsubstituted bithiophene.Preferred Parameters: The conjugated polymer has an optical band gap of less than or equal to 1.8 eV, or more preferably, less than or equal to 1.65 eV. EXAMPLE - No suitable example given.