TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The first polymer: comprises a first co-monomer repeat unit comprising silacyclopentadithiophene moiety of formula (A1) or cyclopentadithiophene moiety of formula (A2); further comprises a third co-monomer repeat unit different from the first and second co-monomer repeat units, and the third co-monomer repeat unit comprises (A1) or (A2); and comprises 7,7-bis-(2-ethyl-hexyl)-2-(benzo(1,2,5)thiadiazol-4-yl)silacyclopentadithiophene of formula (A4), 7,7-bis-(2-ethyl-hexyl)-2-(benzo(1,2,5)thiadiazol-4-yl)cyclopentadithiophene of formula (A5), 7,7-bis-(2-ethyl-hexyl)-2-(7-(7,7-bis-(2-ethyl-hexyl)-2-benzo(1,2,5)thiadiazol-4-yl-cyclopentadithiophene-5-yl)-benzo(1,2,5)thiadiazol-4-yl)silacyclopentadithiophene of formula (A6). The second co-monomer repeat unit in the first polymer comprises a benzothiadiazole moiety of formula (A3). The monomer repeat unit in the second polymer comprises thiophene moiety of formula (A7). The electron acceptor material comprises fullerenes, inorganic nanoparticles, oxadiazoles, discotic liquid crystals, carbon nanorods, inorganic nanorods, polymers containing cyano groups, polymers containing trifluoromethyl groups, preferably substituted fullerene including (6,6)-phenyl C61-butyric acid methyl ester (C60-PCBM), (6,6)-phenyl C71-butyric acid methyl ester (C70-PCBM), bis(1-(3-(methoxycarbonyl)propyl)-1-phenyl)(6.6)C62 (bis-C60-PCBM) or 3'-phenyl-3'H-Cyclops(8,25)(5,6)fullereneC70-bis-D5h(6)-3'-butanoic acid methyl ester (bis-C70-PCBM). The weight ratio of the first and second polymers is 20:1-1:20, preferably 1:4. The first polymer, second polymer, and the electron acceptor material has a first highest occupied molecular orbital (HOMO) level, second HOMO level and third HOMO level, respectively, or has a first lowest unoccupied molecular orbital (LUMO) level, second LUMO level and third LUMO level, respectively, where the first HOMO level is between the second and third HOMO levels, or the first LUMO level is between the second and third LUMO levels. The weight ratio of the electron donor material and the electron acceptor material is 1:1-1:3, preferably 1:1. The photoactive layer has a thickness of at least 150 nm.R1, R2 = H, 1-20C alkyl, 1-20C alkoxy, 3-20C cycloalkyl, 1-20C heterocycloalkyl, (hetero)aryl, halo, CN, OR, C(=O)R, C(=O)OR, or SO2R, preferably H, 2-ethylhexyl or hexyl;R3, R4 = H, 1-20C alkyl, 1-20C alkoxy, 3-20C cycloalkyl, 1-20C heterocycloalkyl, (hetero)aryl, halo, CN, OR, C(=O)R, C(=O)OR, or SO2R;R = H, 1-20C alkyl, 1-20C alkoxy, (hetero)aryl, 3-20C cycloalkyl or 1-20C heterocycloalkyl;m, n = 1-1000; andR5-R8 = H, 1-20C alkyl, 1-20C alkoxy, 3-20C cycloalkyl or 1-20C heterocycloalkyl.