TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The repeating unit (A) comprises a 2-thieno(3,4-b)thiophen-4-yl-1,6-dithia-dicyclopenta(b,g) naphthalene repeating unit of formula (XI) or a 2-thieno(3,4-b)thiophen-4-yl-1,7-dithia-dicyclopenta(b,i)anthracene repeating unit of formula (XIII). The repeating unit (B) comprises or 2-thieno(3,4-b)thiophen-4-yl-benzo(1,2-b;4,5-b')dithiophene repeating unit of formula (XII). The electron-donating polymer and the repeating unit A have a band gap of 1.1-2.5 eV. The electron-donating polymer and the repeating unit B have hole mobility of 1x 10-6 cm2/V.s to 9x 101 cm2/V.s. The mole ratio of the repeating unit A and the repeating unit B is 1:10-10:1. The electron-donating polymer has a number average molecular weight of 1000-800000.X1a-X4a, X5b-X10b = 1-20C-alkyl, 1-20C-alkoxy, 1-20C-ester (all optionally substituted) or H, provided that at least one of X1a-X4a and X5b-X10b is one of 1-20C-alkyl, 1-20C-alkoxy or 1-20C-ester (all optionally substituted);X11a, X11b = H or halo;X12a, X12b = 1-20C-alkyl, 1-20C-alkoxy or 1-20C-ester (all optionally substituted);R1a, R2a, R3b, R4b = H or optionally substituted 1-20C-alkyl;X13a, X14a = 1-20C-alkyl, 1-20C-alkoxy, 1-20C-ester (all optionally substituted) or SR104a;R104a = optionally substituted 1-20C-alkyl;X15a = H or halo;X16a = 1-20C-alkyl, 1-20C-alkoxy or 1-20C-ester (all optionally substituted); andR5a, R6a = H or optionally substituted 1-20C-alkyl. EXAMPLE - Bis(trimethyltin)-5,11-bis(octyloxy)anthra(2,3-b:6,7-b')dithiophene (0.06 mmole), 2,6-bis(trimethyltin)-1,8-bis((2-ethylhexyl)oxy)benzo(l,2-b:4,5-b')dithiophene (0.18 mmole), and dodecyl carboxy-6-dibromothieno(3,4-b)thiophene (0.24 mmole) were introduced in a mixture (7.5 ml) of dimethylformamide/toluene prepared in a volume ratio of 1:4. Further tetrakis(triphenylphosphine)palladium(0) (0.011 mmole) was added and the resulting mixture was stirred at 120 degrees C for 6 hours to obtain corresponding electron-donating polymer with a number average molecular weight of 12000.