TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The n-type organic semiconductor compounds are fullerenes or substituted fullerenes.    TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): Monomers of formulae: R7-U'-R8 (i), R7-Sp-R8 (ii) and R7-(Sp)x-U'-(Sp)y-R8 (iii) coupled with each other and co-monomers are subjected to aryl-aryl coupling reaction to obtain polymer (II).U'=group of formula (I), donor unit, or acceptor unit;Sp=spacer unit;y=0, 1 or 2;R7,R8=group comprising activated C-H bond, Cl, Br, I, O-tosylate, O-triflate, O-mesylate, O-nonaflate, -SiMe2F, -SiMeF2, -O-SO2Z1, -B(OZ2)2 , -CZ3=C(Z3)2, -OCH, -CC-Si(Z1)3, -ZnX0, or -Sn(Z4)3;X0=halo, preferably Cl, Br or I;andZ1-Z4=optionally substituted alkyl or aryl.Preferred Composition: The unit (D) is chosen from 141 groups e.g. groups of formulae (D1)-(D50). The unit (A) is chosen from 97 groups e.g. groups of formulae (A1)-(A50). The spacer units are chosen from groups of formulae (Sp1)-(Sp-16). The polymer is chosen from 71 polymers e.g. polymers of formulae (II)-(VI). The mixture or polymer blend comprises 1 or more polymers and 1 or more n-type organic semiconductor compounds.R11-R19=H, or Rs;Rs=F, Br, Cl, -CN, -NC, -NCO, -NCS, -OCN, -SCN, -C(O)NR0R00, -C(O)X, -C(O)R0, -C(O)OR0, -NH2, -NR0R00, -SH, -SR0, -SO3H, -SO2R0, -OH, -NO2, -CF3, -SF5, optionally substituted silyl, carbyl or 1-40C hydrocarbyl;X1=X;a,b,c,d=0-1 (excluding 1);n=more than 1;andx=0,1 or 2. EXAMPLE - 2,6-Dibromo-benzo(1,2-b;4,5-b')dithiophene-4,8-dicarboxylic acid didodecyl ester, 2,5-bis-trimethylstannanyl-thiophene, 4,7-dibromo-5,6-bis-octyloxy-benzo(1,2,5)thiadiazole, 4,8-dibromo-6-(2-ethyl-hexyl)-(1,2,5)thiadiazolo(3,4-e)isoindole-5,7-dione, tris(dibenzylideneacetone)dipalladium(0) and tri-o-tolyl-phosphine were added to reactor, and nitrogen gas was purged into the reactor. The reaction mixture was heated, and polymerized, and cooled. Bromobenzene was added to the reaction mixture, cooled and tributyl-phenyl-stannane was added and heated. The reaction mixture was cooled, precipitated, filtered and washed with methanol to obtain polymer of formula (I-a) having number average molecular weight of 17.6 kg.mol-1, and weight average molecular weight of 47.5 kg.mo1-1.