TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The second comonomer repeat unit comprises a silacyclopentadithiophene moiety, a benzothiadiazole moiety, a thiadiazoloquinoxaline moiety, a cyclopentadithiophene moiety, a cyclopentadithiophene oxide moiety, a benzoisothiazole moiety, a benzothiazole moiety, a thiophene oxide moiety, a thienothiophene moiety, a thienothiophene oxide moiety, a dithienothiophene moiety, a dithienothiophene oxide moiety, a tetrahydroisoindole moiety, a fluorene moiety, a fluorenone moiety, a thiazole moiety, a selenophene moiety, a silole moiety, a thiazolothiazole moiety, a cyclopentadithiazole moiety, a naphthothiadiazole moiety, a thienopyrazine moiety, a thiophene moiety, an oxazole moiety, an imidazole moiety, a pyrimidine moiety, a benzoxazole moiety, or a benzimidazole moiety. The first comonomer repeat unit comprises a cyclopentadithiazole moiety of formula (I). The second comonomer repeat unit comprises a cyclopentadithiazole moiety (I), a benzothiadiazole moiety of formula (II), a thiadiazoloquinoxaline moiety of formula (III), a cyclopentadithiophene dioxide moiety of formula (IV), a cyclopentadithiophene monoxide moiety of formula (V), a benzoisothiazole moiety of formula (VI), a benzothiazole moiety of formula (VII), a thiophene dioxide moiety of formula (VIII), a cyclopentadithiophene dioxide moiety of formula (IX), a cyclopentadithiophene tetraoxide moiety of formula (X), a thienothiophene moiety of formula (XI), a thienothiophene tetraoxide moiety of formula (XII), a dithienothiophene moiety of formula (XIII), a dithienothiophene dioxide moiety of formula (XIV), a dithienothiophene tetraoxide moiety of formula (XV), a tetrahydroisoindole moiety of formula (XVI), a thienothiophene dioxide moiety of formula (XVII), a dithienothiophene dioxide moiety of formula (XVIII), a fluorene moiety of formula (XIX), a silole moiety of formula (XX), a cyclopentadithiophene moiety of formula (XXI), a fluorenone moiety of formula (XXII), a thiazole moiety of formula (XXIII), a selenophene moiety of formula (XXIV), a thiazolothiazole moiety of formula (XXV), a naphthothiadiazole moiety of formula (XXVI), a thienopyrazine moiety of formula (XXVII), a silacyclopentadithiophene moiety of formula (XXVIII), a thiophene moiety of formula (XXIX), an oxazole moiety of formula (XXX), an imidazole moiety of formula (XXXI), a pyrimidine moiety of formula (XXXII), a benzoxazole moiety of formula (XXXIII), or a benzimidazole moiety of formula (XXXIV).R1, R2, R5, R6 = H, 1-20C alkyl, 1-20C alkoxy, 3-20C cycloalkyl, 1-20C heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR or SO2R;R, R7, R8 = H, 1-20C alkyl, 1-20C alkoxy, aryl, heteroaryl, 3-20C cycloalkyl or 1-20C heterocycloalkyl; andX,Y1 = CH2, O or S.