NOVELTY - A polymer (P1) comprises a first comonomer repeat unit of a silacyclopentadithiophene moiety of formula (I); and a second comonomer repeat unit including a heterocyclic moiety e.g. the moiety (I), a benzothiadiazole moiety, thiadiazoloquinoxaline moiety, cyclopentadithiophene moiety, cyclopentadithiophene oxide moiety, benzoisothiazole moiety or benzothiazole moiety, is new.    USE - In article e.g. photovoltaic cell (claimed), organic field effect transistors and organic light-emitting diode devices.    ADVANTAGE - The polymer provides a photovoltaic cell with increase the current and efficiency; improves solubility in organic solvents and can form an photoactive layer with improved morphology; can absorb light at a relatively long wavelength; produces an electron donor material with improved semiconductive properties; is soluble in an organic solvent and/or film forming; and is optically non-scattering. The photovoltaic cell including the polymer creates high cell voltage; has relatively fast and efficient transfer of an electron to an electron acceptor material; has relatively fast charge separation, where the charge mobility of the positive charge, or hole, is relatively high and falls within the range of 10-4-10-1 cm2/Vs.    DETAILED DESCRIPTION - A polymer (P1) comprises a first comonomer repeat unit of a silacyclopentadithiophene moiety of formula (I); and a second comonomer repeat unit including the moiety (I), a benzothiadiazole moiety, thiadiazoloquinoxaline moiety, cyclopentadithiophene moiety, cyclopentadithiophene oxide moiety, benzoisothiazole moiety, benzothiazole moiety, thiophene oxide moiety, thienothiophene moiety, thienothiophene oxide moiety, dithienothiophene moiety, dithienothiophene oxide moiety, tetrahydroisoindole moiety, fluorene moiety, fluorenone moiety, thiazole moiety, selenophene moiety, silole moiety, thiazolothiazole moiety, cyclopentadithiazole moiety, naphthothiadiazole moiety, thienopyrazine moiety, oxazole moiety, imidazole moiety, pyrimidine moiety, benzoxazole moiety or benzimidazole moiety, is new.    R1-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.    An INDEPENDENT CLAIM is included for an article (such as photovoltaic cell) (100) comprising a first electrode; second electrode; and photoactive material disposed between the first and second electrodes, where the photoactive material comprising the polymer (P1) including a first comonomer repeat unit and a second comonomer repeat unit different from the first comonomer repeat unit.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a photovoltaic cell.    Photovoltaic cell (100)    Substrate (110)    Cathode (120)    Hole carrier layer (130)    Anode. (160)