NOVELTY - A thiophene compound is new.    USE - The thiophene compound or polymer is useful for preparing blend for use in photovoltaic device or opto-electronic device; and for stabilizing morphology of bulk-heterojunction photovoltaic cell (all claimed).    ADVANTAGE - The invention provides new thiophene-based polymers for enabling the manufacture of morphologically stable bulk heterojunction photovoltaic cells without making use of a cross-linking step and without making use of photo-initiators.    DETAILED DESCRIPTION - A thiophene compound of formula (I), is new.    L=a linear or branched alkylene group having from 1 to 10 carbon atoms;    J=a hydrogen atom or a linear or branched alkyl group having from 1 to 4 carbon atoms; and    X and Y=independently selected from hydrogen, chloro, bromo, iodo, boronic acid, boronic esters and organotin.    INDEPENDENT CLAIMS are:    (1) a polymer comprising monomer units of formula (IV);    (2) a method for producing the polymer comprising polymerizing by reductive coupling thiophene compound of formula (I) and optionally a comonomer of formula X'-Ar-Y';    (3) a blend for use in a photovoltaic device, comprising: (a) a polymer having a monomer unit of formula (IX); and (b) an electron acceptor such as a fullerene derivative; and    (4) an opto-electronic device comprising the blend.    L=linear or branched alkylene group having from 1 to 10 carbon atoms;    J=a hydrogen atom or a linear or branched alkyl group having from 1 to 4 carbon atoms;    Ar=homocyclic or heterocyclic aromatic group;    X' and Y'=independently selected from hydrogen, chloro, bromo, iodo, boronic acid, boronic esters and organotin with the proviso that X and Y are not simultaneously hydrogen;    L'=L-C(O)O-J, L-C(O)NR'-J, L-OCO-J', L-NR'CO-J', L-SCO-J', L-O-J, L-S-J, L-Se-J, L- NR'-J and L-CN;    J'=group having from 1 to 10 carbon atoms, being saturated or unsaturated, linear or branched, comprising a phenyl unit or not comprising a phenyl unit; and    R'=a hydrogen atom or a linear or branched alkyl group having from 1 to 4 carbon atoms.