NOVELTY - A polymer (D1) comprising at least one divalent unit based on 4,8-bis(1,1-difluoralkyl)-benzo(1,2-b:4,5-b')dithiophene compound (I), is new.    USE - In polymer blend for used as charge transport, semiconducting, electrically conducting, photo conducting or light emitting material in an optical, electrooptical, electronic, electroluminescent or photoluminescent device or in a component of such a device, or in an assembly comprising such a device or component, where the component is selected from charge injection layers, charge transport layers, interlayers, planarizing layers, antistatic films, polymer electrolyte membranes, conducting substrates and conducting patterns, where the optical, electro-optical, electronic, electroluminescent or photoluminescent devices are selected from organic field effect transistors (OFET), organic thin film transistors, organic light emitting diodes, organic light emitting transistors, organic photovoltaic devices (OPV), organic solar cells, laser diodes, organic plasmon-emitting diodes, Schottky diodes, organic photoconductors and organic photodetectors, and where the assembly is selected from integrated circuits, radio frequency identification tags or security markings or security devices, flat panel displays or backlights of it, electrophotographic devices, electrophotographic recording devices, organic memory devices, sensor devices, biosensors and biochips; and also used as electrode materials in batteries, or in components or devices for detecting and discriminating DNA sequences, where the device is OFET, bulk heterojunction (BHJ) OPV device or inverted BHJ OPV device (claimed).    ADVANTAGE - The polymers are easy to synthesize, and provide large scale production using solution processing methods; show good processability, high stability, good solubility in organic solvents, high charge carrier mobility, and a low bandgap; are capable of enabling a reduction of the bandgap, and thereby improving light harvesting properties in bulk heterojunction (BHJ) photovoltaic devices; and are promising materials for organic electronic devices, especially for OPV devices with high power conversion efficiency.    DETAILED DESCRIPTION - A polymer (D1) comprising at least one divalent unit based on 4,8-bis(1,1-difluoralkyl)-benzo(1,2-b:4,5-b')dithiophene compound of formula (I), is new.    Y3=N or CR3;    Y4=N or CR4;    R1 and R2=straight-chain, branched or cyclic 1-30C (preferably 1-20C) alkyl (in which at least one non-adjacent C atom is optionally replaced by -O-, -S-, -C(O)-, -C(O)-O-, -O-C(O)-, -CH=CH- or -C?=C-) (optionally substituted with F, Cl, Br, I or CN);    R3 and R4=carbyl or hydrocarbyl group (both optionally substituted, and where at least one C atom is optionally replaced by hetero atom), H or halo.    INDEPENDENT CLAIMS are included for the followings:    (1) a mixture or polymer blend comprising the polymer (I) and at least one compound or polymer having semiconducting, charge transport, hole/electron transport, hole/electron blocking, electrically conducting, photo-conducting or light emitting properties;    (2) a formulation comprising the polymer (D1), the mixture or polymer blend, and at least one solvents (preferably organic solvents);    (3) new monomer of formula R7-(Ar1)a-U'-(Ar2)c-R8 (VI); and    (4) preparing the polymer (D1).    R7 and R8=Cl, Br, I, O-tosylate, O-triflate, O-mesylate, O-nonaflate, -SiMe2F, -SiMeF2, -O-SO2(Z'1), -B(OZ'2)2, -CZ'3=C(Z'3)2, -C?=CH, -C?=C-Si(Z'1)3, -ZnX'b or -Sn(Z'4)3;    X'b=Cl, Br or I;    Z'1-Z'4=alkyl or aryl (both optionally substituted);or    Z'2+Z'2=cyclic group.