NOVELTY - Polymer (P1) comprising at least one substituted tricyclic units (I) and at least one N-containing tricyclic units (II), is new.    USE - The polymer (P1), mixture or polymer blend or formulation is useful as charge transport, semiconducting, electrically conducting, photoconducting 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 device is organic field effect transistors (OFET), thin film transistors, organic LED, organic light emitting transistors, organic photovoltaic devices (OPV), organic photodetectors, organic solar cells, laser diodes, Schottky diodes or photoconductors, the component is charge injection layers, charge transport layers, interlayers, planarizing layers, antistatic films, polymer electrolyte membranes, conducting substrates or conducting patterns, the assembly is integrated circuits, radio frequency identification tags or security markings or security devices containing them, flat panel displays or its backlight, electrophotographic devices, electrophotographic recording devices, organic memory devices, sensor devices, biosensors or biochips, and the device is an OFET, bulk heterojunction (BHJ) OPV device or inverted BHJ OPV device (all claimed).    ADVANTAGE - The polymer: is easy to synthesize; exhibits good processibility, high stability, good solubility in organic solvents, high charge carrier mobility, and a low band-gap; exhibits high external quantum efficiencies in BHJ solar cells, good morphology when used in p/n-type blends e.g. with fullerenes, high oxidative stability, and a long lifetime in electronic devices; and provides the organic photodetector devices with high power conversion efficiency.    DETAILED DESCRIPTION - Polymer (P1) comprising at least one substituted tricyclic units of formula (I) and at least one N-containing tricyclic units of formula (II), is new.    X1a = SiR1aR2a, CR1aR2a, NR1a or GeR1aR2a, preferably Si; and    R1a-R8a = carbyl, 1-40C hydrocarbyl (both optionally substituted) or H, where at least one of R1a and R3a is different from H and at least one of R3a to R8a is different from H.    INDEPENDENT CLAIMS are also included for:    (1) a mixture or polymer blend comprising at least one polymer (P1) and at least one compound or polymer (P2) having semiconducting, charge transport, hole/electron transport, hole/electron blocking, electrically conducting, photoconducting or light emitting properties;    (2) a formulation comprising at least one polymer (P1), mixtures or polymer blends, and at least one solvent, preferably organic solvents; and    (3) a monomer of formula (R1r-(Ar1a)b1-(D1a)d1-(Ar2a)c1-(A1a)a1-(Ar2a)b1-R2r).    D1a = unit (I);    A1a = unit (II);    Ar1a, Ar2a = arylene or heteroarylene with 5-30 ring atoms that is optionally substituted, preferably by at least one R1s;    b1, c1, d1 = 0-3;    R1r, R2r = Cl, Br, I, O-tosylate, O-triflate, O-mesylate, O-nonaflate, -Si(CH3)2F, -Si(CH3)F2, -O-SO2Z1a, -B(OZ2a)2, -CZ3a=C(Z4a)2, -CCH, -CC-Si(Z1a)3, -ZnX1r or -Sn(Z4a)3, preferably Cl, Br, I, -B(OZ2a)2 or -Sn(Z4a)3, with each other in aryl-aryl coupling reaction;    X1r = halo, preferably Cl, Br or I; either    Z1a-Z4a = alkyl or aryl (preferably 1-12C alkyl or 4-10C aryl) (both optionally substituted); or    two of Z2a = cyclyl with B and O-atoms; and    a1 = 1-3.