NOVELTY - Oligo-para-phenylene-containing copolymers are new.    USE - In an electronic or electro-optic device (claimed) such as variety of photovoltaic applications e.g. polymer solar cells, filed effect transistors, electroluminescent device such as organic light emitting diode, electrostatic dissipation coating or packaging materials, chemical sensor, thin film semiconductor devices, photodetectors and photoconductors, or electrochemical devices such as rechargeable batteries, capacitors, supercapacitors, or electrochromic devices; or as component of block copolymer.    ADVANTAGE - The ladder-type oligo-para-phenylene-containing copolymers exhibit high open-circuit voltages and ambient photovoltaic activity and are useful in a variety of photovoltaic applications. The ladder-type oligo-para-phenylenes have electron donor building blocks and electron-accepting fused ring structures; such as 4,7-dithien-2-yl-2,1,3-benzothiadiazole or 5,8-dithien-2-yl-2,3-diphenylquinoxaline as electron acceptor building block to obtain copolymers having deeper highest occupied molecular orbital (HOMO) energy levels, and electron donor units to provide deeper HOMO to obtain polymeric solar cells having a higher open circuit voltage, broader spectral absorption ranges, and improved phase separation properties with (6,6)-phenyl 61C butyric acid methyl (PCBMs). The extended pi -conjugation of ladder-type oligo-para-phenylene derivatives can lead to broader, more intense absorption band compared to fluorene derivatives and, thus, result in better light harvesting such as enhanced solar light harvesting. The copolymers exhibit field effect mobilities as high as 0.011 cm2/(Vs). Compared to fluorene containing polymers with the same acceptor unit, the ladder-type oligo-para-phenylene-containing copolymers have enhanced and bathochromically shifted absorption bands and much better solubility in organic solvents. For electronic devices comprising organic materials, a solution process is highly desirable. Because the copolymers are soluble in common organic solvents, conventional methods known in the art can be used to cast polymeric materials comprising the copolymers to provide solid forms of the compositions, including thin films forms and printed forms. Thus, compositions comprising the copolymers (I) can be dissolved or dispersed in suitable solvent(s) and then coated onto a substrate and allowed to dry.    DETAILED DESCRIPTION - Oligo-para-phenylene-containing copolymer of formula (I) is new.    n=1-1000;    X=S, O, or NR6;    R6=H, or 1-4C linear or branched optionally substituted alkyl;    A'=electron-accepting fused ring system;    B'=linearly overlapping fluorene system comprising 2-9 fluorene groups (preferably a divalent radical selected from groups of formulae (i) to (viii));    R1=4-30C linear or branched optionally substituted alkyl chain (having at least one O, S, or N atom optionally substituted for a carbon atom).    An INDEPENDENT CLAIM is included for an electronic or electro-optic device comprising: a first electrode; a second electrode; and a layer of electroactive material operationally disposed between the first and the second electrode, where the electroactive layer comprises the compound (I).