TECHNOLOGY FOCUS - POLYMERS - Preparation (Disclosed): Preparation of the copolymer comprises carrying out carbon-carbon coupling reaction e.g. Stille coupling reaction and Suzuki coupling reaction of the monomers, to give the copolymer. Preferred Components: The unit different from the first unit includes: at least one electron acceptor, where the electron acceptor is present at greater than 0 mole% to less than or equal to 50 mole% based on the total moles of the monomers; or at least one electron acceptor and at least one electron donor; or at least two electron acceptors and at least one electron donor. The electron acceptor is substituted hydrocarbyl units of formulae (a1)-(a8), preferably substituted benzo(c)(1,2,5)thiadiazole-4,7-diyl of formula (III) (as second unit). The electron donor is substituted hydrocarbyl units of formulae (b1)-(b15), preferably substituted 9H-fluorene-2,7-diyl of formula (IV) (as third unit). The copolymer comprises substituted 9H-carbazole-3,6-diyl of formula (-((A1-B1-)l-(C1-D1-)m-)n-) (II) or (-((d1-d2)m-(d3-d4)l-)n-) (V). The copolymer further comprises substituted 4-(5-(9H-carbazol-3-yl)thiophen-2-yl)-7-(thiophen-2-yl)benzo(c)(1,2,5)thiadiazole of formula (VI) (as fourth unit) and substituted 2-(5-(7-thiophen-2-yl-benzo(1,2,5)thiadiazol-4-yl)-thiophen-2-yl)-9H-carbazole of formula (VII) (as fifth unit).X1-X3 = CR1R2, NR1, O, SiR1R2, PR1, S, GeR1R2, Se or Te;Y1-Y4 = CR1, N, SiR1, P or GeR1; eitherR2-R11, R1, and R2 = R1a; oradjacent two of R2 and R3, R2-R5, R6 and R7, R8-R11, and R1 and R2 = condensed ring;b = 0-6;c = 0-8;X1-X3 = CR1R2, NR1, O, SiR1R2, PR1, S, GeR1R2, Se or Te;Y1, Y2 = CR1, N, SiR1, P or GeR1;l = mole fraction of greater than 0 to less than or equal to 1;m = mole fraction of 0 to less than 1;n = 1-10000;B1, C1, D1 = electron acceptor or electron donor, where at least one of B1, C1 and D1 is electron acceptor;a, s, and t = 0-4;R1, R2, and R3 = R1a;d, e, q, r = 0-3;d1 = (IV);d2 = (III);A1, d3 = (I); andd4 = substituted benzo(c)(1,2,5)thiadiazole-4,7-diyl of formula (VIII).In the copolymer, (I) is present at greater than 0 to 10 mole% based on the total moles of monomers constituting the polymer, (III) is present at greater than 0 to 50 mole% based on the total moles of the monomers, and (IV) is present at more than 0 to 40 mole% based on the total moles of the monomers. The copolymer has: an aryl group as its end group; a heterocyclic group as its end group; a number average molecular weight of 500-1000000 g/mol; and a molecular weight distribution of 1-100. The organic material layers comprise at least one electron donor or electron acceptor, where the electron donor is the copolymer, and the electron acceptor is fullerene and its derivatives, carbon nanotubes and their derivatives, vasocuproin (sic), semiconductor elements, and/or semiconductor compounds, preferably the electron acceptor is a C60 fullerene derivative or a C70 fullerene derivative. The copolymer and the electron acceptor are mixed with each other at a weight ratio of 1:0.5-1:4. EXAMPLE - 9-(1-Octyl-nonyl)-3,6-bis-(4,4,5,5-tetramethyl-(1,3,2)dioxaborolan-2-yl)-9H-carbazole (4.1 mg), 9-(1-octyl-nonyl)-2,7-bis-(4,4,5,5-tetramethyl-(1,3,2)dioxaborolan-2-yl)-9H-carbazole (201 mg), 4,7-bis-(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (143 mg), 20% aqueous solution of tetraethylammonium hydroxide (3 ml), tetrakis(triphenylphosphine)palladium(0) (5 mg) and Aliquat 336 (RTM: Quaternary ammonium salt) were added to toluene (3 ml) and stirred under reflux. After 72 hours, phenylboronic acid (0.05 g) was added to and reacted with the reaction mixture for 3 hours, after which bromobenzene (0.12 g) was added to and reacted with the mixture for 4 hours. Then, the reaction mixture was cooled to room temperature and poured into methanol. The solid was filtered and Soxhlet-extracted with acetone, hexane and chloroform. The extract was precipitated in methanol, and filtered to obtain the copolymer (55%).