NOVELTY - A copolymer containing naphthodithiophene units and diketopyrrolopyrrole units (I), is new.    USE - Copolymer for use in construction of photovoltaic devices such as photovoltaic cells and photovoltaic modules on both rigid and flexible supports, construction of organic thin film transistors or organic field effect transistors.    ADVANTAGE - The copolymer has electronic and optical characteristics (good HOMO and LUMO orbital values, a good adsorption coefficient), good solubility in the solvents, reasonable mobility of the electronic gaps, good compatibility, high photo-stability, low band-gap value, certain crystallinity degree, and provides the device with high conversion efficiency.    DETAILED DESCRIPTION - A copolymer containing naphthodithiophene units and diketopyrrolopyrrole units of formula (I), is new.    R1, R1' = cycloalkyl, aryl (both optionally substituted), linear or branched 1-20C alkyl, linear or branched 1-20C alkoxyl, polyethyleneoxyl moiety of formula (-O-(CH2-CH2-O)p-R3), -R4-OH, -R5-CN, -COR6, -COOR7, -CHO or cyano;    R2, R2' = cycloalkyl, aryl (both optionally substituted), linear or branched 1-20C alkyl, linear or branched 1-20C alkoxyl, polyethyleneoxyl moiety of formula (-R8-O-(CH2-CH2-O)p-R9), -R10-OH, -R11-OR12 or -R13-CN;    R3, R8, R9 = hydrogen or linear or branched 1-20C alkyl;    p = 1-4;    R4-R7, R10-R13 = linear or branched 1-20C alkyl;    Y1 = heteroarylene, penta- or hexa-atomic, benzocondensed or heterobicyclic, containing 1-4 heteroatoms selected from nitrogen, oxygen, sulfur, silicon, selenium, phosphorus, such as thiophenylene, thienothiophenylene, pyridinolene, 3,4-dialkyithiophenylene, 3,4-dialkoxythiophenylene, 2,7-(9,9-dialkyl)-fluorenylene, 3,6-(9-alkyl)carbazolene, 2,7-(9-alkyl)carbazolene, 4,7-(2-alkyl)benzo-2,1,3-triazolene, 10-alkyl-acridolene or arylene , where the alkyl is a linear or branched 1-20C alkyl and the alkoxy is a linear or branched 1-20C alkoxyl, the arylene is optionally substituted with -CR14, -COR14, linear or branched 1-20C alkyl or aryl;    R14 = H or linear or branched 1-20C alkyl;    m = 1 or 2; and    n = 1-500, preferably 20-300.    An INDEPENDENT CLAIM is also included for the preparation of the copolymer containing naphthodithiophene units and diketopyrrolopyrrole units (I).