NOVELTY - A copolymer containing 2,7-carbazole-benzodiazepine (benzothiadiazole) contains 2,7-carbazole-benzodiazepine (benzothiadiazole) derivative.    USE - A copolymer containing 2,7-carbazole-benzodiazepine (benzothiadiazole) for organic solar battery and organic electroluminescent device (all claimed). Can also be used for organic field effect transistor.    ADVANTAGE - Copolymer has strong donor-acceptor structure, improves stability of material, and reduces material energy band gap to expand sunlight absorption range and improve photoelectric conversion efficiency, and preparation method is easy to control and has high yield and mild reaction conditions.    DETAILED DESCRIPTION - A copolymer containing 2,7-carbazole-benzodiazepine (benzothiadiazole) contains 2,7-carbazole-benzodiazepine (benzothiadiazole) derivative of formula (I).    R1, R2, R3=1-20C alkyl; and    n=1-100.    An INDEPENDENT CLAIM is included for preparation of copolymer containing 2,7-carbazole-benzodiazepine (benzothiadiazole) which involves carrying out ring-closing reaction to brominated benzothiadiazole derivative of formula (A) and dialkyl acetylene of formula (B) with molar ratio of 1:2 under inert atmosphere dissolved in 1st solvent in the presence of catalyst and alkali solution at 100-150 degrees C for 2-6 hours to obtain brominated benzodiazepine (benzothiadiazole) derivative of formula (C), dissolving carbazole derivative of formula (D) in tetrahydrofuran solvent under inert atmosphere, placing in - 78 degrees C condition, adding n-butyllithium, stirring to react for 1-2 hours, adding 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane of formula (II), continuously reacting for 1 hour, warming to room temperature for 6 hours to obtain carbazole-dioxaborolane derivative of formula (E) in which molar ratio compound (D):n-butyllithium is 1:2, and molar ratio compound (II):compound (D) is 2:1, mixing compound (C) and compound (E) with molar ratio of 1:1.5-1.5:1 under inert atmosphere, adding 2nd solvent in the presence of 2nd catalyst and alkali, and performing Suzuki coupling reaction at 50-120 degrees C for 6-108 hours.