TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: Organic active layer contains n-type-semiconductor compound e.g. fullerene compound, borane derivative, thiazole derivative, benzothiazole derivative, benzothiadiazole derivative, perylene diimido derivative, naphthalene tetracarboxylic acid diimide, and/or n-type polymer substituted by alkyl. Photoelectric conversion element comprises buffer layer containing phosphine compound which has double bond between group 16 element and phosphorus atom. Photoelectric conversion element is solar cell.    TECHNOLOGY FOCUS - POLYMERS - Preparation (Disclosed): Copolymer is obtained by synthesizing benzodithiophene monomer, thieno thiophene monomer, and imide thiophene monomer, reacting, stirring, reprecipitating, purifying by gel permeation chromatography, and reprecipitating. SPECIFIC COMPOUNDS - 1 Compound is specifically disclosed, e.g. compound of formula (P1).    EXAMPLE - Benzodithiophene monomer of formula (M3), thieno thiophene monomer of formula (M1), and imide thiophene monomer of formula (M2) were synthesized. Benzodithiophene monomer (M3) (194 mg), thieno thiophene monomer (M1) (94 mg), and imide thiophene monomer (M2) (21 mg) were placed in a 100 ml flask. Anhydrous toluene (4.5 ml), anhydrous N,N-dimethylformamide (0.5 ml), and (tetrakistriphenylphosphine)palladium (8.6 mg) were added to reaction liquid. Reaction liquid was stirred at 130 degrees C for 8 hours, bromobenzene (200 mu l) was added, reaction liquid was stirred, phenyltin (200 mu l) was added continuously for 1.5 hours, and reaction liquid was stirred for 1 hour. Deaerated methanol was added after completion of reaction, and crude product was reprecipitated. Obtained crude product was dissolved in chloroform, purification by gel permeation chromatography was performed, and reprecipitation was carried out. Copolymer (P1) (60 mg, weight average molecular weight (Mw=2.0x 105), number average molecular weight (Mn=7.5x 104), polydispersity index (PDI) (Mw/Mn=2.7)) was obtained.