NOVELTY - A pi-electron conjugated-type block copolymer contains a polymer block (A) comprising a monomer unit having heteroaryl skeleton of dibenzogermole, dibenzogermole, carbazole, fluorine and hiophene, and a polymer block (B) comprising a monomer unit having at least one heteroaryl skeleton contiguously or non-contiguously bonded in a portion of the chemical structure of the pi-electron conjugated block copolymer. The polymer block (B) is copolymer block of monomer unit having alkoxy, halo, hydroxy, amino, thiol, silyl, ester, aryl or 1-18C alkyl as substituent groups.    USE - Pi-electron conjugated-type block copolymer is used for composition for photoelectric conversion element (all claimed). Uses include but are not limited to organic thin-film solar cell, optical sensor, optical switch, photo-transistor and optical memory.    ADVANTAGE - The photoelectric conversion element containing pi-electron conjugated-type block copolymer has excellent conversion efficiency, and can control morphology.    DETAILED DESCRIPTION - A pi-electron conjugated-type block copolymer contains a polymer block (A) comprising a monomer unit having heteroaryl skeleton of dibenzogermole, dibenzogermole, carbazole, fluorine and hiophene, and a polymer block (B) comprising a monomer unit having at least one heteroaryl skeleton contiguously or non-contiguously bonded in a portion of the chemical structure of the pi-electron conjugated block copolymer. The polymer block (A) is a homopolymer block of a monomer unit having alkoxy or 1-18C alkyl as substituent group. The polymer block (B) is copolymer block of monomer unit having heteroaryl, alkoxy (both optionally substituted), alkoxy, halo, hydroxy, amino, thiol, silyl, ester, aryl or 1-18C alkyl as substituent groups. INDEPENDENT CLAIMS are included for the following:    (1) composition, which contains pi-electron conjugated system block copolymer in electron-accepting material; and    (2) photoelectric conversion element, which has a layer containing composition.