NOVELTY - A polymer consists of a repeating unit containing a 5-membered ring containing thiazolo-thiazole skeleton (I), and a heteroatom. The polymer has a hole mobility of 7.5x 10-5 cm2/Vs or more as measured by space charge limited current (SCLC) method, a solubility of 10 mg or more with respect to chlorobenzene (1 mL).    USE - Polymer is used as p-type organic semiconductor in organic photoelectric conversion elements (claimed) e.g. organic thin-film solar cells.    ADVANTAGE - The polymer has high charge mobility and high solubility, and provides organic photoelectric conversion elements having excellent photoelectric conversion efficiency and durability.    DETAILED DESCRIPTION - A polymer consists of a repeating unit containing a 5-membered ring containing thiazolo-thiazole skeleton of formula (I), and a heteroatom. The polymer has a hole mobility of 7.5x 10-5 cm2/Vs as measured by space charge limited current (SCLC) method, a solubility of 10 mg or more with respect to chlorobenzene (1 mL).    R1-R4=branched alkyl, linear alkyl, alkylester, carboxyalkyl, or alkoxy;and    X=S, O or N.    The ratio of linear alkyl in R1-R4 is 50% or less. An INDEPENDENT CLAIM is included for photoelectric conversion element (10) consisting of a p-type organic semiconductor, a photoelectric conversion layer (50) comprising the polymer as p-type organic semiconductor (52) and an n-type organic semiconductor (54) which form a bulk heterojunction, electrode (30) electrically connected with the photoelectric conversion layer and the light-receiving surface side of the photoelectric conversion layer, and electrode (70) electrically connected with the photoelectric conversion layer in the other side.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view of the photoelectric conversion element.    Photoelectric conversion element (10)    Electrodes (30,70)    Photoelectric conversion layer (50)    P-type organic semiconductor (52)    N-type organic semiconductor (54)