TECHNOLOGY FOCUS - ELECTRONICS - Preferred Components: The light emitting thin film or the conductive thin film or the organic semiconductor thin film further comprises one or more compounds comprising a hole transporting material, an electron transporting material or a light emitting material. The polymer light emitting device comprises an organic layer between electrodes consisting of an anode and a cathode where the organic layer comprises the polymer compound. The organic layer further comprises one or more compounds comprising a hole transporting material, an electron transporting material, and a light emitting material. The organic layer is a light emitting layer. The light emitting material is a phosphorescent compound having iridium, platinum or europium as a central metal. WIDER DISCLOSURE - Polymer compound (Aa) comprising fused thiophene- or fused furan-units (Aaa) and (Aab) and having a polystyrene reduced number average molecular weight of 103-108, is also disclosed as new.    ring A-D = aromatic ring; and    X = S or O.    Preparation of (Aa) comprises condensation polymerization of a compound of formula (Y1-U1-Y1).    U1 = repeating unit (Aaa) or (Aab); and    Y1, Y2 = substituent capable of condensation polymerization.    EXAMPLE - 3,7-Dibromo-2,8-bis-octyloxy-dibenzothiophene (352 mg) and 2,2'-bipyridyl (274 mg) was dissolved in tetrahydrofuran (dehydrated, 20 ml). The inside of the system was replaced with nitrogen by bubbling with nitrogen gas. To this solution, bis(1,5-cyclooctadiene)nickel (0) (500 mg) was added, and the temperature was raised to 60 degrees C and reacted for 3 hours. After the reaction, the reaction liquid was cooled to a room temperature and added dropwise to a mixed solution of 25% aqueous ammonia (10 ml)/methanol (120 ml)/ion exchanged water (50 ml) and stirred for 1 hour. The deposited precipitate was filtrated and dried for 2 hours under reduced pressure, and dissolved in toluene (30 ml). Then, 1N hydrochloric acid (30 ml) was added and stirred for 1 hour, the aqueous layer was removed, 30 ml of 4% aqueous ammonia was added to the organic layer, and the aqueous layer was removed after stirring for 1 hour. The organic layer was added dropwise to methanol (200 ml) and stirred for 1 hour, then the deposited precipitate was filtrated and dried under reduced pressure for 2 hours and dissolved in toluene (30 ml). The recovered toluene solution was added to methanol (250 ml), stirred for 1 hour and deposited precipitate was filtrated and dried under reduced pressure for 2 hours to obtain a polymer having a polystyrene reduced average molecular weight 2.1x 104. A chloroform solutions (0.2 wt.%) of the polymer obtained was spin-coated on quartz to form a thin film.