NOVELTY - The functional organic thin film is formed using specific silicon compound, on a substrate.    USE - For organic thin-film transistor (claimed) and solar cell.    ADVANTAGE - The organic thin film has excellent electrical, optical and electrochemical properties. The formation of the organic thin film is performed simply. Crystallinity of the thin film is increased.    DETAILED DESCRIPTION - The functional organic thin film is formed using a silicon compound of formula R-SiX1X2X3, on a substrate.    R = organic residue formed by multiple units of optionally substituted pi-electron conjugated system coupled with the terminal in a functional group;and    X1-X3 = same or different groups which give hydroxyl group by hydrolysis.    INDEPENDENT CLAIMS are included for the following:    (1) manufacture of functional organic thin film. The method involves forming a functional organic thin film on a substrate by chemical absorption process;    (2) organic thin-film transistor. The transistor has a gate electrode formed at one surface of the organic thin film via a gate insulation film, and a source or drain electrode formed at other surface of the organic thin film;    (3) manufacture of organic thin-film transistor. A gate electrode is formed at the surface of an organic thin film provided on substrate, via gate insulation film, and source or drain electrode is formed at one or more surfaces of the organic thin film. The gate and drain electrodes are contacted, to obtain the transistor;    (4) pi-electron conjugated system molecule-containing silicon compound, which has formula R-SiX1X2X3; and    (5) manufacture of pi-electron conjugated system molecule-containing silicon compound. The method involves reacting compound of formula R1-Li and compound of formula (Y-SiX1X2X3), to obtain compound of formula (R1-SiX1X2X3).    R,X1-X3 = same as defined above;    R1 = organic residue of pi-electron system originating from heterocyclic compound of monocyclic aromatic hydrocarbon or monocyclic ring formed by coupling 3-10 units, and having functional group at the terminal;and    Y = H, halogen atom or lower alkoxy group.    DESCRIPTION OF DRAWING(S) - The figure shows the conceptual diagram for demonstrating the film-formation method of an accumulation monomolecular film.