NOVELTY - The method involves providing liquid (1) at an aperture (13) of a hollow body (10) i.e. hollow lamp, such that the aperture is closed by the liquid. The liquid is moved into the hollow body through the aperture, where an inner surface (14) of the hollow body is enclosed by the liquid. The liquid is applied with working pressure and the volume of the inner space of the hollow body is changed such that the liquid is raised up to a predestinated liquid level (15) above the aperture. The inner surface of the hollow body is connected with environment of the hollow body over a gas line (31).    USE - Method for treating an inner surface of a hollow body of an optoelectronic component e.g. organic LED (OLED) illuminating device or photovoltaic device, (all claimed), with liquid for coating or cleaning of the inner surface of the hollow body. Uses include but are not limited to paint, suspension of an unsolvable substance, slurry, monomer solution of an organic substance, polymer solution of an organic substance, a liquid surface-active substance and a liquid with nanoparticles.    ADVANTAGE - The method enables applying the liquid with the working pressure and changing the volume of the inner space of the hollow body such that the liquid is raised up to the predestinated liquid level above the aperture, so that uniform supply of material takes place on the inner surface up to the desired liquid level. The method enables selecting the fluid level depending on the setting of the working pressure, thus simplifying treatment of sub-sections of the inner surface of the hollow body. The working pressure can be set with high accuracy, so that the desired corresponding portions can be treated with high accuracy.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for an optoelectronic component.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a hollow body in which the liquid is moved under action of pressure in inner surface of a hollow body.    Liquid (1)    Hollow body (10)    Aperture (13)    Inner surface (14)    Predestinated liquid level (15)    Gas line (31)