TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Parameter: The titanium oxide layer has a thickness of 5-500, preferably 10-40 nm. Preferred Component: The titanium oxide layer is positioned adjacent to the photoactive, charge-separating layer, or between the photoactive, charge-separating layer and one of the two electrodes. It is a boundary layer of the photovoltaic cell. The first electrode comprises a transparent hole injecting layer and indium-tin-oxide (ITO) bilayer electrode. The passivating layer is positioned between the second electrode and the photoactive polymer layer. The titanium oxide precursor comprises titanium(IV) butoxide, titanium(IV) chloride, titanium(IV) ethoxide, titanium(IV) methoxide, titanium(IV) propoxide, and titanium disulfate (Ti(SO4)2). Preferred Method: The solution of titanium oxide precursor is applied by spin-coating onto the photoactive, charge-separating layer. The method comprises heating the applied solution at 50-150, preferably 80-120degreesC.    TECHNOLOGY FOCUS - METALLURGY - Preferred Component: The second electrode comprises a metal electrode.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The photoactive polymer layer comprises a heterojunction layer comprising poly(3-hexylthiophene) and (6,6,)-phenyl-C61-butyric acid methyl ester. EXAMPLE - Titanium(IV) isopropoxide (10 ml) was mixed with 2-methoxyethanol (50 ml) and ethanolamine (5 ml). The mixed solution was then heated to 80degreesC for 2 hours in a silicon oil bath under magnetic stirring, followed by heating to 120degreesC for 1 hour. The two-step heating (at 80 and 120degreesC) was then repeated. A TiOx precursor solution was prepared in isopropyl alcohol. Dense TiOx layers were prepared from TiOx precursor solution. The precursor solution was spin-cast in the air on top of a semiconducting polymer layer comprising poly(3-hexylthiophene) with thicknesses of 20-40 nm. Subsequently, the films were heated at 80degreesC for 10 minutes in the air. During the process, the precursor converted to a solid-sate TiOx layer. An atomic force microscope scan showed that the resulting TiOx film was smooth and transparent with surface features smaller than a few nm. X-ray diffraction results confirmed that TiOx film was amorphous.